Abstracts of Posters

Magnetic Resonance Imaging 21 (2003) 421– 450

Abstracts of Posters Influence of stagnant zones on transient and asymptotic dispersion in macroscopically homogeneous porous media D. Kandhai1,2, D. Hlushkou3,4, A. Hoekstra1, P. M. A. Sloot1, H. Van As3, U. Tallarek3,5 1Section of Computational Science, University of Amsterdam, Amsterdam, The Netherlands 2Kramers Lab. of Physical Technology, Delft University of Technology, Delft, The Netherlands 3 Laboratory of Biophysics and Wageningen NMR Centre, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands 4Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany 5Lehrstuhl fu¨r Chemische Verfahrenstechnik, Otto-von-Guericke Universita¨t Magdeburg, Universita¨tsplatz 2, 39106 Magdeburg, Germany. Figure 1. A detailed understanding of transport in porous media over the intrinsic temporal and spatial scales is important in many technological and environmental processes. Natural and industrial materials like soil, rock, filter cakes or catalyst pellets often contain low-permeability zones with respect to hydraulic flow of liquid through the medium or even stagnant regions which remain purely-diffusive. Despite numerous theorectical, experimental and numerical studies the transient and asymptotic behaviour of dispersion in porous media is not completely understood. In particular, the influence of stagnant zones with respect to the actual mesoscopic and macroscopic flow field heterogeneity of the medium has found little attention in theory and experiment. We have studied diffusion-limited mass transfer (1), transient and asymptotic longitudinal dispersion in single-phase liquid flow through a fixed bed made of spherical, permeable (porous) particles, covering several orders of characteristic time and length scales associated with fluid transport. The observed behaviour was contrasted to the corresponding fluid dynamics in a random packing of equally sized impermeable (nonporous) spheres with interparticle void fraction of 0.37. Experimental data for Pe up to 100 were obtained by pulsed field gradient NMR and were complemented by numerical simulations employing a hierarchical transport model with a discrete (lattice-Boltzmann) interparticle flow field using computer generated models of the interparticle pore space (2). Finite-size effects in the simulation associated with the spatial discretization of support particles or the dimension and boundaries of the bed were minimized and the simulation results are in reasonable agreement with experimental results. We conclude that the intraparticle liquid holdup clearly dominates over contributions caused by the intrinsic flow field heterogeneity and boundary-layer mass transfer.

Janez Stepisˇnik Physics Department, FMF, University of Ljubljana and J. Stefan Institute, Jadranska 19, 1000, Ljubljana, Slovenia The diffraction-like effect of spin echo at the diffusion measurement in porous media1 conveys information about pore morphology. Phenomena was analysed with the use of characteristic functional for the stochastic motion. Its cumulant expansion in the Gaussian approximation gives the spin echo as E共␶兲 ⬇ 冕Vei ␾ 共 ␶ ,r兲⫺ ␤ 共 ␶ ,r兲 dr, where the phase shift depends on the local velocity ␾(␶,r)⫽兰 o␶ F(t).具v(t,r)典 dt and the attenuation is related to the local velocity correlation function as ␤(␶,r) ⫽ 兰 0␶ 兰 t0 F(t).具v(t,r) v(t⬘,r)典 c .F(t⬘)dt⬘ dt, where the dephasing F(t) is the integral of the gradient. As long as the number of molecular impacts at walls is small, the usual approximations with the mean velocity as 具v(t,r)典 ⫽ 0 and with the correlation 具v(t,r) v(t⬘,r)典 c as a delta function are reasonable. At longer times, we need better approximation. The average of cumulants with the probability distribution from Fick’s diffusion equation2 provides distributions of phase shifts and attenuations in the volume of pore for any gradient sequence. Fig. 1 and Fig. 2 show the results for the diffusion between parallel planes, when PGSE sequence of sharp gradient pulses is applied. The integration over the space of pore gives the spin echo that exhibits diffraction-like patterns as shown in Fig. 3. The diffraction minima show dependence on gradient magnitude q ⫽ F ⫽ ␥␦G as well as on time. At short times, they are shifted toward larger q, and depend on the spin displacement as 2q 冑D/␲ ⯝ 2n␶. When the spin is starting to experience scattering on both opposite boundaries, the minima appear at value of qa ⯝ 2n␲$, thus conveying information about pore dimension a. The method explains the dependence of diffraction on time and type of sequence. It introduces the diffusive diffraction as an interference of the

References [1] Tallarek U, Vergeldt FJ, Van As H. 1999. Stagnant mobile phase mass transfer in chromatographic media: Intraparticle diffusion and exchange kinetics. J. Phys. Chem. B. 103: 7654 –7664. [2] Kandhai D, Tallarek U, Hluskou D, Hoekstra A, Sloot PMA, Van As H. 2002. Numerical simulation and measurement of liquid hold-up in biporous media containing discrete stagnant zones. Phil. Trans. R. Soc. Lond. Ser. A 360: 521–534.

A new view of the spin echo diffusive diffraction on porous structures

0730-725X/03/$ – see front matter © 2003 Elsevier Inc. All rights reserved.

Figure 2.

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Figure 3. phase shifts caused by the reflecting flow of spins scattered at the boundaries, when their displacements equal the phase grating created by applied gradients. This approach also enlightens the measurement of transport properties by the spin echo, particularly in the systems, where the molecular motion is constrained by structure or configuration.

broadened for gallium within porous matrices and NMR linewidths are larger for 69Ga than for 71Ga. Moreover, the NMR linewidth against the ppm frequency scale increases with decreasing magnetic field, what corresponds to the quadrupolar nature of line broadening as in viscous liquids. NMR lines are also broadened for confined liquid indium. The remarkable enhancement of the quadrupolar relaxation rate as well as its dependence on the magnetic field show that the spectral densities of the electric field gradient correlation function which determine quadrupolar spin relaxation in confined gallium are strikingly increased and the extreme narrowing approximation is no longer valid. The results obtained for confined gallium as well as for confined indium are consistent with the assumption about strong increase in the correlation time of the electric field gradients fluctuations, which reflects remarkable slowing down atomic dynamics in nanopores. The estimates were made for the correlation time in pores, which depended on pore sizes.

References [1] Charnaya EV, Loeser T, Michel D, Tien C, Yaskov D, Kumzerov Yu A. Phys Rev Lett 2002;88:097602

References [1] Callaghan PT, Coy A, MacGowan D, Packer KJ, Zelaya FO. Nature 1991;351:467–9 [2] Duh A, Mohoricˇ A, Stepisˇnik J. Mag Res 2001;148:257– 66 [3] Stepisˇnik J, Duh A, Mohoricˇ A. To be published.

Spin relaxation enhancement in liquid gallium and indium confined within nanoporous matrices E. V. Charnayaa, D. Michelb, C. Tienc, Yu. A. Kumzerovd aInstitute of Physics, St. Petersburg State University, St. Petersburg, Petrodvorets, 198504 Russia bFaculty of Physics and Geosciences, University of Leipzig, Leipzig, D-04103 Germany cDepartment of Physics, National Cheng Kung University, Tainan, 70101 Taiwan dA. F. Ioffe PhysicoTechnical Institute RAS, St. Petersburg, 194021 Russia First studies of nuclear spin-lattice relaxation and lineshape in liquid gallium and indium confined within random and quasi-regular pore networks of porous glasses and artificial opals are presented. It is shown that drastic enhancement of the relaxation rate occurs for confined liquid gallium and indium which can be treated as a result of the rise in the quadrupolar contribution which follows the strong increase in the spectral densities at the Larmor frequency of the electric field gradient fluctuations and might evidence the remarkable slowing-down in atomic mobility. The measurements were carried out using Avance400, MSL500 and MSL300 Bruker NMR spectrometers at room temperature for confined gallium and using an Avance400 spectrometer at 420 K for confined indium, the freezing transitions for metals within nanopores are lowered compared to that in bulk. The inversion recovery procedure was used to get data on spin-lattice relaxation. The spin magnetization restoration curves obtained for both gallium isotopes, 69Ga and 71Ga, and for indium isotope 115In showed remarkable enhancement in the relaxation rate compared to relevant bulk metals. The following main features can be noticed in data for gallium which contrast with those for bulk melt [1]: relaxation in the same field and in the same sample is noticeably faster for the 69Ga isotope with greater quadrupole moment and smaller gyromagnetic ratio; the relaxation rate visibly depends on magnetic field for gallium within porous glasses. The fact that relaxation is faster for the isotope with larger quadrupole moment shows that the quadrupolar contribution dominates longitudinal relaxation in confined geometry contrary to the bulk case. This is also valid for transverse spin relaxation as can be seen from lineshapes. While NMR lines for both gallium isotopes are narrow and coincide for bulk, they are noticeably

PFG NMR evidence for different apparent tortuosity factors in the Knudsen and bulk regimes of diffusion in a bed of NaX crystals O. Geier, S. Vasenkov, J. Ka¨rger Department of Interface Physics, University of Leipzig, Linne´str 5, D-04103, Leipzig, Germany Pulsed field gradient NMR was applied to study the ethane diffusion in beds of NaX zeolites for displacements, which are orders of magnitude larger than the size of the individual crystals. In order to probe the self-diffusion in the bulk and in the Knudsen regime the measurements were performed in a wide temperature range (193 K– 413 K). The transition from the Knudsen to the bulk regime occurs with increasing temperature as a consequence of temperature dependence of the fractions of the molecules in the gaseous and adsorbed phases. All measurements were carried out using the home built PFG NMR spectrometer FEGRIS 400 operating at a 1 H resonance frequency of 400 MHz [1]. To rule out disturbing effects which are caused by internal field gradients together with the standard stimulated echo sequence also the 13-interval bipolar [2] PFG pulse sequence was employed. Here, we report for the first time the direct experimental evidence that the apparent tortuosity factor in zeolite beds may be significantly larger in the Knudsen regime than in the bulk regime. The tortuosity factors were obtained by comparison of the measured diffusivities with those calculated using simple gas kinetic theory. The difference in the apparent tortuosity factors is not surprising in view of the different diffusion mechanisms in the Knudsen and in the bulk regimes. The reported results are in qualitative agreement with recent findings of dynamic MC simulations of gas diffusion in various porous systems [3,4]. The detailed explanation of the obtained results remains to be the subject of future research.

References [1] Galvosas P, Stallmach F, Seiffert G, Ka¨rger J, Kaess U, Majer G. Generation and application of ultra-high-intensity magnetic field gradient pulses for NMR spectroskopy. J Magn Reson 2001;151:260 [2] Cotts RM, Hoch MJR, Sun T, Markert JT. Pulsed field gradient stimulated echo methods for improved NMR diffusion measurements in heterogeneous systems. J Magn Reson 1989;83:25 [3] Burganos VN. Gas diffusion in random binary media. J Chem Phys 1998;109:6772 [4] Tomadakis MM, Sotirchos SV. Ordinary and transition regime diffusion in random fiber structures. AIChE J 1993;39:397

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

MRI of glue curing and water transport through glued wood layers G. Bennett,a H. Berglind,b O. Lindgren,b P. J. McDonalda aSchool of Physics and Chemistry, University of Surrey, Guildford, Surrey, Sweden, b Tratek, Swedish Institute for Wood Technology Research, Box 5609, S-114 86, Stockholm, Sweden Wood products have been estimated to account for over 9000 MEURO per annum within the european community of which around 1400 MEURO is attributed to glues and composite boards. The manufacture of composite boards is a multistep process of which hardening time is a key parameter. The glue must have enough time to cross-link and diffuse into the porous structure of the wood and the solvent must be sufficiently evacuated or the joint will be mechanically weakened. Moisture ingress into these boards may be retarded by the glue or conversely the adhesive is degraded. This latter process leads to a reduction in structural integrity, warping or complete failure of the product. Magnetic Resonance Imaging has been used to study the glue curing process between wood pieces and the water resistance of cured glue lines. Spin-echo Fourier transform methods are used with a high gradient (17 T/m) pernament magnet to produce profiles from a surface coil1. These profiles have a 15 mm spatial resolution and around 5 min temporal resolution. MRI has the advantages that the measurement is close to the real conditions encountered and is non-invasive. The high spatial resolution results in a very well defined signal origin so that different water types may be distinguished. The high temporal resolution allows curing and water ingress rates to be determined.

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The decay of the intensity and thickness of the glue line can be related to the evacuation of solvent and the curing of the glue. Whilst the changes in intensity and thickness of the signal from the wood layer gives information about the water distribution in the wood. The top figure (Fig. 1) shows the decrease in glue line intensity over time for three different types of hardners mixed with urea formaldehyde. The figure in the centre shows the total thickness of the wood and glue layer as the glue cures. This initially decreases as the water is absorbed into the pores of the wood and the glue line shrinks. At longer time the slower mechanism of water transport from the pores into the wood fibres creates wood swelling and an increase in thickness. Profiles measured while one side of the glued layer is exposed to water show the water resistance and or transport through the glued layer. An example of profiles measured for two wood layers glued with melamine urea formaldehyde is shown in the bottom figure. The peak at 200 mm is a standard marker, followed by the lower piece of wood (200 – 800 mm). A water reservior is seen at 1400 –1600 mm. Between 800 and 1400 mm is the wet wood layer getting progressively wet with increasing time. The three profiles are measured at 20 (black), 100 (grey) and 1400 min (dashed) and show no transport of water through the glue layer during this time. Two different types of wood are studied, Pine and Spruce, along with a range of wood glues including polyvinyl acetate, urea formaldehyde and phenolic resorcinol resins. These measurements provide information which will allow suppliers and manufacturers of wood and related products to improve the performance of their product or increase the efficiency of their process.

References [1] Glover PM, Aptaker PS, Bowler JR, Ciampi E, McDonald PJ. A novel high-gradient pernament magnet for the profiling of planar films and coatings. J Mag Reson 1999;139:90 –7

A new approach for probing the fractal pore geometry of sandstones by PFG-NMR studies Hansgeorg Pape Joachim E. Tillich Manfred Holz Applied Geophysics, RWTH Aachen, Lochnerstrabe 4 –20, D-52056 Aachen, Germany Institut fu¨r Physikalische Chemie, Universita¨t Karlsruhe, Kaiserstra␤e 12, D76128 Karlsruhe, Germany A good knowledge of pore space properties of sedimentary rocks is a prerequisite for the exploitation of hydocarbon reservoirs, as well as heat mining. After all, the interest is directed to the rock property permeability k which allows to calculate fluid flow. A fundamental expression for the permeability k of a porous medium is given by the modified KozenyCarman equation: k ⫽ 共1/8兲共 ␾ /T hydr兲共r eff兲 2

Figure 1.

where ␾ is the porosity, Thydr is the hydraulic tortuosity, and reff is the effective hydraulic pore radius. The names of these parameters point out that they are based on a geometrical model. Such a model can be applied to several physical methods of investigation, which allow to determine the geometrical parameters separately. Pulsed-field-gradient-nuclear magnetic resonance (PFG-NMR) is a method to determine pore space properties such as tortuosity and pore radius from measured time-depending self-diffusion coefficient D(⌬). As a first approach the Pade´ approximation, combining the short-time behaviour with the long-time asymptotic value of D(⌬)/D0 (where D0 is the bulk diffusion coefficient), was applied for determining the surface-to-pore volume ratio S/Vpor, which is related to reff, and the tortuosity T. As this method is based on interpolation, we tried to simulate the time dependence of D(⌬) based on physical principles and geometrical pore space models. The short time behaviour of the D(⌬)/D0 curve could best be simulated by a representive oblique and fractal bent capillary model. Porous media with relatively large tortuosity values could be best explained by a repre-

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sentative constricted capillary model, which was combined with the previous model. The novel approach was compared with the Pade´ approximation and tested with data from literature. For porous media with low tortuosity values and simple geometry such as glass bead packings, both methods are in good accordance and give similar results. In sedimentary rocks the new method is able to give some more details of pore geometry. However, the main advantage shows in porous media with fractal geometry or with constricted pores where the D(⌬)/D0 curves deviate in shape from simple two point Pade´ approximation curves.

Comparison of dipolar interaction refocusing techniques for MRI applications in porous media M. Terekhov, D. Ho¨pfel Institut fu¨r Innovation und Transfer (IIT)/Sensorsystemtechnik; University of Applied Sciences, Karlsruhe, Germany For the investigation of the structural and phenomenological properties of porous materials with magnetic resonance imaging (MRI) methods the achievable spatial resolution is of great importance. To image the spatial distribution of the spin density, the NMR free induction decay signal is encoded in k-space conjugated to the real r-space. The components of k-space are determined by magnetic field gradients Gi and corresponding encoding time ␶i as: ki ⫽ ␥ Gi␶i, where i ⫽ x,y,z, and ␥ is gyromagnetic ratio. The maximal value of k corresponds to the minimal possible value of the encoded volume cell element (voxel) ⌬rmin, i.e. spatial resolution: ⌬r i(min) ⫽ 1/(N i ␥ G i ␶ i ), where N i is the number of voxel in corresponding spatial direction. Thus, the requirements for a good spatial resolution are: (i) a high gradient strength with fast switching rate (technically restricted) and/or (ii) as long as possible encoding period ␶ i . The main problem of the proton imaging of rigid solid materials is that the strong dipolar interactions lead to the significantly wide spectral lines (⬎20 KHz). This results in relatively short (less than 50 ␮s) lifetime of the coherences that restricts drastically possible encoding period ␶i and, therefore, decreases the signal-to-noise ratio and the achievable spatial resolution. The Hahn spin-echoes, which are used to prolong the encoding period in liquid imaging are not effective in solids, where the bilinear interactions like dipolar or quadrupolar are not averaged by molecular motions. To improve the encoding efficiency, taking into account the limitations arisen from the magnetic field gradients strength and switching rate technical restrictions, two strategies are possible. The first is the artificial increasing of the lifetime of coherences: multi-pulse and multi-quantum line narrowing methods or magic angle spinning (MAS). The second is using a time-reverse pulse sequences like solid-echo, Jeener-Broekart echo, and “magic sandwiches” to refocus the dipolar order coherences and to increase, in that way, the efficient duration of the encoding. Different “pure phase-encoding” imaging techniques (JEPHI, MEPSI, etc) based on the dipolar interactions refocusing pulse sequences were proposed by Kimmich et al [1] to overcome the above mentioned restrictions of standard solid imaging methods like “Single Point Imaging” (SPI). These methods provide the elongation of the possible encoding period up to the factor 100 without incoherence losses (and therefore give a good signal-to-noise ratio) that makes them very attractive for the 3D solid imaging. However, the intrinsic artifacts caused by rf-pulse inhomogeneity (“zero peak artifact”, “scaled image artifact”) and superposition of the rf-irradiation with magnetic field gradients (inharmonic spatial encoding) [2], which could not be removed completely in each case, restrict the applicability of these methods. Due to the sufficient amount of the experimentally relevant factors, depending on (a) NMR - sample properties (T1,T2*,T1␳,⌬␴ ), (b) technical characteristics of the available hardware and (c) desirable resolution and experiment time, different basic time-reversing methods have to be used to endow with the best image quality in each special case. In the presented work the comparison of the several types of dipolar interaction refocusing pulse sequences and its modifications have been performed to find the optimum conditions for the imaging investigations in

different kinds of porous media. The influence and practical relevance of the different parameters on the image quality was tested for each method. The results obtained in this investigation can be helpful for choosing and customization of the most suitable imaging techniques to characterize the structure and phenomena of the porous media objects [3].

References [1] Demco, Hafner, and Kimmich. Journal of Magnetic Resononance. 96, 307–322 (1992). [2] Demco, Hafner and Kimmich. Journal of Magnetic Resononance. 94, 333–351 (1991). [3] Fang Z, Ho¨pfel D. Mag Reson Imag 2001;19:501–3

MRI study of swelling kinetics of HPMC containing tetracycline hydrochloride Jadwiga Tritt-Goc, Joanna Kowalczuk, Narcyz Pis´lewski Institute of Molecular Physics Polish Academy of Sciences, M. Smoluchowskego 17, 60 –179 Poznan´, Poland Hydroxypropylmethylcellulose (HPMC) has focused much attention as a hydrophilic matrix for sustained release formations. When exposed to water or body fluids, the polymer forms a gel layer around the tablets and greatly influences the dissolution and diffusion of the drug. The investigation of the fluid ingress into HPMC matrix was the subject of our previous study [1,2]. In the present study, we observed the behavior of gel layer thickness in HPMC matrices loaded with increasing amounts of soluble and colored drug tetracycline hydrochloride. The main goal of this work was to determine how the drug loading affected the swelling properties of the matrix. The method used was Magnetic Resonance Imaging. On the typical images of time-resolved diffusion of the solvent into an HPMC matrix the “swelling front” that separates the rubbery region and the glassy region of the polymer is clearly visible on the images. On the basis of such images taken at different times of immersion of sample into the solvent, the gel layer thickness was determined for matrices containing different percentages of the drug and for pure HPMC matrix. The influence of drug loading on an HPMC matrix swelling properties is clearly visible on the images. The sample with the highest amount of drug (33%) showed the fastest movement of the swelling front. A low amount of polymer in the matrix rendered the matrix more sensitive to solvent penetration.

Acknowledgments This work was supported by the Polish Committee for Scientific Research under Project no. 4P0 5F 010 19

References [1] Tritt-Goc J, Filipowski Z. Use of MRI to study transport of water in polymer. Mol Phys Rep 2001;34:55. [2] Tritt-Goc J, Pis´lewski NMagnetic resonance imaging study of the swollen kinetics of hydroxypropylmethylcellulose (HPMC) in water. J Controlled Release 2002;80(1–3):797

On the fate of non-aqueous solvents in a hydrating cement matrix Nikolaus Nestle1,2, Petrik Galvosas2, Frank Stallmach2, Christian Zimmermann3, Marwan Dakkouri3, Jo¨rg Ka¨rger2 1TU Mu¨nchen, IWC, Marchioninistra␤e 17, D-81377 Mu¨nchen, Germany 2 Universita¨t Leipzig, Abteilung Grenzfla¨chenphysik, Linne´strabe 5, D04103 Leipzig, Germany 3Universita¨t Ulm, FB Chemie, D-89069 Ulm, Germany

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 The impact of non-aqueous solvents onto the hydration kinetics of cement and the distribution of these liquids in the resultant cement stone is of practical relevance in the context of waste solidification. Furthermore, the distribution of the solvents in the hydrating cement matrix also may lead to general insights into the role of liquid-liquid phase boundaries on the microscopic scale in interface growth processes on short length scales. NMR relaxometry has been used for quite a long time as a tool for studying cement hydration kinetics via the water dynamics [1]. Due to recent improvements in PFG NMR capabilities, is has also become possible to study the water-self-diffusion in hydrating cement matrices during the first few days of hydration [2]. In studies of cement hydration in the presence of non-aqueous solvents via NMR 3 and synchrotron tomography 4, surprizing differences in the behaviour of aromatic and aliphatic solvents were observed. On the basis of these findings, we have conducted further experiments of the relaxation and diffusion behaviour of the solvent phase. These studies reveal an additional formation of diffusion barriers in all solvent phases studied. In the case of aromatics, a similarly strong decrease in the self-diffusion coefficient was observed as for water while the decrease in the other solvents was found to be less pronounced. The findings suggest that the solvent phase is partially dispersed into a fine network of mazelets throughout the cement stone matrix. In the case of aromatic solvents, all the solvent is dispersed like that for solvent quantities up to 0.066 mL/g cement at a water/cement ratio of 0.33 mL/g.

References [1] Blinc R, Burgar M, Lahajnar G, Rozmarin M, Rutar V, Kocuvan I, Ursic J. J Amer Ceram Soc 1978;61:35 [2] Nestle N, Galvosas P, Geier O, Zimmermann C, Dakkouri M, Ka¨rger J. J Appl Phys 2001;89:8061 [3] Nestle N, Zimmermann C, Dakkouri M, Niessner R. Environ Sci Tech 2001;35:4953 [4] Butler LG, Owens JW, Cartledge FK, Kurtz RL, Byerly GR, Wales AJ, Bryant PL, Emery EF, Dowd B, Xie X. Environ Sci Technol 2000; 34:3269

NMR diffusion-relaxation in three-phase fast exchange system S. Wonorahardjo1, I. Ardelean2, C. Mattea, R. Kimmich Universita¨t Ulm, Sektion Kernresonanzspektroskopie, Albert Einstein Allee 11, Germany Reorientation Mediated by Translational Displacement (RMTD) relaxation mechanism as a consequence of Bulk Mediated Surface Diffusion (BMSD), governs the dynamics in the inner polar surface of filled porous material. The confined adsorbate liquid exist in two homogeneous and rapidly exchanging phases and is known as the two phase fast exchange model. The effective displacement is described by Cauchy distribution which indicates anomalous diffusion in topologyically two-dimmension surface space. When the porous system is partially filled, the molecules in gas phase will contribute to the dynamics in the interface depending on the strength of interaction, the pore size, and the phase distribution. Some proton diffusion and relaxation experiments of water (H20) and cyclohexane C6H12) in Vycor Porous Glass (VPG) show the vapor contribution in the surface dynamics. The liquid content in fact plays an important role in the transition condition, especially in low field masurement where the correlation time would be very long. Vapor Mediated Surface Diffusion (VMSD, in addition to BMSD) in low liquid content systems is to be considered further, also for system which has no strong molecule-surface interaction.

Corresponding author. Universitaet Ulm, Sektion Kernresonanzspektroskopie, 89069, Ulm, Germany

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1 Current address: Department of Chemistry, Universitas Negeri Malang, Indonesia. 2 Current address: Department of Physics, Cluj Technical University, Romania.

NMR-studies of the dynamics of guest molecules in Mesoporous Silica G. Buntkowsky1, E. Gedat1, J. Albrecht1, H. H. Limbach1, A. Schreiber2, G. H. Findenegg2 1Freie Universita¨t Berlin, Institut fu¨r Chemie, Takustrabe 3, 14195 Berlin, Germany 2Technische Universita¨t Berlin, Iwan-N.-Stranski-Laboratorium fu¨r Physikalische und Theoretische Chemie, Strabe des 17. Juni 112, 10623 Berlin, Germany Dynamical properties of guest molecules in mesoporous silica are investigated with 2H-solid state and 1H-strayfield NMR spectroscopy. In the first part of the study1 Benzene-d6 confined in the hexagonal ordered cylindrical pores of mesoporous silica SBA-15 (pore diameter 8.0 nm) is studied by low temperature 2H solid state NMR spectroscopy in the temperature range between 236 K and 19 K and compared to bulk benzene-d6. At all temperatures below the freezing point the spectra of benzene in the silica show the co-existence of two states with temperature dependent intensity ratios. This behavior is the result of a Gaussian distributions of activation energies for the rotational jumps inside the pores. From the pore volume and the filling factor a thickness of four molecular layers of this surface phase is estimated. In the second part of the study2 the diffusion of pyridine confined in mesoporous silica MCM-41 (dpore ⫽ 3.3 nm) is studied with Stray Field Gradient NMR diffusometry as a function of the filling factor of the mesopores at room temperature, employing a home built SFG setup. The translational diffusion of pyridine in MCM-41 is found to be anisotropic. The parallel diffusion coefficient depends strongly on the filling level of the guest liquid inside the pores. For a filling level of 25%, which corresponds approximately to a mono-molecular layer of pyridine molecules hydrogen bond to surface -SiOH groups, a parallel diffusion coefficient of D㛳⫽1.0 ⫻ 10⫺9m2/s is found, which is slower than the diffusion coefficient of the bulk liquid (D ⫽ 1.6 ⫻ 10⫺9m2/s). For higher filling factors the parallel diffusion coefficient increases. Employing additional 15 N-MAS data of the pyridine inside the mesopores a microscopic model of the diffusion is proposed, which depends on the exchange of the slowly diffusing hydrogen bound surface pyridine molecules with fast diffusing free pyridine molecules inside the pores.

References [1] Gedat E, Schreiber A, Albrecht J, Shenderovich I, Findenegg G, Limbach H.-H, Buntkowsky G. J Phys Chem 2002; accepted for publication. [2] Gedat E, Schreiber A, Findenegg GH, Shenderovich I, Limbach HH, Buntkowsky G. Magn Reson Chem 2001;39:149

A magnetic resonance imaging study of dense nonaqueous phase liquid dissolution from angular porous media Changyong Zhang, Charles J. Werth, Andrew G. Webb University of Illinois at Urbana-Champaign, Urbana-Champaign, Illinois, USA Magnetic Resonance Imaging (MRI) was used to determine the effects of pore-scale heterogeneity on the dissolution of a nonaqueous phase liquid in water-saturated flow-through columns (1.2 cm in diameter) packed with either 500 or 1000-micron diameter angular silica gel (referred to as SG500 and SG1000, respectively). Columns were initially contaminated with 1, 3, 5-trifluorobenzene (TFB) at residual saturation. A 3D slab-selective spinecho imaging sequence was used to acquire 19F images of the entrapped TFB at a frequency of 188.592 MHz. For all three-dimensional images, a field-of-view of 1.5 ⫻ 1.5 ⫻ 1.5 cm3 was acquired with a data matrix of 256 ⫻ 64 ⫻ 64 complex data points. A repetition time (TR) of 500 ms and

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echo time (TE) of 9 ms were used with two signal averages. Images were acquired at selected time points during dissolution (every 2 to 5 h) while the column was being purged with water. The acquired 3D time-domain data (256 ⫻ 64 ⫻ 64) were zero-filled to 256 ⫻ 256 ⫻ 256, baseline corrected, inverse Fourier transformed and the magnitude of the complex data taken. An algorithm using minimum size and signal thresholding was developed to identify the location, surface area and volume of each DNAPL blob. Imaging results show that the specific DNAPL surface area (at) is proportional to the DNAPL volumetric fraction (␪n), and that values for both of these parameters decrease during dissolution. Imaging results were used to calculate overall (expressed as the modified Sherwood number, Sh29) and intrinsic (expressed as the apparent Sherwood number, Shapt) mass transfer rate coefficients during dissolution. Sh⬘ was found to first increase or stay the same and then decrease with decreasing ␪n, while Shapt steadily increased with decreasing ␪n. This behavior is attributed to the creation of new flow paths during dissolution, an effect that may be more significant in angular porous media.

Magnetic resonance imaging of fractures in crystalline rock cores by spin echo and single point imaging Makoto Yamaguchi1, Takahiro Ohkubo2, Kazunori Suzuki1, Yasuhisa Ikeda2 1Institute of Research and Innovation, Kashiwa, Chiba 277-0861, Japan 2Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan Fluid flows in rock fractures have been paid much attention from various aspects including petroleum recovery or migration of radioactive nuclides from geological disposal sites. Model fractures have been studied extensively both experimentally and theoretically to clarify how the flows and migration of solutes are affected by local variations in apertures in a single fracture. While magnetic resonance imaging has been a promising method to measure local flow properties of opaque materials, there are few studies on imaging of fractures in igneous rocks: They contain paramagnetic and/or ferromagnetic minerals and their very large magnetic susceptibilities severely distort NMR images. As for the effect of magnetic susceptibility inhomogeneity, various new methods have been developed in recent years for medical and material imaging to decrease image distortion. This presentation is our preliminary result on NMR imaging to obtain less distorted images of fractures in crystalline rock cores. Cylindrical rock core samples (maximum diameter ⫽ 35 mm) were made from Inada granite and they were cut or fractured vertically. Samples were immersed in aqueous copper sulfate solution and 1H NMR signals were measured at 300MHz. Inada granite contains small amounts of biotite and hornblende, which are both paramagnetic. In order to examine the effect of magnetic susceptibility inhomogeneity we have applied both spin echo and single point imaging methods. In the case of spin echo method including slice-selective 2DFT and 3DFT imaging, increased magnetic field gradient strength along the frequency encoding direction decreased distortion in obtained images. Fast spin echo method resulted in less distorted images compared with the cases of single or multi spin echo methods. As for single point imaging, both basic SPI and single point ramped imaging with T1 enhancement (SPRITE) methods were studied. Cylindrical shape of samples was distorted by regions near paramagnetic mineral grains where very weak signals due to very short T2*. The effect of both gradient strength and sampling time to minimize distortion in images will be discussed.

Fig. 1. 1HC MAS NMR spectra of dehydrated samples of AICI1/MCM41(a), AJCI1MCM-41 loaded with pyridine-d1 (b) and AICI1/MCM-41 loaded with ammonia (0.15 mmol/g)(c). lites, however, the weak acidity of MCM-41 materials limits their valuable application in chemical technology. Different methods have been devised to introduce strong acid sites into MCM-41. However, to the best of our knowledge, preparation and unequivocal identification of strong Bronsted acid sites in MCM-41 mesoporous materials have not been reported. Here, a method is described to modify siliceous MCM-41 in vacuum with sublimated AlCl3 at a temperature of 403 K. Strong Bronsted acid sites were identified in the modified product AlCl3/MCM-41 by multi-nuclear solid-state NMR spectroscopy. In the 1H MAS NMR spectrum of the siliceous MCM-41 (not shown), only a single signal occurs at 1.8 ppm with a broad tail at the low-field side, due to isolated and hydrogen-bonded silanol groups. The 1H MAS NMR spectrum of AlCl3/MCM-41 (Fig. 1a) consists of signals at 0.9, 3.0 and 6.0 ppm. The signal at 0.9 ppm is cause by hydroxyl groups connected to aluminum species [3]. AlOH groups involved in hydrogen bondings are responsible for the signal at 3.0 ppm [3]. The signal at 6.0 ppm could be caused by strongly acidic OH groups formed during the treatment with aluminum chloride: adsorption of pyridine-d5 leads to the formation of pyridinium ions (12.5 ppm 3) accompanied by the disappearance of the signal at 6.0 ppm (Fig. 1b). Additionally, the Bronsted acidity of the corresponding species is evidenced by the formation of ammonium ions (6.3 ppm [3]) after adsorption of ammonia (Fig. 1c). An investigation of the acid strength of the Bronsted acid sites formed on AlCl3/MCM-41 was performed by adsorption of 13C-2-acetone. The isotropic chemical shift of the 13C MAS NMR signal of carbonyl atoms is sensitive concerning the interaction between the carbonyl groups of acetone molecules and acid sites. A downfield shift of this 13C MAS NMR signal indicates an interaction between stronger acid sites and acetone molecules and vice versa [4,5]. After adsorption of 13C-2-acetone on AlCl3/MCM-41, 13C MAS NMR signals appeared at 242 and 245 ppm and confirmed the existence of strong Bronsted acid sites. In contrast, adsorption of 13C-2-acetone on acidic zeolite H-ZSM-5 leads to a 13C MAS NMR signal with a chemical shift of 223 ppm only [4,5]. Based on Ref. [6], the local structure shown in Scheme 1, right, with X ⫽ Cl is proposed to be responsible for the strong Bronsted acidity of AlCl3/MCM-41. This local structure is analogous to that of bridging OH groups in acidic zeolites but with enhanced acid strength due to the presence of more electronegative chlorine atoms. The 27Al MAS NMR spectrum of AlCl3/MCM-41 consists of signals at 76 and 86 ppm caused by

Preparation of strong br␾nsted acid sites on MCM-41 by a low temperature treatment with aluminum chloride Mingcan Xu, Michael Hunger Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany Due to the uniform mesopores and the large specific surface area [1,2], mesoporous MCM-41 materials find an increasing interest for versatile applications in adsorption, chemistry and materials science. Unlike zeo-

Scheme 1. Local structures of aluminum species in AICI3/MCM-41.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 tetrahedrally coordinated aluminum species (Scheme 1) and a signal at 35 ppm attributed by Drago et al. [6] to hydroxychloroaluminum species.

References [1] Yanagisawa T, Shimizu T, Kuroda K, Kato C. Bull Chem Soc Jpn 1990;63:992 [2] Kresge CT, Leonovicz ME, Roth WJ, Vartulli JC, Beck JS. Nature 1992;359:710 [3] Hunger M. Catal. Rev Sci Eng 1997;39:345 [4] Biaglow AI, Gorte RJ, Kokotailo GT, White D. J Catal 1994;148:779 [5] Xu EJ, Munson JF, Haw J. Am Chem Soc 1962;116:1962. [6] Drago RS, Petrosius SC, Chronister CW. Inorg Chem 1994;33:367

Comparison of electric current and pressure-driven flow in random site-percolation model objects: numerical simulation and NMR experiments Markus Weber, Rainer Kimmich Sektion Kernresonanzspektroskopie, University of Ulm, Ulm, Germany Besides hydrodynamic flow and diffusion, electric current in porous media is of major interest as a further paradigm of percolation theory. The objective is to compare viscous flow (subject to inertia) with inertialess electric current (subject to Ohmic resistance) in the very same porous system. Percolation model objects were fabricated based on random-number generated templates. The pore space was milled in polystyrene sheets and filled with liquids and electrolyte solutions. External pressure and potential gradients permitted us to measure velocity as well as current density maps. The latter were recorded with the aid of NMR current density mapping [1]). In this way the spatial distribution of electric currents in 60 ⫻ 60 two-dimensional site-percolation model objects were visualized [2]. The experimental results were reproduced by numerical simulations based on the standard potential theory. Fig. 1 shows the experimental transport patterns for hydrodynamic flow and electric current. Characteristic deviations arise from the different dependences of the flow and current resistance on the pore channel width. Histograms of the velocity and current density maps indicate these differences in a more quantitative way. The experiments and the numerical calculations to be described in this paper demonstrate that material and immaterial transport properties can directly be related to each other very specifically.

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References [1] Scott GC, Joy MLG, Armstrong RL, Henkelman RM. J Magn Reson 1992;97:235; Sersa I, Jarh O, Demsar Franci. J Magn Reson A 1994; 111;93. [2] Weber M, Kimmich R. Phys Rev E. 2002; submitted for publication.

Thermal convection in random-site percolation model objects: numerical simulation and NMR experiments Markus Weber, Andreas Klemm, Rainer Kimmich Sektion Kernresonanzspektroskopie, University of Ulm, Ulm, Germany Stationary thermal convection was investigated in two-dimensional 100 ⫻ 50 site percolation models with the aid of numerical simulations based on the finite volume method (FVM). Similar to the percolation threshold p c the Rayleigh-Be´nard percolation threshold p cRB was discovered as a new critical phenomenon. It reflects the transition of convection loops extended over the whole porous structure to loops of a local nature. The RayleighBe´nard percolation threshold is in the range p c ⬍ p cRB ⱕ 0.65. The critical Rayleigh number for a Rayleigh-Be´nard configuration without porespace restrictions indicates the onset of coherent flow. This is in contrast to porous media, in which coherent flow occurs at any bottom/ top temperature difference as a consequence of local horizontal temperature gradients arising due to the different heat conductivities in the matrix and in the fluid. We have studied this phenomenon as a function of the porosity and the bottom/top temperature difference. Velocity histograms above the Rayleigh/Be´nard percolation threshold display two different regions: In the vicinity of p cRB , the high-velocity part of the histograms can be described by an exponential function, whereas the low-velocity end appears to follow a power law (Fig. 1). In addition to the numerical investigations, NMR experiments have been carried out with the same percolation networks. Corresponding model objects were fabricated with the aid of a computer guided circuit board plotter. The porespace of the objects was filled with silicon oil and investigated with the aid of NMR velocity mapping. The data reproduce the numerical simulations only with respect to the flow patterns but also for the velocity distribution functions. Temperature maps were recorded in the same objects in addition based on the strong temperature dependence of the T1-relaxation of ethyleneglycol. That is, the local temperature gradients can be visualized in this way and can be compared with flow convective flow patterns caused by these gradients.

Fig. 1. Comparison between hydrodynamic flow and electrical current in a site-percolation model with a porosity of p ⫽ 0.7. a) NMR-velocity map v ⫽ 冑vx2 ⫹ vy2 b) NMR-electric current density map j ⫽ 冑jx2 ⫹ jy2 .

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Fig. 1. Comparison between simulation and NMR-experiment: Thermal convection in a site-percolation model with a porosity of p ⫽ 0.7. a) NMR- velocity map v ⫽ 冑v⬘2 ⫹ vy2b) Simulation v ⫽ 冑v⬘2 ⫹ vy2.

References [1] Weber M, Klemm A, Kimmich R. Phys Rev Lett 2001;86(19):4302 [2] Kimmich R, Klemm A, Weber M, Seymour J. Mat Res Soc Symp Proc 2002;651:2.7.1

A generalisation of the thermoporosimetry Gibbs-Thomson equation for arbitrary pore geometry J. B. W. Webber School of Physical Sciences, University of Kent, Kent, United Kingdom. We derive the thermoporosimetry Gibbs-Thomson equation from the fundamental thermodynamic processes and show that NMR cryoporometry and DSC thermoporosimetry both (like gas adsorption) give a measure of the ratio of pore volume to pore surface area. Thus one may now calculate the pore dimensions for a range of pore geometries, including slits. We give a brief history of the development of the thermodynamics of melting point depression and capillary condensation as considered by Prof. James Thomson in 1849, Sir William Thomson (his brother, later Lord Kelvin) in 1871, Josiah Willard Gibbs in 1875 and 1878, Prof. J.J. Thomson in 1888, and Defay et al. 1951, 1966. The thermoporosimetry Gibbs-Thomson equation has been given by Jackson and McKenna in 1990 in a form that relates the melting point depression of a crystal of a liquid in a pore to the diameter of the pore. However we show here that this is a simplified form. A new derivation of the thermoporosimetry Gibbs-Thomson equation applying a synthesis of the above approaches is given here, that derives a more general equation, and relates the melting point depression to the ratio of pore surface area to pore volume. This is applicable to a range of pore geometries. It is shown that for the often implicitly assumed ’infinite right cylindrical pores’ this expression reduces to a new form that simplifies to that given by Jackson and McKenna, but which has a higher accuracy.

NMR study of tert-butyl chloride confined to CPG L. Wasyluk, B. Peplin´ska, S. Jurga Institute of Physics, Adam Mickiewicz University, Umultowska 85, 61– 614 Poznan˜, Poland The molecular dynamics of tert-butyl chloride (TBC) confined to CPG of pore diameters of 75 and 250 Å was investigated by measuring linewidths, lineshapes and 1H, 2H spin-lattice relaxation times. Only two sharp phase transitions are reflected in T1 measurements in comparing to the three in the bulk sample. The temperatures of the phase transitions of confined TBC are depressed in comparison with bulk TBC by about 23 K for 75 Å CPG and by about 13 K for 250 Å CPG. The values of 1H, 2H relaxation time T1 shown in Fig. 1 are reduced indicating that the confinement strongly restricts molecular reorientation. In both CPG differing in pore size the two exponential magnetization recovery is observed in the temperature interval corresponding to the solid phase II. The confined liquid is considered as forming two distinct phases: a surface-affected liquid phase and a bulk liquid phase. The surface-affected phase of confined TBC, composed of molecules located at the pore surface, has a shorter spin-lattice relaxation times than the bulk liquid. In the solid phase III only one component of the 1H and 2H relaxation times T1 is found for 75 Å as well as for 250 Å CPG. The observed relaxation component is attributed to the bulk liquid phase of confined TBC. The minima of T1 assigned to the rotation of the tert-butyl group are shifted up, they become shallower and wider with decreasing of the pore diameter, reflecting the distribution of rotational correlation times. The 1H and 2H lineshape analysis of the confined sample reveals the existence of two components in solid phases II and III. The narrow component is superimposed on the broad one, and the relative intensity of the narrow component is larger for 75 Å than for 250 Å CPG.

Fig. 1. Temperature dependences of 1H and 2H relaxation times T1 for bulk TBC (solid circles), TBC confined to 75 Å CPG (solid and open triangles) and TBC confined to 250 Å CPG (solid and open squares).

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

NMR diffusion studies of translational properties of oil inside coreshell latex particles Helena Wassenius1,2,*, Magnus Nyde´n1, Brian Vincent3 1Department of Applied Surface Chemistry, Chalmers University of Technology, S-412 96 Go¨teborg, Sweden 2BIM Kemi AB, Box 3102, S-443 03 Stenkullen, Sweden 3Department of Physical Chemistry, School of Chemistry, University of Bristol, Cantock’s Close, Bristol, England BS8 1TS, United Kingdom Core-shell particles are of increasing interest. i.e. as drug delivery systems for controlled release products and for oxidation prevention applications. The colloidal properties of core-shell latex particles with a liquid core of hexadecane and a solid polystyrene shell have been studied with the Pulsed Field Gradient Spin-Echo (PFG-SE) NMR technique. As predicted by the q-space theory for molecules diffusing inside a spherical cavity, diffraction peaks were observed at the q-values expected from the q-space formalism. The weak appearances of these peaks are discussed in terms of particle size polydispersity, particle flow, wall relaxation effects and the influence of oil residing in the particle shell. The short-time diffusion behaviour of the core-shell particles was found to be roughly consistent with the hard sphere model. By changing the effective diffusion time a very strong dependence of the apparent oil diffusion coefficient was observed, and it was concluded that at long diffusion times the NMR echo decay provided the particle size and size distribution. At intermediate times the diffusion coefficient increased rapidly with decreasing diffusion times, and it was noted that in order to reach the value for the unrestricted oil motion sub-millisecond diffusion times must be used.

* Corresponding author. [email protected] (H. Wassenius)

Cell-to-cell coupling via plasmodesmata in plant roots: NMR-data Olga Volobuyeva1, Gennady Velikanov2 1Kazan State University, 420008, Kazan, Kremlevskaya, 18, Russia 2Kazan Institute of Biochemistry and Biophysics Russian Academy of Science, Kazan, Kremlevskaya, 18, Russia Plasmodesmata (PD) are transcellular bridges interconnect all cells of a plant body into supracellular symplastic continuity and contain internal (desmotubule) and outside tubes connecting accordingly vacuoles and cytoplasms of cells. Using NMR-method with pulse gradient of a magnetic field we have a tool allowing direct approach to study water transport via two PD channels in wheat roots. Measured spin-echo values can be reliably decomposed into three distinct components with corresponding coefficients of self-diffusion (CSD) of water molecules that correlated with sub-cellular and supra-cellular structure of a root. It has been demonstrated that two of these CSD values (D2 and D3) reflect water self-diffusion inside cytoplasmic (symplast) (D2) and vacuolar (endoplast) (D3) compartments and depend on the actual conductivity of corresponding transport channels of PD. Our NMR data support the existence the active regulation of gating of PD by ATP-dependent actin-myosin motility (results of experiments with cytoskeletal inhibitors - cytochalasin B and 2,3-butanedione monoxime; inhibitors of energy metabolism - antimycin A and sodium azide; and all network of plant signal system (experiments with ABA and A23187).

* Corresponding author. olga,[email protected] (O. Volobuyeva)

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A quantitative study of porosity classes in trabecular bone by MRRelaxation and MR-Cryoporometry P. Fantazzini1, C. Garavaglia1, J. Mitchell2, R. Viola3, J. H. Strange2 1 Univ. of Bologna, Dept. of Physics, Viale Berti Pichat 6/2, 40127 Bologna, Italy 2Centre for Materials Research, University of Kent, at Canterbury, Canterbury, United Kingdom. 3Univ. of Bologna, Dept. of ICMA, Viale Risorgimento 2, 40136 Bologna, Italy The interest in Magnetic Resonance studies of bone is increasing as new noninvasive MR Imaging methods are being developed to study bone microstructure and the effects of diseases such as osteoporosis. In a preliminary study [1], the feasibility and potential for the combined use of MR-Relaxation (MRR) of 1H nuclei and MR-Cryoporometry (MRC) [2] for the study of bone microstructure was demonstrated. The study has been extended to the quantitative characterization of particular classes of pore spaces in trabecular bone, with a special emphasis on the intratrabecular space where MRC is expected to be more sensitive. It has been shown [3] that from MRR it is possible to distinguish between the signal of water in the large inter-trabecular spaces and that in the smaller intra-trabecular spaces. This work provides solid validation of those results with the characterization of different structures in the bone pores for a large set of samples. MRC offers evidence for the existence of pores with diameters less than 2000 –3000Å in bone. MRR analysis [3] allows one to distinguish and quantify the fraction of pore volume in the inter- and intra-trabecular spaces in such a way that the bone volume fraction (BVF) can be determined. BVF is defined as the ratio of solid bone volume (including any intra-trabecular pore space) to total bone volume (including all pore space); it is a parameter usually determined by histomorphometric analysis, quantitative 3D X-Ray or MRI microtomography. In addition, our combined magnetic resonance methods allow one to measure the internal porosity of the trabeculae (⌽intra), defined as the ratio of intra-trabecular pore volume to the total volume occupied by the trabeculae. For the analysis cow femur samples were carefully cored and cleaned in order to remove any marrow and other natural fluids. MRR was performed at 20 MHz and 20 °C on samples dried under vacuum and then fully saturated with water. Quasi-continuous distributions of T1 in bone samples reflect the confinement effect on the water. All T1 distributions examined were bimodal, usually with a small tail going down to about 1 ms, indicating some very small pores. Because of the possibility3 of distinguishing between signals from inter-trabecular spaces (long T1 component) and signals from intratrabecular space, it is possible to evaluate the ratios of inter-trabecular and intra-trabecular pore volumes to total pore volume, Sinter/(Sinter⫹Sintra) and Sintra/(Sinter⫹Sintra). From these data BVF can be computed as BVF ⫽ 1⫺⌽Sinter/(Sinter⫹Sintra), where ⌽ is the total porosity, which can be determined by weighing the sample before and after water saturation. From these parameters the value of ⌽intraintra can easily be computed. The fraction Sintra/(Sinter⫹Sintra) obtained by MRR is consistent with the existence of pores with sizes less than 3000Å, as evaluated by MRC. On the same samples we obtained BVF values consistent with data from other sources and ⌽intraintra of the order of 30%. We do not know of any other method to determine ⌽intra in a simple and non-destructive way.

References [1] Fantazzini P, Viola R, Alnaimi S, Strange JH. Combined MR-Relaxation and MR-Cryoporometry in the study of bone microstructure. Magn Reson Imaging 2001;19:481– 4 [2] Strange JH, Rahman M, Smith EG. Characterization of porous solids by NMR. Phys Rev Letters 1993;71:3589 –91 [3] Fantazzini P, Brown RJS, Borgia GC. Bone tissue and porous media: Common features and differences studied by NMR relaxation. Presented at the Sixth International Meeting on MR Applications to Porous Media, Ulm, September 2002.

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Compositional and structural properties of fish feed by low field NMR Emil Veliyulin, Karl Osterhus, Claas van der Zwaag, Trond Singstad, Tore Skjetne SINTEF Unimed MR Center, 7465 Trondheim, Norway EWOS Innovation AS, 4335 Dirdal, Norway The quality of fish feed and the effectiveness of fish feed production processes are important issues for both suppliers and fish farmers. Fish feed consists of various protein sources, fat and water and is in the production process compacted to a pellet with a porous, semi-solid matrix that is saturated with fish oil. Some of the most important quality parameters of fish feed are protein, fat and water content as well as pore size distribution. A satisfactory combination of these characteristics is crucial for achieving a desirable growth rate, fat and protein content of farmed fish. We have recently developed several low field NMR techniques that can provide fast and cost efficient at-line quality control of fish feed. Determination of protein, fat and water content of raw materials and of fish feed pellets along with other characteristics were performed and compared to quantitative extraction methods as well as Near Infrared Spectral Analysis. The correlation factor between NMR and chemical extraction method was 0.997 for fat content determination, 0.996 for protein content and 0.8 for rest water. A combination of solid echo, spin echo and free induction decay NMR sequences provides with the information about the protein, fat, and rest water content in fish feed. Prior to the measurement the application has to be calibrated against several reference samples with known characteristics. An important advantage of the NMR technique is that the low field NMR response is independent of the microscopic properties of the raw materials used in the production (origin and type of fish oil and protein sources), being directly proportional only to the total quantity of the measured compound. Therefore it is not necessary to recalibrate the instrument if the raw materials are supplied from different environmental sources. Other advantages of low field NMR compared to standard chemical analysis and NIR are following it is quick, non-destructive, utilises no dangerous toxic solvents and it can be performed by ground-floor personnel. Another NMR technique that totally suppresses all the water signal, measuring only the total fat quantity can be applied to a wide variety of materials ranging from fish feed, fish, meat and milk products to rock cores. This NMR method discriminates between fat and water signal on a quantum mechanical level and should be applicable to practically any material, independently of its origin and mobility of the fat and water phases. The method is particularly useful for the study of systems containing considerable quantities of both water and fat (fish, milk, rock cores), where conventional NMR techniques might be inapplicable. Leakage of the fish oil from the porous matrix of fish feed is yet another serious problem to be addressed here. Such leakage usually causes unaffordable losses of the product value during the storage and transportation. Fish oil leaks predominantly from the largest pores and therefore is controlled by the pore size distribution of the pellet. It is demonstrated that measuring distributions of spin-spin relaxation times gives possibilities to estimate the leakage rate from fish feed on an early production stage, allowing to adjust production parameters in order to control oil leakage.

Flue gas cleaning of future power plants –fundamental investigations via MRI V. van Buren, R. Reimert Engler-Bunte-Institut, Bereich Gas, Erdo¨l und Kohle, Universita¨t Karlsruhe (TH), 76131 Karlsruhe, Germany A general approach to the application of Magnetic resonance imaging (MRI) in chemical engineering research is presented for the concrete example of the in-situ investigation in the kinetics of droplet separation in packed beds. Background of this research is the separation of slag droplets upstream of a gas turbine, which is one of the major engineering problems to be solved in the development of power plants based on pressurised pulverised coal combustion.

In the presented work the ability of MRI was exploited to visualise the internal structure and liquid distribution in the granular bed with spatial resolution. Non-invasive experiments were carried out in a cold lab scale separator arranged in the centre of a NMR magnet to investigate the droplet separation kinetics in granular bed filters. Experiments were made by using a Bruker 4,7 T (200 MHz) nuclear magnetic resonance tomograph with a vertical bore of 64 mm in diameter. The used pulse-sequence was similar to the spin-warp-sequence with phase encoding gradients. A siliconoil/airaerosol was used which simulates the slag/fluegas-aerosol of the power plant in mind. The experiments provide information about local separation, liquid and porosity distribution in the packed bed. Furthermore, MRI technique was used to measure the velocity distribution of the down flowing liquid in the granular bed. Dependent on several parameters as sphere diameter, ratio of granular bed to sphere diameter, superficial gas velocity and viscosity of the liquid fluid, data obtained from MRI experiments has been analysed in order to quantify their effects on droplet separation in granular beds. Finally, initial modelling results will be presented.

Pressurized gas magnetic resonance imaging for monitoring flow and particle deposition behaviors in Diesel Particulate Filters S. Tsushima1, S. Hirai1, Y. Yamamoto2 and Y. Nakasuji2 1Research Center for Carbon Recycling and Energy, Tokyo Institute of Technology 2 NGK Insulators, ltd. Recent advances on gas magnetic resonance imaging [1] has attracted much attentions to probe dynamic behaviors of fluids in industrial applications. However, gas magnetic resonance imaging techniques still cope with some of difficulties especially on its spatial resolution owing to low spin density in gaseous medium. In the engineering point of view, gas magnetic resonance imaging with high spatial resolution is needed to investigate actual flow systems. In this article, we shows a gas magnetic resonance imaging with relatively high spatial resolution using pressurized methane gas and a high pressure vessel that can be installed in high magnetic fields [2]. We applied this pressurized gas MRI to monitor flow and particle deposition behaviors in a Diesel particulate filter (DPF) cell (NGK Insulators, ltd.). Diesel particulate filter is a device equipped on exhaust system for purifying exhaust gas of small particles emitted from the engines. In general, DPF consists of lots of long square channels having small cross sectional area, e.g. 1.3 x 1.3 mm2, on each channel and porous wall which links each channel. We measured velocity distribution of pressurized methane gas flowing inside the channels using velocity encoding methods with spatial resolution of 250 ␮m and revealed that wall-flow passing through the porous wall is relatively uniform over the channel flow direction. Furthermore, we conducted experiments in which small carbon particles was seeded in supplied gas to simulate deposition process in the filters. We carried out pressurized gas MRI under 10.0 MPa with spatial resolution of 100 ␮m to probe particle deposition in the filter. We successfully visualized that particles plugged the flow channels and found that particles tend to deposit on the outlet side of the channels because of its inertia. We also found that particle deposition causes reduction of permeability of the outlet side of filter locally, resulting in increase of flow passing through the inlet side of porous wall in the DPF cell.

References [1] Koptyug, IV, Altobelli, SA, Fukushima, E, Matveev, AV and Sagdeev, RZ. Journal of Magnetic Resonance 147, 36 – 42 (2000). [2] Tsushima, S, Okamoto, I, Suekane, T and Hirai, S. Magnetic Resonance Imaging, Vol.19, 586 –587 (2001).

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Approaches to the characterisation of disordered porous systems by PGSE-NMR observation of diffusion and flow Joachim E. Tillich, Manfred Holz Institut fu¨r Physikalische Chemie, Universita¨t Karlsruhe, D-76128 Karlsruhe, Germany PFG-NMR is a suitable method for diffusion measurements but it is also capable to study flow phenomena in porous media [1,2]. In our work we characterize properties of porous media using the NMR flow-diffraction method [1]. Packs were made of glass spheres with diameters of 250 –300 ␮m and of the xerogel sephadex LH20. A precise flow of distilled water was achieved with a HPLC piston pump. The amplitude and the phase angle of the echo-signal were measured as a function of the wave-vector q ⫽ ␥␦G/2␲ in an alternating pulsed magnetic field-gradient STE experiment [3]. The observed signal attenuation shows a normal behaviour as found in previous studies [4,5] whereas the phase angle as function of the wavevector q shows characteristic changes in the slope: At q-values where a minimum of the signal intensity in the diffraction experiment occurs, we observe a phase jump [6]. This behaviour could be understood for laminar flow and plug-flow in a cylindrical pipe. In porous media the phase jump is smoother and rather a change of sign in the slope of the phase angle, and it depends only on the structure of the packs and not on the flow velocity. In this work we show an attempt to understand the behaviour of the phase angle in porous media and to correlate the slope of the phase angle with the structure of the porous system. We also observed that in the polydisperse sephadex gel the phase jump is visible although no coher-ence peak in the diffraction pattern appears, so the observation of the phase angle seems to be more appropriate for the investigation of polydisperse systems than the normal diffraction experiment. Further we could show in the present work that in porous media the flow velocities are observation time-dependent. A pressure driven flow of water molecules was observed in a pack of glass beads, resulting in a time-dependent behaviour similar to that of anomalous diffusion. In that way we were able to determine e.g. correlation lengths of sphere packs. In contrast to anomalous diffusion measurements [7] the observation timedependent flow measurements have the advantage that we can adjust the range of displacements to explore larger structural scales. Finally, we present a first example of the combination of dynamic imaging (DI) and MRI, where in heterogeneous porous systems (with an heterogeneity length scale in the mm to cm range) local characteristic quantities can be derived, as local surface-to-pore volume ratios (S/Vp) and local tortuosities. We show that by the combination of DI and MRI even in sample regions where the typical length scales are smaller than the resolution of MRI, structural information can be obtained.

References [1] Callaghan PT, Codd SL, Seymour JD. Concepts Magn Reson 1999; 11:181 [2] Price WS. Concepts Magn Reson 1997;9:299 [3] Cotts RM, Hoch MJR, Sun T, Markert JT. J Magn Reson 1989;83:252 [4] Seymour JD, Callaghan PT. AIChE J 1997;43:2096 [5] De Panfilis C, Packer KJ. Eur Phys J AP 1999;8:77 [6] Tillich JE, Heil SR, Holz M. Magn Reson Imag 2001;19:586 [7] Frosch GP, Tillich JE, Haselmeier R, Holz M, Althaus E. Geothermics 2000;29:671

Study of flow velocity profile and distribution in packed beds X. -H. Ren, S. Stapf, B. Blu¨mich Institut fu¨r Technische Chemie und Makromolekulare Chemie, RWTH Aachen, Worringerweg 1, D-52056 Aachen, Germany Detailed knowledge of the fluid flow profile is essential for proper design of fixed bed processes. Due to the non-uniform radial distribution of voidage, permeability, and interstitial velocity in a critical region close to

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the wall, the ratio of tube diameter (dt) and particle diameter (dp) may influence transport properties in fixed bed catalytic reactors. Despite the multitude of publications, systematic investigations for low tube-to-particle ratio dt/dayp are missing, especially for non-spherical particles. In this work, magnetic resonance imaging (MRI) and pulsed gradient stimulated echo (PGSTE) nuclear magnetic resonance experiments are used to probe the velocity profile and velocity distribution in packed beds at low tube-to-particle diameter ratio. The influence of flow rate Fv (1.0 mL/s –13 ml/s), the dimensionless tube diameter dt/dp (1.3–30), as well as the shapes of the catalyst pellets have been examined. Stagnant and moving fluid fractions can be distinguished in the experimental data from the averaged flow propagator. While the molecules in the streaming fluid migrate over steadily increasing distance with increasing observation time and flow rate, the stagnant fluid fraction decreases continuously. Apart from the dependence of the profile of the averaged displacement propagator on the dimensionless tube diameter and therefore the Pe´clet number, it was found to be considerably influenced by the shape and the type of the porous catalysts. The fluid confined in the pores of the regular cylindrical or the spherical catalyst pellets contributes more significantly to the stagnant phase, and the spread of the velocity distribution is much broader and more heterogeneous, leading to a smaller fraction of moving fluid. This was also proved by the spatial velocity distribution with NMR imaging. Significant heterogeneity was observed in velocity distribution. In particular, all measured radial flow profiles are characterized by a higher velocity in the vicinity of the tube wall. The peak velocities are located at distances of dp/4, dp, and 2dp from the wall, where the bed has also peak voidages. Moreover, from the average displacement flow propagator derived by the PGSTE experiments, the dispersion coefficients are determined over a range of observation times over which the flow develops. The dispersion properties obtained from these velocity profiles have been shown to correlate well with the results of non spatially resolved traditional chemical engineering methods, but provide a much more detailed description of the spatial dependence of the flow process. NMR diffusometry and cryoporometry on a naphtha reforming catalyst X.-H. Ren, S. Stapf, H. Ku¨hn, D. E. Demco, B. Blu¨mich Institut fu¨r Technische Chemie und Makromolekulare Chemie, RWTH Aachen, Worringerweg 1, D-52056 Aachen, Germany In catalytic hydrocarbon conversion processes, the reversible deactivation of the catalysts has been mainly associated with the carbonaceous residues (coke) formed on the catalyst surface, which shrinks the pore space and inhibits the molecular transport. Therefore the interest in these catalysts lies not only in their high catalytic activity and selectivity, but also in the possibility of regenerating them several times so that their “lifetime” is compatible with the cost of their production. Compared to the deactivation process, the understanding of several aspects of the fundamental mechanisms of the regeneration process remains poor or inconsistent which has hindered the simulation and optimization for both procedures. In this work, a series of naphtha reforming catalysts from different stages of the deactivation (coking) and the regeneration (decoking) processes were investigated by NMR diffusometry and NMR cryoporometry. The measurement of the self-diffusion coefficient is performed using a PGSTE sequence and the tortuosity was evaluated from the ratio of the diffusion coefficient of the confined and bulk liquids. The tortuosity was found to be correlated with the degree of coking, albeit a complex dependence, providing insight into the distribution of coke inside the pore space. Longitudinal (T1) and transverse (T2) NMR relaxation times of adsorbed liquid n-heptane provide information on changes of the pore morphology which can be corroborated by the tortuosity measurements. Based on the technique of freezing a liquid in the pores and measuring the melting temperature by nuclear magnetic resonance, the pore size distribution of the catalyst has been measured and is compared to Xe

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spectroscopy and nitrogen adsorption (BET) measurements which show an equivalent behavior. Furthermore, the diffusion and relaxation properties of freezing cyclohexane at different temperatures have also been investigated and analyzed. It was shown that the total elimination of carbonaceous residues by decoking induces changes in the pore size distribution and therefore the tortuosity. All the experimental results indicate that a full recovery of the activity of the clean catalyst is not achieved by the regeneration process, and that the quality of regeneration depends on the coke content reached during the deactivation/regeneration cycle. Diffusion- and T2- distributions of water and oil simultaneously present in a porous rock Henrik W. Anthonsen,1 Geir H. Sørland,1 John G. Seland,1 Jostein Krane,1 Frank Antonsen,2 Håkon Rueslåtten2 1Department of Chemistry, Norwegian University of Science and Technology, N-7491 Trondheim, Norway 2Statoil Research Centre, N-7005 Trondheim, Norway In the oil industry one is frequently faced with the problem of making quantitative measurements of the various fluid phases confined in the reservoir rocks. It is often difficult to apply traditional NMR measurement techniques to cope with this problem. We present a method, which combine a pulsed field gradient technique (PFG-NMR) for the recording of diffusion-related attenuation and a CPMG measurement of the transverse relaxation behaviour (T2). Using this method we obtain diffusion-weighted recordings of the T2-attenuation in a multi-component system consisting of oil and water saturated porous sandstone. Combined with a novel approach of processing the experimental data it is possible to obtain separated T2-contributions for oil and water in a porous system. The method is based on the fact that water normally has significantly higher self-diffusion than oil (e.g. crude oil). For this reason, the combined PFG-CPMG sequence is weighting the T2-attenuation to such a degree that the water gradually will contribute less and less to the T2-attenuation when applying an increased gradient strength in the PFG-CPMG sequence. When the gradient strength is sufficiently high, the signal contribution from water becomes negligible, and the T2-attenuation is originating from the oil phase only. When the mobility of all components within the oil phase is significantly lower than the mobility of water, it is possible to subtract a rescaled version of the T2-attenuation from oil only, in a combined PFG-CPMG

sequence with the pulsed field gradients set to zero. The resulting T2attenuation will then originate from the water phase, only. Following such a procedure for separation of multi-component attenuation, we have been able to measure the T2-contributions from oil and water separately in oil and water saturated porous sandstone. The NMR experiments are carried out on a 0.047 Tesla permanent magnet (Big2) from Resonance Instruments with available gradient strengths up to 150 Gauss/cm.

Quantitative studies of oil and water in rock cores Geir Humborstad Sørland, Per Magnus Larsen, Alf Petter Rudi Anvendt Teknologi AS, Hagebyv.32 N-9404 Harstad, Norway Hogskolen i Tromso, N-9293 Tromso, Norway The use of low field NMR to investigate oil and water in rock is usually limited to the study of a sum of the oil and water NMR-signal using conventional techniques as CPMG, Inversion Recovery, or PFG experiments. A separate measure for the amount of water and the amount of oil has been difficult to obtain as long as the T1- and T2-distributions have been overlapping. When using the PFG technique it is possible to resolve the oil and the water signal as oil usually exhibit a significantly lower self-diffusion. However, NMR signal is lost during the PFG sequence due to relaxation processes, which makes it difficult to achieve proper quantification using the ordinary PFG sequences. With this in mind Anvendt Teknologi A/S has developed a method for quantification of oil and water in rock cores. As for the PFG techniques, the method resolves the water and the oil due to their different self-diffusion coefficients. However, the method also takes into account the initial (or total) proton NMR signal. Then no NMR signal is lost due to relaxation processes (Fig. 1).

Determination of fat and moisture content in food stuff P. M. Larsen, F. Lundby, A. P. Rudi, G. H. Sorland Anvendt Teknologi AS, Hagebyv. 32 N9404, Harstad, Norway MATFORSK, Osloveien 1, N-1430 Ås, Norway Hogskolen i Tromso, N-9293 Tromso, Norway The use of low field NMR to determine fat and water in foodstuff, as meat-, fish-, and dairy products, has previously been of limited interest. The reason for this is the lack of an instrument that would be capable of resolving the fat signal from the water signal and at the same time being

Fig. 1. Visualisation of the separation of oil and water signal from a porous rock. The broad peak represents the unresolved T2-distribution while the narrow peaks represents the oil signal (right peak) and the water signal (left peak). The distribution is resolved due to the difference in self-diffusion between oil and water.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

433

Fig. 1. Comparison of the NMR fresh method with chemical extraction and with NMR dried method (where the moisture has been dried out). 42 samples of minced beef meat with fat content varying from 1% to 15% were studied. accompanied with a method that is fast, accurate, easy to handle and simple to calibrate. We believe to have developed such a method and it is implemented on a Resonance Instruments Maran23, where a sample weight up to 10 grams can be analysed using an application tool following the instrument. It takes less than 1 min to measure the total fat content, while it takes less than 2 min to measure both fat and moisture content. Currently the method can measure the fat content in foodstuff, and moisture content in non-sugar containing foodstuff. (Fig. 1).

共2⌬兲 ⫽

1 p

冕

⬁ F

共 ␻ 兲 2b共 ␻ 兲 d ␻ , where F共 ␻ 兲 2

0

⫽ F a共 ␻ 兲 2 ⫹ 2F a共 ␻ 兲 F s共 ␻ 兲 ⫹ F s共 ␻ 兲 2. The dominant susceptibility effect comes from the mixed term, which can be neglected if a proper modulation shifts the spectrum of susceptibility Fs(␻) outside the range of the applied gradient spectrum Fa(␻). The method is demonstrated by diffusion weighted 1D MR micro images of water contained in a 2.8 mm wide notch milled in a piece of plexiglass acquired on a 2.35 T MR imaging system (Fig. 1). The first MR image was obtained by the PGSE sequence in which the second gradient pulse was prolonged to acquire the signal for 1D MRI, while the second MR image was obtained by the modified PGSE with a CPG RF pulse train to reduce susceptibility effects. The first MR image has less attenuated signal in the center of the profile than expected because of internal magnetic fields that reduced the effect of the external magnetic field gradient. The second MR image well agrees with the theoretical model [3]. The signal in the center of the profile is attenuated as expected for free self-diffusion, while the edges are enhanced due to restraint of molecular motion near proximity of impermeable walls.

The reduction of the susceptibility effect in diffusion measurements of porous media using a modified PGSE sequence: demonstration by MR micro-imaging Andrej Duh, Ales˘ Mohoric˘, Igor Sers˘a, Janez Stepis˘nik Institute of Mathematics and Physics, University of Maribor, Faculty of Electrical Engineering and Computer Science, Smetanova 17, 2000 Maribor, Slovenia Physics Department, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia Contrasts in NMR micrographs tend to be diffusion weighted due to the motional restriction of diffusing particles by impermeable walls. In a strong magnetic field, the resolution is reduced also due to the susceptibility difference between the solid material and the fluid, which causes local distortions of the magnetic field. The CPG RF pulse train interspersed with a pulsed field gradient sequence can be used to remove the effect of the susceptibly difference [1]. The applied CPG sequence modulates the effect of a background gradient while keeping the dephasing by applied gradients unchanged. The spectral analysis [2] gives the spin echo attenuation as

References [1] Williams WD, Seymour EFW, Cotts RM. J Mag Res 1978;31:271 [2] Stepisˇnik J. Physica B 1981;104:350 – 64. Callaghan PT, Stepisˇnik J. J Magn Reson 1995;A117:118 –22. [3] Stepisˇnik J, Duh A, Mohoric˘ A, Sers˘a I. J Mag Res 1999;137:154 – 60 [4] Duh A., Mohoric˘ A., Stepisˇnik J., Sers˘a I. J Mag Res (to be published).

Fig. 1.

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Water front migration in porous media monitored by dynamical 1D MR imaging Igor Sersˇa, Tadej Kokalj Josˇef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia

A Fast Field Cycling NMR Study of Soil C.L. Bray, D.Y. Lee, J.P. Hornak Rochester Institute of Technology, Rochester, NY 14623 USA V. Satheesh, S. Sykora, G. Ferrante Stelar s.r.l., via Enrico Fermi 4, 27035 Mede (PV), ITALY

Water in pores of many materials is often unwanted since it may reduce their durability and lifetime. From that perspective it is important to understand how water migrates into these materials. Dynamical high resolution MR imaging is a very convenient tool for such investigations as it is accurate, fast and noninvasive. Here we present a simple dynamical 1D MRI study of water migration into a piece of chalk. A small piece of chalk with a diameter 2 mm and 20 mm long was inserted into a micro-imaging probe. The spin-echo sequence with an echo time 2 ms and a recovery time 500 ms was used to dynamically acquire a set of 200 1D images of a water concentration profile along the long axis of the sample. Each profile was acquired in one second as an average of two acquisitions. Approximately 30 s after the beginning of the imaging a small water drop was dropped to one side of the sample. The drop was absorbed immediately into a chalk due to large capillary forces so that pores up to the depth of 3 mm were completely saturated with water. This was followed by water migration from saturated pores to those with lower water concentration. This process may be well seen in a Fig. 1a) on a set of 1D profiles where the average depth of pores filled with water increases with a square root of time. The same process was also computer simulated (Fig. b). The criterion used in the simulation of water migration was pore saturation. A probability for a water molecule to migrate into a pore next to it was inversely proportional to a difference between a water concentration in a saturated pore and the water concentration in that pore. Water migration may be mathematically well modeled by a model that combines the water imbibition (square root of time law for an average water front depth) with diffusion [1]. C共 x,t兲 ⫽

冉

C0 1 ⫺ erf 2

冉

x⫺ 冑D it 2 冑Dt

冊冊

.

In 1962, Varian proposed the use of NMR to prospect for water in deep gravel layers [1]. This technique has since been improved for use at depths down to 100m [2]. We are interested in applying a similar technique to extract spatial information of the water content in soil nearer the surface of the earth. A first step in determining the feasibility of such a technique is to study the NMR signal from the water in soil. This work concentrates on the contribution to the NMR signal from the spin-lattice relaxation rate, R1. R1 studies of soils and synthetic soils at a single high frequency have been performed [3,4]. This study focuses on R1 values as a function of magnetic field strength Bo, where Bo is less than 280 mT. Surface soil samples were collected from five locations in the USA. The particle size distribution in the samples was determined by optical microscopy. Samples were hydrated with HPLC water to the point of saturation for at least six months. A Spinmaster-FFC 2000 (Stelar s.r.l., Mede, ITALY) fast field cycling NMR relaxometer was used to obtain 16-point relaxation curves at 20 magnetic field values (Bo) between 0.2 and 280 mT for the five soil samples. Relaxation curves were fit with Both monoexponential (ME) and biexponential (BE) functions with an offset. Some of the relaxation curves clearly displayed BE behavior, while others displayed only ME behavior. The BE behavior is perhaps indicative of a structured water component, experiencing the influence of the surface of the soil particles, and a free water component, influenced to a lesser extent by the soil particles. The calculated R1 values displayed a decreasing trend with increasing Bo, and an approximately linear relationship as a function of log(Bo) over the entire Bo range. The decreasing R1 with increasing Bo indicates that when designing a field based MRI system, it will be preferable to use larger Bo values for more favorable relaxation rates. Assuming the spin-spin relaxation rate, R2, will be greater than R1, many of the soils will have a structured water signal component that will be unobservable with a moderate cost detection system associated with a portable field based MRI system. Relaxograms and correlations with soil particle distribution will be presented.

(1)

Two free parameters Di and D were extracted from the best fit between the model (Eq. 1) and the experimental data (Fig. a). The best fit yielded D i ⫽1.04䡠10 ⫺7 m2/s and D ⫽ 1.40䡠10 ⫺8 m2/s. The presented method can be also applied for study of many other porous maetrials where water migration is in general considerably slower. Slower migration would allow longer signal acquistion for a profile and hance enable study of materials with low porosity that also have low water content.

References 1. RH Varian. Ground Liquid Prospecting Method and Apparatus, US Patent 3,019,383, (1962). 2. DV Trushkin, S Shushakov, AV Legchenko. Geophysical Proceeding 42:855– 862 (1994). 3. ZR Hinedi, AC Chang, et al. Water Resour. Res., 33:2697–2704 (1997). 4. ZR Hinedi, ZJ Kabala, et al. Water Resour. Res., 29:3861–3866 (1993).

References [1] Bear J. Dynamics of Fluids in Porous Media, Elsevier, New York, 1972, 579 – 663.

Fig. 1.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

1H NMR And solvent spin relaxation studies of thermosensitive copolymers at colloidal interfaces M. Rusu, A. Larsson, M. Scho¨nhoff, S. Wohlrab, D. Kuckling Max Planck Institute of Colloids and Interfaces, 14424 Potsdam/Golm, Germany Institute for Surface Chemistry, P. O. Box 5607, SE- 11486 Stockholm, Sweden TU Dresden, Institute of Macromolecular Chemistry, 01062 Dresden, Germany The dynamics of polymers at interfaces can deviate substantially from the dynamics in bulk. Adsorption layers and multilayers can be studied by NMR methods, provided that they are adsorbed to colloidal particles with a sufficiently large surface area. The incorporation of functionalities, such as temperature dependence, into multilayers is a promising goal. Thermoreversible polymers in solution undergo a transition from a water-soluble to an insoluble state with increasing temperature. This phase transition is called “coil-to-globule” transition. Here, we investigate such polymers concerning their phase transition properties at solid interfaces. The thermoreversible polymer Poly-N-isopropylacrylamide (PNIPAM) and different charged PNIPAM co-polymers are studied, since charged groups are required for electrostatic layer formation. 1H liquid state NMR spectra and 1H solid echo relaxation experiments monitor the signal of mobile spins and their transition to immobile segments. For the charged copolymer, the transition is broadened, and mobile segments remain even above the transition temperature. This is attributed to a comparatively mobile arrangement of the copolymer layer: Due to the electrostatic repulsion from the surface and between polymer segments, the copolymer layer is probably confined in a configuration extending further from the interface [1,2]. According to these results, improved polymer architectures are synthesized, consisting of a thermosensitive backbone and charged side chains 3. These co-polymers provide properties of polyelectrolytes and of classical thermosensitive polymers, which are promising for the fabrication of thermoreversible polyelectrolyte multilayers. 1H NMR studies of the coil-to-globule transition of both co-polymers in solution show that the lower critical solution temperature (LCST) is increased as compared to the side chain grafting density. This is attributed to the repulsive interaction between charged side chains, which hinders the rearrangement necessary for collapse. Multilayer formation using self-assembly processes has been achieved with these copolymers. Solvent spin relaxation rates R2 monitor the hydration water in multilayers, and can thus be employed to investigate phase transitions in multilayers.

References [1] Larsson A, Kuckling D, Scho¨nhoff M. Coll Surf A 2001;190(1–2):185. [2] Scho¨nhoff M., Larsson A., Welzel P.B., Kuckling D. J. Phys Chem B, subm. [3] Wohlrab S, Kuckling D. J. Polym Sci A 2001;39:3797. Relaxation of 22Na and 35Ci in porous building materials L. A. Rijniers, J. Petkovic´, L. Pel, P. C. M. M. Magusin, K. Kopinga Eindhoven University of Technology, Department of Physics, P. O. Box 513, 5600 MB Eindhoven, The Netherlands Eindhoven University of Technology, Department of Chemical Engineering and Chemistry, P. O. Box 513, 5600 MB Eindhoven, The Netherlands Dissolved salts in porous building materials can crystallize during drying, which may occur at the surface, causing defacing, or just below the surface, where it may cause structural damages. In addition, salts promote corrosion of the reinforcements in concrete. In order to understand these deterioration processes and increase the durability of the materials, the mechanisms that govern the moisture and salt transport in porous building materials have to be known in detail.

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In studying ion transport and crystallization effects, knowledge in which part of the pore system the relevant ions are present, e.g., in large pores or small pores, might prove to be essential. For this purpose the ion distribution within the pore system has to be measured. Up to now, an analysis of the distribution of the relaxation times of the hydrogen nuclei is used to determine the pore water distribution, i.e., the distribution of the water over the various pore sizes. In the interpretation of these data the fast-diffusion limit is assumed. We have investigated whether a similar approach can be used for dissolved ions. To this end we measured the transverse relaxation of Na in a bulk NaCl solution as well as in a series of materials (Nucleosil) with well defined pore sizes. Measurements were performed for NaCl concentrations ranging between 0.1M and 5M using CPMG pulse sequences with an echo spacing of about 2 ms. Special attention was given to the possible effects of the quadrupole moment of 23Na (I⫽ 3/2) on the NMR signal and relaxation. In principle, Na ions close to the pore walls may interact with local electric field gradients, causing line splitting or broadening. In our experiments no loss of Na signal was found in the porous materials compared to the bulk, i.e., the ratio of the H and Na NMR signal intensities remained constant. This demonstrates that ultra fast relaxation processes –if any –are negligible and that the Na line broadening is smaller than our experimental bandwidth (12 kHz). This was confirmed by high resolution MAS experiments. The transverse relaxation of Na in these porous materials could be modeled similar to that of H, i.e., in terms of pore wall relaxation mediated by diffusion. We also measured the Na spin-echo decay in some porous building materials. The resulting relaxation time distribution was combined with comparable NMR data on hydrogen to deduce the Na distribution over the pores. Preliminary studies on 35Cl (I ⫽ 3/2) reveal a behavior similar to that of Na. Also in these experiments the relaxivity at the pore wall is rather fast, which is attributed to quadrupolar effects.

A magnetic resonance study of the water-distribution and -movement during microwave vacuum drying of food Marc Regier, Helmar Schubert Institute of Food Process Engineering, University of Karlsruhe, Kaiserstr. 12, D-76131 Karlsruhe, Germany Microwave vacuum drying has many advantages over conventional drying processes: Extraordinary fast drying rates due to microwave energy input are combined with low thermal stress and the prevention of undesired chemical reactions (Maillard-reaction, oxidation) due to vacuum conditions. Besides high volume retention, nearly no aroma loss in case of oil soluble flavours and a uniform drying can be obtained. Nevertheless, a complete model, covering electromagnetism and massand heat-transport, is missing since still deficits exist in the knowledge of the water distribution and movement during drying. In this work, magnetic resonance imaging (MRI) and pulsed field gradient nuclear magnetic resonance (PFG-NMR) is used to study the water distribution and the water self diffusion coefficients in apple tissue during microwave vacuum drying. For this task a lab-scale microwave vacuum dryer with continuous power control was developed: Beside a continuous fibre optic sampletemperature indication, a balance yield online the integral drying rate. The dryer could be set up directly next to the NMR-magnet, so that short transport times between the drying and the MR imaging resulting in negligible sample changing became possible. By a fast imaging sequence (RARE) the three dimensional water distribution within the apple samples was measurable. The total water amount could be calculated by integrating the proton spin density, and quantitatively fit the value, otained by drying and weighing. The influences of different microwave drying programs on the drying homogeneity could be analyzed in figures of the radial, axial and azimuthal water distribution. The results show, that programs with long microwave power breaks yield the most uniform water distribution. The self diffusion coefficients, measured by PFG-NMR, exhibit, that

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Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

the diffusion occurs predominantly in the fluid phase. They decrease with proceeding drying due to the increasing sugar concentration and the consecutive higher viscosity. The observation time dependency of the self diffusion coefficients yields the tortuosity and the surface-to-volume-ratio, that may serve as parameters in a mass transport model. The extracted data fit well with corresponding microscopy studies of the pore and cell structure and with the macroscopic shrinking of the samples.

Acknowledgements The authors thank the Deutsche Forschungsgemeinschaft (DFG) for financial support in project FOR338. 2

H NMR investigations of internal dynamics and structures of surfactants adsorbed in porous silica materials Ying Qiao, Monika Scho¨nhoff Max-Planck-Institute of Colloids and Interfaces, 14424 Potsdam/Golm, Germany

Selectively deuterated nonionic surfactant (C12E5) adsorbed at the solid/ liquid interface is investigated using 2H solid state NMR. The substrates are porous silicas of different pore sizes (narrow pores: 1.9 – 4 nm, wide pores: 5–24 nm) and shapes (CPG glass/worm-like shape, SBA-15/2-D hexagonal tubes, SE silicas/distorted hexagonal tubes, tubular/slit-like micro-pores etc.). All surface aggregate spectra exhibit an isotropically averaged Lorentzian line shape, with relaxation rates R2 of several kHz, which suggests a slow motion correlation time of several ms. Assuming 2-dimensional diffusion to be the relevant mechanism, the diffusion length for achieving isotropic averaging can be estimated, which indicates the details of inner pore structures. The structural arrangement of the adsorbed surfactant is represented in terms of relative order parameter profiles Srell of the C-2H bond. The order of magnitude of Srel is 1–1.1 in the wide pores. In comparison to a previous investigation of different aggregate shapes of the same surfactant [1], this suggests that the structures of the surface aggregates formed in the wide pores are bilayers. An interesting discovery is that the simple, increasing relationship between Srel and the distance of the 2H label position from the head group found previously [1] remains true only for the wide pores; for narrow pores (⬃ C12E5 chain length), the ␤ position has more mobility than both a and g positions. This suggests the existence of a phase transition induced by the confined geometry and is the first observation of such a kind.

Acknowledgments We thank Prof. G. H. Findenegg and Dr. B. H. Han for providing the porous silicas, Prof. H. Mo¨hwald and Prof. M. Antonietti for valuable discussions.

References [1] Scho¨nhoff M, So¨derman O, Li ZX, Thomas RK. Langmuir 2000;168: 3971.

STRAFI-NMR of partially drained porous materials A. R. Preston, N. R. A. Bird, W. R. Whalley, E. W. Randall Dept. of Chemistry, Queen Mary, University of London, Mile End Road, London, E1 4NS, United Kingdom Soil Science Group, Silsoe Research Institute, Wrest Park, Silsoe, Bedford, MK45 4HS,United Kingdom Partially saturated materials are very important in agriculture as this relies on a soil matrix with pores containing both air and water. Pore size

distributions in soil are often obtained from water retention curves; the water content of a series of soil samples is determined gravimetrically after draining each to a different matric potential. These curves can be converted to pore size distributions using a range of increasingly complex models; for example Pore-Cor [1]. We wish to show where in the material the water is located when it is partially drained. Low resolution NMR is a well-known technique for studying saturated porous materials. We have been using STRAy FIeld STRAFI-NMR to investigate soil samples [2]; the strong continuously applied gradient of the fringe field (12.1 Tm⫺1 in our case) of a superconducting magnet dominates the internal field gradients caused by local susceptibility variations. This allows us to obtain information from a narrow (⬃0.1 mm thick), well-defined slice of the material. The matric potential and hence the water content of the sample can be varied in situ. Earlier observations on saturated ceramic blocks showed the expected variation of longitudinal relaxation time with pore-size and also that the data could be analysed to show the predicted spatial behaviour from a two component phantom [3]. A series of soil samples with increasing silt content were examined both fully wet and at a range of matric potentials. Recovery curves obtained using a progressive saturation technique were analysed as a distribution of exponentials using CONTIN [4]. The results were encouraging: the distributions obtained from fully water-saturated soils correlated well with those deduced from water retention curves. Distributions obtained for partially drained soils were consistent with the hypotheses that not all pores of a given diameter will drain at a fixed matric potential but that some large ones will remain full if isolated by narrow throats. New very short decay times will appear corresponding to water trapped in crevices of partially drained pores, or retained as pendular structures between grains. The results of further experiments on model systems such as sands and glass microspheres to test the validity of these conclusions will be presented. Also, the techniques of progressive saturation and inversion recovery [5] in the STRAFI mode will be compared. Simulations of these methods using the GAMMA platform [6] to check for the validity of CONTIN analysis will be discussed as well as the influence of SNR (signal to noise ratio) on the fits.

References [1] Peat DMS, Matthews GP, Worsfold PJ, Jarvis SC. Eur J Soil Sci 2000;51:65–79. [2] Preston AR, Bird NRA, Kinchesh P, Randall EW, Whalley WR. Magn Reson Imaging 2001;19:561–3. [3] Kinchesh P, Samoilenko AA, Preston AR, Randall EW. J Environ Qual 2001;31:494 –9. [4] Provencher SW. Comput Phys Commun 1982;27:229 – 42. [5] Hurlimann MD. J Magn Reson 2001;148:367–78. [6] Smith SA, Levante TO, Meier BH, Ernst RR. J Magn Reson A 1994;106:75–105.

NMR studies of naphthalene in porous SOL-GEL silicas Jonathan Mitchell, John H. Strange School of Physical Sciences, University of Kent at Canterbury, Canterbury, Kent, United Kingdom, CT2 7NR The method of NMR cryoporometry [1] has been well documented for the study of pore size distributions. This method utilises the depression in melting point of a confined material [2]. It has previously been conducted using probe materials that have sub ambient bulk melting points, for example water and cyclohexane. This method has now been extended to probe materials with super ambient bulk melting points, for example naphthalene confined in well-characterised sol-gel silicas. Naphthalene has a melting point depression of 1810KÅ, similar to that of cyclohexane, making it sensitive up to pore diameters of about one micron. Due to the large molecular size of naphthalene the useful lower pore limit is increased to about 40Å. High temperature cryoporometry has the advantage over

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 sub-ambient measurements of the simplified temperature control without the use of cryogens. Motional studies of confined naphthalene have also been conducted using NMR relaxation time measurements. Bulk naphthalene has been previously modelled as having three rotational axes [3]. This was tested and clear evidence for an in plane rotation observed whilst diffusion was less than that of a typical plastic crystal [4]. Molecular mobility has been observed to be significantly enhanced when the naphthalene is confined in pores. T1 of naphthalene in the pores is several orders of magnitude lower than the bulk at room temperature. Similarly T2 at the same temperature is increased from about 10␮s to 100␮s. T1 and T2 change over a temperature range below the pore-melting region suggesting greatly increased rotational motion and a more mobile surface layer. T1 and T2 values depend on pore diameter in both solid and liquid phases. The apparent activation energies calculated from T1 and T2 are 62 ⫾ 4 kJ mol⫺1 and 15 ⫾ 2 kJ mol⫺1 respectively.

References [1] [2] [3] [4]

Strange JH. Nondestr Test Eval 1994;11:261. Jackson CL, McKenna GB. J Chem Phys 1990;9312:9002. Andrew ER. Chem Phys 1950;185:607. McGuigan S, Strange JH. Molecular Physics 1983;492:275.

Study of polymeric ion exchangers and their selectivity to organic ions by using 31P NMR spectroscopy A. Marton, H. Sakashita, Y. Miura, E. Hiramatsu, Y. Miyazaki Atmospheric Chemistry Research Group of the Hungarian Academy of Sciences, University of Veszpre´m, H-8201 Veszpre´m, Hungary Center of Advanced Instrumental Analysis, Kyushu University, Kasugakohen, Kasuga, Fukuoka 816-8580, Japan Department of Chemistry, Fukuoka University of Education, Akama, Munakata, Fukuoka 811-4192, Japan Ion exchange distribution of phosphonic and phenylphosphoric acids have been studied on various types of chloride form strong base ion exchange polymers as a function of pH at 25°C, at 0.1 M ionic strength. The selected polymers include styrene - divinylbenzene and polysaccharide based matrices with various type of cross-linkings and pore sizes. In our studies phosphorous acid has been selected as a particular model compound because of the similarity of its protonation sites to the proton binding groups of the biological energy transfer molecules. The ion exchange reactions of these species can be considered as a simple model of the distribution between the cell wall and its environment. Equilibrium measurements were supplemented by the study of the pH dependence of the 31P NMR spectra of the polymer phase phosphorous containing species. Equations were derived to describe the pH dependence of the overall distribution coefficient and the 31P NMR chemical shift of the resin phase solute species. Experimental data were evaluated by using these model equations and the values of the individual distribution coefficients, ion exchange selectivity coefficients and the individual resin phase 31P chemical shifts of the mono and divalent ions have been calculated. The derived model equations made also possible the calculation of the pH inside of the porous cross-linked ionic polymer phases both from the equilibrium data and from 31P NMR measurements. Comparison of the distribution data of the individual species corroborated the significance of the role of hydrophobic interaction in the selectivity of organic ion exchange processes. The linear relationship observed between the calculated selectivity coefficients and the polymer phase 31P NMR chemical shifts of the species proves that interactions responsible for selectivity (thermodynamic parameter) and chemical shifts (spectroscopic data) are strongly correlated in the studied systems.

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Xe absorption and 1H NMR relaxation in investigation of crosslinked composite polymers A. Ferrando, G. Maddinelli, W. O. Parker EniChem Research Centre, Mantua, Italy EniTecnologie S.p.A., San Donato, Milan, Italy Composite polymers (e.g. HIPS and ABS) are widely industrially applied, especially for electronics and domestic appliances, due to their shock absorbing performance. However, their complex structures, constituted by rubber (mainly polybutadiene) dispersed in polystyrene matrix, is particularly difficult to characterise. One of the most critical structural parameters is cross-linking between the rubber chains. This chemical feature greatly affects chain motions and is determinant in controlling mechanical properties of the final product. NMR techniques are widely and efficiently applied to investigate such materials [1]. However, there is still a necessity for robust methods which can be efficiently applied in evaluating the degree of crosslinkage. 129Xe NMR spectroscopy could provide interesting information about structural properties of the dispersed phase. In recent years 129Xe NMR spectroscopy has been applied to polymers and polymer blends to probe morphology and domain sizes. Only two reports mention observing multiple 129Xe signals in cross-linked elastomers along with downfield shifting on increasing the cross-link density [2,3]. No systematic studies of downfield 129Xe shifting with increasing cross-link density have been reported. In our study we have investigated a set of HIPS (High Impact Polystyrene) samples with increased crosslink density of the rubber phase induced by thermal treatment and controlled by standard swelling measurements. 129Xe NMR spectra were collected at 83 MHz by absorbing Xe on the polymer inside a 10 mm tube under moderate pressure. We observed, as shown on Fig.1a, good correlation between downfield 129Xe shifting and the crosslinking degree (swelling index) of HIPS samples. Crosslinking variation on such samples was also investigated by transversal 1H relaxation times analysis at low magnetic fields (20 MHz). In this application previous studies on model samples [4] were extended to such complex materials. Also this approach allowed observation of the crosslink density variation in the samples examined. In fact, a shift forward low values of T2 in the longest fraction of the relaxation time distribution was observed. Both proton relaxation analysis and 129Xe NMR spectroscopy

Fig. 1. Graphs showing 129Xe chemical shift data plotted against curing time (a) and swelling index (b).

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were found to be simple and promising techniques for investigating crosslink densities of elastomeric materials.

References [1] Blumler P, Bluemich BNMR imaging of elastomersa review. Rubber Chem Tech 1997;70:468. [2] Menge H, Kuhn H, Blumich B, Blumler P, Schneider H. Macromol Mater Eng 2000;282:1– 4. [3] Kennedy GJ. Polym Bull (Berlin) 1999;23:605. [4] Borgia GC, Fantazzini P, Ferrando A, Maddinelli G. Characterisation of crosslinked elastomeric materials by 1H NMR relaxation time distributions. Magn Resone Imag 2001;19:405–9.

The influence of particle loading on hydrodynamics in fixed-bed reactors Matthew Lim, Lynn Gladden Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, United Kingdom Magnetic resonance (MR) imaging and flow visualisation techniques are finding increasing application in studying single- and multi-phase flows in chemical reactors. This paper addresses packings of porous particles –typically of dimension 1–3 mm –within a cylindrical column; in industrial applications such packing elements would be catalyst pellets. This study focuses on investigations of the hydrodynamics within such packings of particles, and in gaining an understanding of how the structure of the inter-particle space influences liquid flow. In this sense such experimental systems can be thought of as model porous media, with pore sizes on a length-scale that can be visualised directly using MR techniques. In optimising the operation of industrial reactors, the method of loading the catalyst particles in to the reactor is known to be important in determining reactor performance. However, the selection of loading procedures to be used remains, to a greater or lesser extent, empirical. We have used MR flow visualisation techniques to explore how simple modifications to the particle loading procedure influence the hydrodynamics within the bed and how this is related to differences in the structure and topology of the inter-particle space characterising the bed. For example, as seen in Fig. 1, comparison of so-called ’concave’ and ’convex’ loading protocols reveals a quite different location of high liquid velocity channels within the bed as a function of the protocol used.

References [1] Li M, Iida N, Yasuda K, Bando Y, Nakamura M. Effect of orientation of packing structure on liquid flow distribution in trickle beds. J Chem Eng J 2000;335:811– 4

Magnetic resonance imaging as a means to investigate local porosity and mass loading in fibrous filters Martin J. Lehmann, Joachim Tillich, Edme Hardy, Gerhard Kasper Institut fu¨r Mechanische Verfahrenstechnik und Mechanik (Gas-PartikelSysteme), Universita¨t Karlsruhe (TH), D –76128 Karlsruhe, Germany Fibrous filters are widely used as disposable media for air cleaning in automotive, HVAC and other applications. Numerous models have been developed to make predictions for pressure drop pressure drop and fractional efficiency of new filter media. In doing so, they usually ignore the fact that the internal pore structure of commercial media is not uniform, in part because non-destructive measurements are difficult, or they account for the substantial effects of non-uniformity by introducing adjustable parameters. We have developed a technique for measuring internal porosity distributions of low-density media by Magnetic Resonance Imaging (MRI). The method which we briefly describe is far from being a standard technique, but the results reported here are promising and accurate. CFD simulations of internal gas velocity distribution and overall pressure drop were performed on the basis of such MRI data for several types of real filter media. The numerical results are compared to Dp measurements. It is shown how the distribution of porosities and also the choice of spatial resolution impact the numerical results. Further more mass distribution of deposited particles in the filter medium is visualised by MRI. Issues of validating the MRI data are also discussed.

* Corresponding author. Tel.: ⫹49-721-608-6565; fax: ⫹49-721-6086563 [email protected] (M. Lehmann)

From random to correlated percolation networks: NMR velocity mapping in model objects Arnold Ku¨hnle, Markus Weber, Rainer Kimmich Universita¨t Ulm, Sektion Kernresonanzspektroskopie, 89069 Ulm, Germany Quasi two-dimensional objects have been fabricated based on correlated percolation clusters. The correlation was achieved analogous to the Ising model: The cluster growth probability is larger than the nucleation probability. The quotient of these probabilities is called growth-factor, and was

Fig. 1. MR visualisations of single-phase flow through packings of identical packing elements (black), loaded into a cylindrical column using different protocols. The work considers two protocols described by Li et al. (2000) which are known to give significant differences in trickle-bed operation. (a) “concave” loading, (b) “convex” loading. The superficial flow velocity is 1.3 mm/s. The ’convex’ loading protocol gives rise to substantial channel formation toward the wall region of the bed.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

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displacement and correlation functions of components of the segment tangent vector were the primary quantities to be evaluated. Two T1 dispersion regimes were distinguished for randomly coiled chains typical for the free Rouse chain dynamics and reptation. Depending on the effective tube diameter a crossover from Rouse to reptation behavior is clarified. Recently obtained results for the tubes formed by harmonic radial potential are in direct accord with our computer simulations [4]. Supported by Volkswagen-Stiftung, INTAS, CRDF REC-007, RFBR 02– 03-32921.

References Fig. 1. Typical correlated percolation cluster. The growth-factor is 100,000.

[1] Doi M, Edwards SF. The Theory of Polymer Dynamics, Clarendon Press, Oxford, 1986. [2] Fischer E, Kimmich R, Beginn U, Mo¨ller M, Fatkullin N. Phys Rev E 1999;59:4079. [3] Kimmich R, Seitter R.-O, Beginn U, Mo¨ller M, Fatkullin N. Chem Phys Lett 1999;307:147. [4] Denissov M, Kroutieva N, Fatkullin R, Kimmich J. Chem Phys 2002; 116:5217–35. Characterization of the mesoporous materials by 2H NMR L. Kimtys, D. W. Aksnes Department of Physics, Vilnius University, Vilnius 2734 Lithuania Department of Chemistry, University of Bergen, N-5007 Bergen, Norway

Fig. 2. Percolation threshold as a function of the growth-factor. varied between 3.2 and 100,000 (Fig. 1). The percolation-threshold depends on this factor and shows a minimum at a certain value (Fig. 2). The water-filled pore space of the model objects was investigated by NMR spin density and, after exerting a pressure gradient, by velocity mapping. The correlation length and the percolation probability were evaluated from the computer generated templates as well as from the corresponding NMR spin density maps. Based on velocity maps, the percolation backbones were determined. The experimental results favourably compare to FVM simulations.

Monte-Carlo simulations of polymer chain confined in tubes: segment diffusion and nuclear magnetic resonanse spin-lattice relaxation M. Kroutieva, A. Denissov, N. Fatkullin, R. Kimmich Kazan State University, Department of molecular physics, 420008, Kazan, Russia Dynamics of polymer chains confined in artificial cylindrical tubes is of stable interest, for numerous attempts have been undertaken to describe the entangled chains dynamics by the assumption of a fictitious tube representing the “matrix” surrounding a tagged chain [1]. Well-known frequency and molecular-mass dependences of NMR spin-lattice relaxation T1⬀M0␻0.75 for ␶e⫺1䊐 ␻䊐 ␻R⫺1 and time dependance of anomalous mean-squared displacement of Kuhn segment 具rជ2(t)典⬀M0t1/4 for ␶3䊐 t䊐 t䊐 ␶R were confirmed by experiments [2,3]. Monte-Carlo simulations for polymers modeled by Rouse chains confined in straight and randomly coiled cylindrical tubes with an infinitely deep square-well radial potential (“hard tube”) are carried out. To model the chain dynamics the modified Stockmayer chain model was applied. The tube diameter and chain length were varied. The mean-square segment

In this work we demonstrate the advance of the 2H NMR measurements in the study of the pore size distributions by employing cyclohexane-d12, water-d2, benzene-d6 confined within four controlled pore glasses and other porous materials of nominal diameter ranging from 4 to 30 nm. It is well known that liquids confined within small pores solidify at a temperature that varies inversely with the pore size. The melting point depression of the tiny crystals formed inside the pores ⌬T is given by the simplified Gibbs-Thompson equation ⌬T⫽kp/T where R is the pore radius and kp is a characteristic property of the liquid [1]. By measuring the fraction of melted liquid as a function of temperature, the pore size distribution can be determined if kp is known. The last decade, several workers have used 1H NMR to determine pore size distributions of porous materials employing water and some organic compounds as adsorbates, however, the kp value of adsorbates have never been calibrated using NMR [2– 4]. The liquid and solid components of the adsorbate can be distinguished, on the basis of the spin-spin relaxation time T2, by employing a spin-echo sequence with an inter-pulse spacing, ␶, the value of which depends on the origin of the adsorbate. However, if the solid adsorbate forms plastic crystals, with relatively narrow 1H NMR lines, rather long ␶ values might be needed to separate the two components. In the mesoporous range, the NMR technique gives overall pore size distributions comparable to those obtained by the conventional gas sorption method. In practise, however, pore sizes larger than approximately 50 nm in diameter will be difficult to determine accurately by NMR unless adsorbates undergoing larger melting point depressions than cyclohexane can be found. The obtained results are discussed with reference to the similar 1H NMR investigations.

References [1] Jackson CL, McKenna GB. J Chem Phys 1990;93:9002–11. [2] Webber JBW, Strange JH, Dore JC. Magn Reson Imaging 2001;19: 395–9. [3] Aksnes DW, Forland K, Kimtys L. Phys Chem Chem Phys 2001;3: 3203–7.

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[4] Aksnes DW, Forland K, Kimtys L, Sto¨cker M. Appl Magn Reson 2001;20:507–17.

Emulsion characterisation using magnetic resonance methods K. G. Hollingsworth, M. L. Johns Department of Chemical Engineering, University of Cambridge, Cambridge, United Kingdom The droplet size distributions of emulsions have been measured using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) for many years. This technique finds particular application with emulsions that are concentrated and/or opaque, since such emulsion systems are difficult to characterise by other methods (e.g. light scattering). Most studies employing PFG techniques assume a log-normal form when extracting the droplet size distribution from the experimental data, in order to simplify the complex inversion problem required. It is clearly desirable to retrieve a droplet size distribution from the experimental data without assuming such a functional form. This is achieved for the first time using regularisation techniques [1], applied to model toluene-in-water emulsions. Regularisation, based on both the distribution area and its summed second derivative, are compared. Several techniques to automatically select the optimal regularisation parameter are assessed: Y The L-curve method, Y Generalised Cross Validation (GCV) and Y The Discrepancy principle. The most robust regularisation implementation is identified for both the scenario when the overall error in the experimental measurements can be estimated and when it cannot. Velocity-compensated PFG techniques have also been used to size emulsion droplets under flowing conditions [2]. This is essential when the sample contains a distribution of velocities. Flow-compensated PFG has also been combined with imaging techniques, producing maps of droplet size in flowing emulsions. The technique has been applied to emulsions flowing in capillaries and pipes. In addition, various concentrated emulsions have been studied under shear in both a wide-gap and narrow-gap couette, a rheo-NMR device. This device enables the rheology of the emulsion to be determined, any droplet migration to be identified and surface slip properties to be evaluated over a range of shear rates.

References [1] Wilson JD. J Mater Sci 1992;27:3911. [2] Johns ML, Gladden LF. J Magn Reson 2002;1541:142. 2

H NMR investigation of urea and thiourea inclusion compounds of different substituted alkanes Thomas Handel, Klaus Mu¨ller Institut fu¨r Physikalische Chemie, Universita¨t Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany

Urea forms inclusion compounds with n-alkanes containing at least six carbon atoms [1]. Likewise, branched alkanes, for example with a 2-methyl group, can be incorporated if the chain length exceeds ten methylene units. Thiourea with its larger channel diameter (6.1 Å versus 5.25 Å in urea) allows the inclusion of even higher branched alkanes. In this contribution variable temperature 2H NMR sudies (lineshapes, relaxation experiments) of selectively deuterated 2-methyl-hexadecane in urea and thiourea in a temperature range between 110 K and 330 K are presented. Above 220 K the urea inclusion compound exhibits axially symmetric, motionally-narrowed 2H lineshapes. In fact, this can be understood by a fast rotation of the alkanes (in the almost trans conformation) around the channel axis. At the same time the lineshapes of the corresponding thiourea inclusion compound are further narrowed due to a higher degree of motional freedom in the larger channel. Computer simulations are performed in order to determine and to quantify the different underlying motional processes and ordering behav-

iour of the guest species (i.e. reorientational motions, conformational motions) under such confined conditions. The results are compared with the data from studies on linear alkanes [2–3] in order to demonstrate the influence of the particular guest structure on such molecular properties.

References [1] Schlenk W. Liebigs Ann Chemie, 1949, 204. [2] Greenfield MS, Vold RL, Vold RR. Mol Phys 1989;662:269. [3] Schmider J, Mu¨ller K. J Phys Chem A 1998;102:1181.

The formation factor as a feature of trabecular bone microarchitecture G. Guillot, F. Re´my, Th. Antoniadis U2R2M (CNRS UMR8081) Baˆt. 220 Universite´ Paris-Sud 91405 Orsay Cedex France Trabecular bone strength is mainly determined by bone mineral density, however other trabecular architecture parameters could be discriminant in prediction of fracture risk, since structures of equivalent density but of different architectures have been shown to differ also in mechanical properties [1], possibly through network anisotropy [2]. The trabecular bone network and the marrow (pore) space are fully interconnected. When disposing of the 3d map of a trabecular bone sample, the formation factor F [3] can be easily assessed by random walk simulation. This factor has also been assessed from the long-time limit of MR diffusion measurements in porous media [4]. In this study, we have examined the correlation between F and parameters commonly used in the characterisation of trabecular bone architecture, from high resolution MR images of 25 cylindrical samples taken from human calcaneus. Micro-MR images were acquired with a 3d spin echo sequence (TE/TR 8/200 ms) on a 8.5 T (360 MHz proton Larmor frequency) MRI microscope prototype developed in the laboratory, yielding a 128 ⫻ 128 ⫻ 256 matrix with a nominal isotropic resolution of about 66 ␮m and a signal to noise of about 17. Images were segmented into black (bone) and white (pore) with an iterative algorithm [5]. The bone volume fraction (BVF ⫽ bone volume/total volume) is complementary of the porosity. The formation factor was numerically computed from random walk simulation in the pore space, with several thousand independent walkers to ensure statistical accuracy, and a long-time limit attained after about 3 104 steps [3]. The network anisotropy was evaluated from the angular dependence of the Mean Intercept Length, fitted to an ellipsoid surface [6]; from the 3 principal lengths (MIL1⬍ MIL2 ⬍ MIL3) thus obtained, the anisotropy ratio Rmin ⫽ MIL1/MIL3 was the most representative of sample anisotropy. The 25 samples covered a large BVF range (8 –25%, from the MR evaluation). F showed a relatively high correlation (R2 ⫽ 0.87) with BVF, and increased with BVF, varying in the range 1.2–2.7. The anisotropy ratio Rmin was in the range 0.6 – 0.83, decreasing with BVF, but with a poor correlation (R2 ⫽ 0.36), while among various other parameters, F showed the highest correlation with Rmin (R2 ⫽ 0.58). It was checked that these conclusions were not changed when the microarchitecture parameters were computed from high-resolution X-ray images of the same samples [7]. These results suggest that F could be related to trabecular bone anisotropy, and that MR-based global measurements (diffusion coefficient, relaxation times) less demanding in system performance than imaging at a microscopic resolution could thus be of interest in the assessment of trabecular bone anisotropy.

References [1] Kleerekoper M, Villanueva AR, Stanciu J, Sudhaker RD, Parfitt AM. Calcif Tissue Int 1985;37:594 –7. [2] Turner CH. J Biomech 1992;25:1–9.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 [3] Antoniadis Th, Scarpelli J-P, Ruaud J-P, Gonord P, Guillot G. Osteoporosis Intern 1998;8:517. [4] Mair RW, Wong GP, Hoffmann D, Hurlimann MD, Patz S, Schwartz LM, Walsworth RL. Phys Rev Lett 1999;83:3324 –7. [5] Antoniadis Th, Scarpelli J-P, Ruaud J-P, Gonord P, Guillot G. Med Image Anal 1998;3:119 –28. [6] Harrigan TP, Mann RW. J Mater Sci 1984;19:761–7. [7] Last D, Peyrin F, Guillot G. 2002 private communication.

Displacement/relaxation correlations as a probe of structure in porous media: experimental and theoretical studies of simple model systems Melanie M. Brittona, Robin G. Graham, Ken J. Packer aDepartment of Chemical Engineering, University of Cambridge, Cambridge CB2 3RA United Kingdom bSchool of Chemistry, University of Nottingham, Nottingham NG7 2RD United Kingdom In recent work we have demonstrated that, by using a combined PGSTE/ CPMG pulse sequence, it is possible to obtain a spatially-resolved view of surface-mediated relaxation processes in fluid flowing through a glass bead pack [1]. In this system multi-exponential relaxation behaviour was observed, which arose from diffusion of the pore fluid through inhomogeneous internal magnetic field gradients. It was found that in this “T1resolved propagator” experiment differing relaxation components could be associated with different displacements. The longest relaxation time mode had a displacement distribution, which looked similar to a typical flow propagator. The shorter T2 modes seemed only to exist over a limited range of displacements and showed a characteristic variation of T2 value with displacement, where longer T2 components were associated with longer displacements. A simple model of this system, where the slower moving streamlines are nearest the bead/pore interface and so experience stronger transverse relaxation by diffusion though internal gradients, would explain this observation. In order to assist interpretation of these results and to get a better representation of the underlying processes involved in this and similar systems we have undertaken analytical work based on the theory of Brownstein and Tarr [2]. This theory describes how diffusion to an active sink can lead to multiexponential relaxation behaviour of the nuclear spins in fluids contained within porous media. Our work has extended this theory to correlate such relaxation behaviour with displacements in a fluid undergoing laminar flow in a glass capillary. Experimental work on this system has also been done and comparison with the predictions of the analytical solution was possible

References [1] Britton MM, Graham RJ, Packer KJ. Mag Reson Imag 2001;193– 4: 325–31. [2] Brownstein KR, Tarr CE. Phys Rev A 1979;19:2446.

Microstructural characterisation of liquid oil distributions in fractionated edible oils G. J. W. Goudappel, J. P. M. van Duynhoven Unilever Research & Development Vlaardingen, PO Box 114, 3130 AC Vlaardingen, The Netherlands A common technique for oil/fat fractionation is the separation of the solidified fat by filtration of the oil under pressurised conditions. The efficiency of this process is governed by the porous properties of the solid filter cake, which consists of fat spherulites, solid particles and oil. To understand the physical limitations of this technique it is important to know how the liquid and the solid are structurally distributed. Time domain NMR relaxation, Cryo-SEM and CSLM techniques were used for identification of the different oil regions, which could be assigned to continuous, inter - and intra particle pore regions. NMR diffusion was

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used to probe the average pore spaces (dimensionality) as function of the Solid Fat Content, which showed a decrease for increasing SFC. The spatial distribution of the solid and the liquid was resolved using 1D MRI-single point and Strafi imaging. Inhomogeneous distribution of AI sites in nano-zeolite ␤ as probed by 27AI 5QMAS NMR A. Goldbourt1, M. Talianker2, S. Vega1 Chemical Physics Department, Weizmann institute of Science, Rehovot 76100 Israel Department of Materials Engineering, Ben-Gurion University of the negev, Be’er Sheva, Israel Zeolite ␤ is a well known catalyst, used in numerous applications such as cracking, hydrocracking, dealkylation and more. Catalytic reactions normally take place at acidic surface sites, created by the substitution of Si by an Al atom, thus requiring the presence of compensating cations such as protons, sodiums and others. Upon reduction of crystal size, the catalytic activity of zeolite b, as of other zeolites, increases due to the larger accessibility of active surface sites. Characterization of these sites is therefore important as part of the investigation of such materials. The active sites are conveniently probed by 27AI solid state NMR, since AI has a nuclear spin (I ⫽ 5/2) and its abundance is 100%. The local environment of aluminum atoms can be probed even at very small Al concentrations and recently, with the introduction of the multiple-quantum magic-angle-spinning (MQMAS) technique, it has become possible to distinguish between Al atoms with the same coordination, even at relatively low magnetic fields. We have measured the high-resolution aluminum spectra of zeolite ␤ (Si/AI ⫽ 25) with large, medium and nano particle sizes by using the 5QMAS experiment utilizing our recently developed sensitivity enhancement schemes. Two tetrahedral sites were resolved clearly in the large size particles, which were attributed to atoms at the pore walls surface and atoms in the bulk. Upon reduction of the crystal size, Al atoms tend to occupy the bulk sites rather then those on the pore wall.

Characterisation of the structure foams by means of MRI J. Go¨tz, N. Eisenreich, A. Geißler, E. Geißler, A. Kauffmann Lehrstuhl fu¨r Brauereianlagen und Lebensmittel-Verpackungstechnik, TU Mu¨nchen/Weihenstephan, Weihenstephaner Steig 22, 85350 FreisingWeihenstephan, Germany Fraunhofer Institut fu¨r Chemische Technik (ICT), Joseph von Fraunhofer Str. 7, 76327 Pfinztal, Germany Polymer foams are used in many technological fields. For example, vibration-sensitive products are often cushioned by polymer foams. The damping behaviour and the energy absorption mechanism of foam depends on the microscopic cellular structure. Foams under compression loading have characteristic stress-strain curves with three typical regions. The deformation mechanism in this regions are linear elasticity, collapse and densification. Linear elasticity is controlled by cell wall bending. When loading is compressive the plateau in the stress-strain curve is associated with the collapse of the cells by buckling. If the cell walls have almost completely collapsed, opposing cell wall touch and further strain compresses the solid itself, giving the final region of rapidly increasing stress. The Young’s modulus (moduls of elasticity) and the plateau stress is related to the density of the foam. Increasing the density of the foams increases the Young’s modulus, raises the plateau stress and reduces the strain at which the densification starts. With MRI the foam structure can be analyzed. It is possible to observe the deformation behaviour of the cell structure of a foam in situ. A compression loading-experiment was conducted in the magnet and observed by MRI. The poster shows the results of the deformation experiment and the analysis of the deformation behaviour by image processing.

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Dynamics in guest-host systems by using solid state 2H NMR Jorge Garibay, Klaus Mu¨ller Institut fu¨r Physikalische Chemie, Universita¨t Stuttgart, Germany Pfaffenwaldring 55, D-70569 Stuttgart, Germany

intensity pulsed field gradients while at the same time retaining spectral resolution. The procedure consists of three steps: 1. Measurement of a possible mismatch of the pulsed field gradient by detecting the spin echo in the presence of a read gradient, 2. correcting for this mismatch by changing the read gradient during the preparation period, and 3. acquisition of chemical shift resolved spectra without the read gradient during the detection period.

2

H NMR spectroscopy (lineshape and relaxation experiments) has been carried out to study the molecular behavior of cyclophosphazene—C6D6 (CPZ-C6D6) and ALPO4-5—C6D6. The experimental 2H NMR spectra in the CPZ-C6D6 inclusion compounds recorded at room temperature, indicate the presence of highly mobile guest species. Upon cooling of the sample typical lineshape effects occur in the region of 120 K which can be attributed to a slow-down of the reorientation of the guest molecules around the cyclophosphazene host channels. In fact, at about 80 K this motion is slow on the NMR time-scale. At the same time, the rotation of the benzene molecules around their C6-axes can be followed down to much lower temperatures; this motion is still visible at 20 K. In addition, below 30 K a solid-solid phase transition occurs which is also reflected in the 2H NMR lineshapes and the relaxation data. A quantitative analysis of the experimental data is achieved by computer simulations taking into account the above-mentioned motions of the benzene guests. This gives access to the activation parameters of the various molecular processes. In addition recent results from studies on ALPO4-5—C6D6 are presented as well. Again it is found that the guest molecules are high mobile and undergo various types of overall motions which can be followed by the NMR lineshapes and relaxation experiments.

Monitoring low self-diffusion coefficients of mixtures adsorbed in zeolites by FT PFG NMR with ultra-high pulsed field gradients Petrik Galvosas, Stefan Gro¨ger, Frank Stallmach, Jo¨rg Ka¨rger Fakulta¨t fu¨r Physik und Geowissenschaften, Universita¨t Leipzig, Germany In NMR studies of adsorbed species in zeolites one usually observes broad NMR lines corresponding to small transverse relaxation times (T2 and T*2) as well as low translational mobilities [1]. Under such conditions, measurements of self-diffusion by PFG NMR demand the application of short and high intensity pulsed field gradients. However, the use of high gradient intensities requires procedures to match the field gradient intensities [2,3] which in turn often prevent the acquisition of high-resolution NMR spectra. In the present paper we propose a method for matching ultra-high

The outlined procedure is applied to monitor intra-crystalline selfdiffusion of a n-butane/benzene mixture in zeolite NaX by the 13-interval PFG NMR pulse sequence [4]. Distinct lines for benzene and n-butane in the 1H NMR spectra, which are not distorted by a mismatch of pulsed field gradients as recently reported by Price et al. [2], are observed for pulsed field gradient intensities of up to 20 T/m. The matching procedure in conjunction with ultra-high pulsed field gradient intensities allows FT PFG NMR measurements of self-diffusion coefficients as low as 10⫺12 m2/s as, e.g., observed for benzene in the present system (Fig. 1).

References [1] [2] [3] [4]

Ka¨rger J, Pfeifer H. Zeolites 1987;7:90. Price WS. J Magn Reson 1999;139:205. Galvosas P. J Magn Reson 2001;151:260. Cotts RM. J Magn Reson 1989;83:252.

Fringe-field diffusometry of polymer melts of high molecular weights in nanopores E. Fischer, U. Beginn, R. Kimmich Sektion Kernresonanzspektroskopie, Universita¨t Ulm, Ulm, Germany The dynamics of polymer chains confined to artificial tubes formed by the pores of a nanoporous material should display all the features predicted by the reptation model [1], provided that the polymer/wall interaction does not lead to adsorption effects. The central question is how chain dynamics changes if the motion of the polymer is restricted by theses solid obstacles. In a melt, the dynamic restrictions on a given polymer are imposed by the surrounding neighbours and, consequently, are only present for a

Fig. 1. Chemical shift resolved signal attenuation as a function of the applied pulsed magnetic field gradient intensity measured with the 13-interval pulse sequence. The self-diffusion coefficients calculated from the slope of the fitted data are (1.03 ⫾ 0.04)⫻10⫺11 m2/s for n-butane and (2.94 ⫾ 0.05)⫻10⫺12 m2s for benzene at a observation time ⌬ ⫽ 25 ms.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 limited time known as the tube disengagement time. For a polymer melt in a porous medium, on the other hand, only the motion along a curvilinear fixed path given by the porosity of the host matrix is possible. Contrary to the melt, the obstacles in this case are represented by the walls between the host molecules and the polymer chains comprising the remaining pore space. Consequently, a behaviour similar to region III of the tube/reptation picture is expected. In order to study the dynamic interaction between a given chain and its restricting wall, the investigated polymer should be of high molecular weight, i.e. chain-end effects can safely be neglected. The porous matrix, on the other hand, should consist of a material with narrow elongated pores of preferably cylindrical diameter. A material that fulfils these requirements is generated by the polymerisation of a monomer solution of hydroxymethylacrylate containing polyethylene oxide [2]. Cooling down a homogenous solution of polyethylene oxide in hydroxymethylacrylate monomers spinodal phase separation takes place and creates phase boundaries between the polymer and the monomer molecules. The polyethylene oxide in the polymer-rich phase vitrifies and can be preserved by subsequent polymerisation and cross-linking of the monomers to build the later matrix of polyhydroxymethacrylate. Elevating the temperature above the melting temperature of the polymer leads to the situation in focus: a polymer melt moving in a nanoporous solid matrix. Fringe field diffusometry has been performed on polyethylene oxide melts in porous material prepared as previously described [3]. The influence on molecular dynamics by the presence of the solid tube wall compared to neighbouring chains in the melt is under consideration.

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also obtained and studied in artificial bilayered membranes composed of lipid/cholesterol mixture in the definite ranges of concentrations and of temperatures. Membrane formation promoted by purely physical interactions between lipids. Planar supported bilayered lipid membranes are the convenient models to study structure, interactions and molecular mobility in “rafts.” Translational molecular mobility in “raf”-containing samples remain one is attractive and less studied areas. We investigated self-diffusion in macroscopically aligned lipid bilayers prepared from binary or ternary mixtures of sphingomyelin, dioleoyl phosphatidylcholine, dimyristoyl phosphatidylcholine and cholesterol. Self-diffusion was measures by pulsed field gradient NMR technique at 100 MHz using a Varian/Chemagnetics CMX Infinity spectrometer, equipped with a purpose-built goniometer probehead (Cryomagnet systems, Indianapolis). Information about phase state and phase transitions was obtained from differential scanning calorimetry data using VP-DSC microcalorimeter (MicroCal Inc., Northampton, MA). Our investigation showed, that in the presence of membrane domains bilayers demonstrate an effects, which typical to heterogeneous substances. The temperature dependence of self-diffusion coefficient (D) became anomalous, widths of distribution of D increases up to three times, D became time dependent in the way typical to restricted diffusion. Analysis of the change of shape of spectra, which obtained after Fourier transformation of stimulated echo, allows to divide self-diffusion coefficients related to molecules inside and outside “rafts.”

Restricted diffusion in porous beads studied by PGSE NMR Fredrik Elwinger, Marie Wulff, Bo Medhage Amersham Biosciences, Bjo¨rkgatan 30, SE-751 84 Uppsala, Sweden

References

In liquid chromatography, biomolecules are separated in columns packed with porous beads, typically 5–200 mm in diameter and with pore dimensions ranging from approximately 10 –200 nm. The pore structure is important for the molecular mobility in such systems and is critical for the performance of the separation. There are a variety of techniques available for characterisation of porous materials that can be dried without drastically changing the pore structure, e.g. inorganic materials (like silica and zirconia) and many polymer materials (like polystyrene). However, for characterisation of hydrogels (like agarose gels), methods are scarce. One of the most frequently used methods for particle gels is gel filtration, also known as size exclusion chromatography (SEC). In this work, pulsed gradient spin echo (PGSE) NMR is used for characterisation of porous agarose gel particles and a comparison is made with results obtained from SEC and electron microscopy. The effective diffusion coefficients of a number of molecular probes (including proteins, polyethylene glycols and water) were measured within gels with different

[1] Doi M, Edwards SG. Theory of Polymer Dynamics, Clarendon Press, Oxford, 1986. [2] Beginn U, Fischer E, Pieper T, Mellinger F, Kimmich F, M, Mo¨ller R. J Polym Sci A Polym Chem 2000;38:2041–56. [3] Fischer E, Kimmich R, Beginn U, Mo¨ller M. J Phys Rev E 1999;59: 4079 – 84.

Domain formation and lateral self-diffusion in lipid bilayers Andrey Filippov, Greger Ora¨dd, Go¨ran Lindblom Department of Biophysical Chemistry, Umeå University, SE-90187 Umeå, Sweden A growing body of evidence shows that cholesterol rich domains (“rafts”) of sphingolipids and glycosphingolipids are present in the membranes of cells. The existence of rafts influences on the biomembrane functions, on the presence of special subset of membrane proteins, involved in signal transduction, lipid trafficking and transcytosis. These type domains can be

Fig. 1.

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pore structures. The diffusion time in the NMR experiment was varied to obtain information from different length scales in the samples. The results show that PGSE NMR is a powerful tool for characterising the porosity of hydrogels and the diffusion coefficients correlate well with data obtained from SEC. An advantage of using particle systems for studying restricted diffusion is the very short time needed for reaching equilibrium in the porous system due to the short diffusion distances in the beads. Furthermore, it is also relatively easy to make beads with a homogeneous pore structure. However, an issue associated with this type of system is the interstitial pore space formed between the beads. When the beads are packed in a chromatography column this void volume is of relevance since it is part of the overall pore system and should thus be included in the studies. Nevertheless, in other situations the void pore system may complicate things and must be handled in some way. Various approaches of addressing the void space issue are presented here.

PFG NMR studies of single- and multi-component diffusion in porous alumina catalyst support pellets Catherine Clayton, Mick Mantle, Lynn Gladden University of Cambridge, Department of Chemical Engineering, Pembroke Street, Cambridge CB2 3RA, United Kingdom While there now exists a substantial literature on the diffusion of pure liquids in porous media, relatively little work has been done addressing multi-component liquid diffusion within such materials. The present study addresses this area of research in the context of understanding molecular transport within porous catalyst support pellets. The motivation for the work comes from the fact that in many industrial heterogeneous catalytic reactions a solvent is often used, either to dissolve the reactant or to improve the yield of desired product and rate of reaction. Despite the observed dependence of the process performance on the solvent used, there exists no basic understanding of how a particular solvent influences a given chemical reaction. Previous workers have usually addressed the chemical implications of introducing a solvent to the reaction system. In contrast, we are investigating the influence of the solvent on the mass transfer processes within the catalyst pellet. The research presented here forms part of a detailed study of single- and multi-component diffusion within porous aluminas with a range of pore sizes over at least four orders of magnitude and a mean pore size of around 700Å. The NMR diffusion data are used to gain insight into reactor performance when chemical conversions are performed with each of the solvents studied in the NMR experiments. The system chosen for study is the conversion of tert-butyl phenol to tert-butyl cyclohexanol. The solvents used are a series of alcohols: methanol, propan-1-ol, propan-2-ol, hexan-1-ol, octan-1-ol and decan-1-ol; and a series of alkanes: hexane, octane and decane. Results will be presented as follows: Y A detailed study of the molecular self-diffusion characteristics of the pure solvents as bulk liquids and within the pore structure of the catalyst pellets. The behaviour of the log-attenuation curve is investigated and analysed as a function of the pulse sequence used. In particular, the influence of internal gradients arising from varying magnetic field gradients within the porous material on the measurement is investigated. The results to be presented will show that pulsed gradient techniques are able to discriminate between the influences of molecular size and reactive group associated with the hydrocarbon on molecular self-diffusivity within the pore structure. The Tanner stimulated echo pulse-field gradient sequence [1] is used, along with the modified 13 interval sequence suggested by Sorland, et al [2]. Y Binary mixtures of reactant, and solvent have been studied both as a function of mixture concentration, and temperature. The diffusion of both species can be studied and activation energies to the molecular diffusion are obtained and compared to the behaviour of pure aluminas. To enable discrimination between molecular species

within the porous solids, NMR studies employing 13C as well as 1H observation have been employed. solvent. Data will be presented for both bulk liquid diffusion and diffusion in the porous aluminas. To enable discrimination between molecular species within the porous solids, NMR studies employing 13C as well as 1H observation have been employed.

References [1] Tanner JE. J Chem Phys 1970;52: 2523– 6. [2] Sorland GH, Hafskjold B, Herstad O. J Magn Reson 1997;124:172– 6.

Effect of Water and Ammonia on the local structure of aluminum in the Silicoaluminophosphates H-SAPO-34 and H-SAPO-37 studied by in situ MAS NMR spectroscopy Andreas Buchholz, and Michael Hunger Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany Due to their acidic properties and form selectivity, microporous silicoaluminophosphates find an increasing interest as solid catalysts in chemical technology [1–3]. The stability of rehydrated template-free silicoaluminophosphates shows substantial differences. In the case of H-SAPO-34, the presence of water influences the X-ray patterns indicating a strong loss of crystallinity which is completely restored after a dehydration at 823 K [4]. Briend et al. [5] explained the loss of crystallinity upon hydration of SAPO-34 by breaking of Si-OH-Al bonds. Hydration of H-SAPO-37 at room temperature causes irreversible structural changes and leads to a material which is totally amorphous to X-ray diffraction, while at temperatures of more than 345 K, template-free H-SAPO-37 exhibits a high stability towards hydration [6]. In the present work, modern in situ MAS NMR spectroscopy was applied to investigate the framework changes or damages in silicoaluminophosphates towards ammoniation/hydration followed by dehydration of H-SAPO-34 and H-SAPO-37. These investigations were carried out applying a 4mm Bruker VT MAS NMR probe modified with a gas injection system [7]. During the in situ MAS NMR experiments, a flow of dry nitrogen (25–50 ml/min, carrier gas, dehydration) loaded with water vapor having a partial pressure of p(H2O) ⫽ 2.3 kPa (hydration) or mixed with ammonia (ammoniation of acid sites) was injected via a glass tube into the spinning MAS NMR rotor. 1 H MAS NMR spectra of the dehydrated materials recorded before starting the gas injection consists of signals due to bridging SiOHAl groups and SiOH and/or POH groups. After starting the hydration, a significant decrease of the signal of SiOHAl groups occurs accompanied by the appearance of a broad signal of water molecules. Until the adsorption of about 1 H2/SiOHAl, no change of the 27Al MAS NMR spectra could be observed. First upon a higher water adsorption, the formation of octahedrally coordinated aluminum species was indicated. The dehydration of the hydrated H-SAPO-34, performed with dry nitrogen (carrier gas), led to a significant decrease of the octahedrally coordinated framework aluminum in the 27Al MAS NMR spectra even at 295 K. In the case of H-SAPO-37, the signal of octahedrally coordinated aluminum disappeared by purging with nitrogen at 373 K. While the hydration induced framework change of H-SAPO-34 is nearly reversible, since the water molecules are only weakly physisorbed, the hydration of H-SAPO-37 led to an irreversible change of the aluminum coordination. The 1H MAS NMR spectra of H-SAPO-34 loaded with ammonia and followed by adsorption of water are shown in Scheme 1. In the beginning of the ammoniation, the formation of ammonium cations (⬃6 ppm) occurred. After adsorption of about 3 NH3/SiOHAl, octahedrally coordinated aluminum species are indicated, and the 1H MAS NMR signal shifts to 7 ppm with increasing ammonia loading. Purging of the sample with dry nitrogen at temperatures of 373– 413 K led to a decrease of the signal of ammonia, the signal of octahedrally coordinated aluminum species disappeared. Upon rehydration, the octahedrally coordinated aluminum species

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450

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Combining MRI and X-ray CT for reservoir rock characterization: the rock chemistry fluid distribution imaging (RCFDI) method A.W. Bidar1, F. Stallmach2, T. Eidesmo3, J. Attard2, H. Rueslåtten3, S.H. Midtlyng4, T. Singstad2, A. Johnsson1 1Faculty of natural science and technology, Dept. of physics, MR Center, NTNU, Trondheim, Norway 2Sintef Unimed, MR Center, Trondheim, Norway 3Statoil Research Center, Trondheim, Norway

Scheme 1. 1H MAS NMR spectra of H-SAPO-34 loaded with NH3, purged with N2 (11nd spectra) and loaded with H2O.

show up again and a shoulder at high field in the 1H MAS NMR spectra indicates water, which does not replace the ammonia at the SiOHAl sites.

References 1. M Sto¨cker. Microporous Mesoporous Mater. 29, (1999), 3. 2. JA Martens, PJ Grobet, PA Jacobs. J. Catal. 126, (1990), 299. 3. HB Mostad, M Sto¨cker, A Karlsson, T Rorvik. Appl. Catal. A: General 144, (1996), 305. 4. C Minchev, Y Neiska, V Valtchev, V Minkov, T Tsoncheva, V Penchev, H Lechert, M Hess. Catal. Lett. 19, (1993), 125. 5. M Briend, R Vomscheid, MJ Peltre, PP Man, D Barthomeuf. J. Phys. Chem. 99, (1995), 8270. 6. M Briend, A Shikholeslami, MJ Peltre, D Delafosse, D Barthomeuf. J. Chem. Soc., Dalton Trans., (1989), 1361. 7. M Hunger, M Seiler, T Horvath. Catal. Lett. 57, (1999), 199.

Al2O3-H2O suspensions as porous media: NMR investigations of structure and transport Detlef Bork, Manfred Holz Institut fu¨r Physikalische Chemie, Universita¨t Karlsruhe, Kaiserstr. 12, D-76128 Karlsruhe, Germany Al2O3-H2O suspensions are widely used in ceramics processing and the design of sophisticated ceramic devices. Whereas the strong dependence of the rheological properties from, e.g., the pH value can be utilized to prepare suspensions with high solids content the underlying structural features are far from being well understood. From the NMR point of view these systems can be regarded as porous media. In contrast to many standard rheological techniques NMR is able to investigate the suspensions under static, i.e. non-driven conditions. Beneath water being an inherent constituent of the suspension the water molecules serve as molecular probes for the structure of the solid matrix. Concerning the respective length scales under investigation on various suspensions we performed complementary 1 H-spin-lattice relaxation (SLR) measurements, yielding information about the surface-to-volume ratio S/V, and dynamic imaging, giving the system’s tortuosity ␶. We examined, e.g., the dependence of S/V and ␶ upon the following parameters: pH value between the maximum zeta potential (at approx. pH 4) and the iso-electric point (at approx. pH 9), solids content (10 to 50 vol.%), salt concentration (0,1 to 1,0 mol/l NaCl or NH4Cl), particle size, impurities etc. Furthermore, we observed the sedimentation process in-situ in order to correlate SLR-time, signal amplitude and integral to the actual solids content. From these comprehensive studies we are able to derive first structural models.

Backgrounds MRI and X-ray CT are complementary techniques, and some researchers have long felt that the combination of the two techniques could be a powerful factor in the investigation of, for example, possible correlations between wettability and mineralogy in petroleum reservoir rock. Some attempts have been made in the past to combine the two techniques for petrophysical applications, but images have usually just been compared visually without any attempt to combine images in a quantifiable way. We have developed the tools and methodologies for generating quantitative image data from rock samples on the same slices and orientation by combining quantitative MR images (QMRI) and quantitative X-ray CT images (QCT). These methods were applied to the characterization of a homogeneous sandstone (Bentheimer). Bulk density (␳) and effective atomic number (Zeff) were generated by QCT. From the same slice and orientation, T1 relaxation and proton density maps were generated using QMRI. Porosity maps from the two imaging modalities were also assessed. Methods MRI was performed at 10MHz using a 31 cm horizontal bore superconducting magnet (Maran 10, Magnex Scientific, Oxford, England). X-ray CT was performed on a Siemens Somatom DR. All images were transferred to a PC and further processed by using the IDL (RSI, Kodak, Co.) software. In order to interrogate precisely the same-slice and orientation of the two imaging modalities, the following tools were build: a non magnetic MRI/X-ray CT compatible core holder; a core holder support; a motorized core table trolley for the MRI scanner and a MRI/CT compatible reference phantom used as a QA/QC tool which fit into the core holder. Bulk density and effective atomic number were generated by means of the dual energy technique. Briefly, this technique takes into account the energy, density and atomic composition dependency of the attenuation of X-ray photons. This is done by expressing the mass attenuation coefficient (␮m) as a linear combination of the Compton and photoelectric cross sections. T1 and proton density mapping was obtained using a 2D saturation recovery spin echo sequence (SR-SE). A set of 15 T1-weighted images were recorded varying the recovery time from 1 ms to 10s. Relaxation data were fitted to a mono-exponential using the Levenburg-Marquard least squares algorithm. Porosity images proceeding from the same slice were calculated using density images in the dry and 100% brine saturated state and by proton density images. Results The tools and methodologies developed for same-slice and orientation imaging were successfully conceived and tested on a reference phantom. Models and method used to obtain ␳ and Zeff by mean of QCT on a range of test materials and the homogeneous rock sample showed a good agreement with theoretical values (see Table 1). Proton density and T1 maps from the same slice were generated. Comparing the mean porosity fraction (⌽) obtained by QCT (⌽OCT⫽ 0.256) and QMRI (⌽OMRI ⫽ 0.267), it can be concluded that both methods predict equivalent porosity. On the other hand the distribution of the porosities is slightly different. The ⌽OCT histogram showed a larger spread in the distribution of the porosities. This spread is mainly attributed to an increase in the amount of beam hardening in the saturated sample over the dry sample due to an increase of density by the presence of brine. T1 distribution showed a broad distribution with T1 values ranging from 0.69 –1.17s (mean: 909 ⫾ 66 ms). As expected, the shape of the distribution is monomodal. This is mainly reflecting a homogeneous rock sample. Conclusion The novel method combines two complementary quantitative imaging techniques and provides a versatile tool for probing spatially the rock chemistry and mineralogy as well as fluid and/or pore size distributions. The effective atomic number and density images are related to the chemistry and mineralogy of the rock which influences on wettability

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Table 1 Mean density ␳QCT and effective atomic number ZeffQCT for various materials derived from region of interest (ROI) of ␳ and Zeff images Material

␳theor[g/cm3]

␳QCT[g/cm3]

Zefftheor

ZeffQCT

Graphics (C) Teflon Aluminum (Al) Alsinth (Al2O3) Bentheimer dry Bentheimer brine sat

1.70 2.16 2.70 3.96 2.11 -

1.68 2.08 2.74 3.97 2.15 2.43

6.0 8.49 13.0 11.30 10.80 -

6.21 8.70 12.95 10.70 10.70 10.38

and fluid distribution. Proton density images show the spatial distribution of fluid-filled porosity and T1 images are related to the physical nature of the pores. Thus, the RCFDI method should help to detect spatially inhomogeneous wetting properties of rocks and hence lead to fundamental insight into the fluid flow properties of reservoir rocks.

* Corresponding author. [email protected] (A. Bidar) Solid-State NMR Spectroscopical Study of the Conversion of a Dry Gallosilicate Gel to Zeolite [Ga]Beta and Characterization of the obtained [Ga]Beta zeolites Andreas Arnold, Michael Hunger, and Jens Weitkamp Institute of Chemical Technology, University of Stuttgart, D-70550 Stuttgart, Germany Zeolites are usually prepared using the hydrothermal synthesis method. In 1990, a new technique for synthesizing zeolites was proposed. It consists of the conversion of a dry aluminosilicate gel by contact with water and volatile amines (vapor-phase transport, VPT) [1]. When non-volatile amines are used as templates, they are incorporated into the dry gel and only water is supplied from the gas phase (steam-assisted conversion, SAC) [2]. The steam-assisted conversion technique was applied for the preparation of [Ga]Beta zeolites with nSi/nGa-ratios between 8 and 37. The preparation of the dry gallosilicate gel and its conversion to [Ga]Beta zeolites is described in detail in Ref. [3]. In the present work, the obtained samples as well as the conversion process of the dry gel to [Ga]Beta zeolites were investigated by solid-state NMR spectroscopy. Scheme 1 shows the conversion process of the dry gallosilicate gel to zeolite [Ga]Beta (nSi/nGa ⫽ 37) at 180°C during 3 days. The 29Si HPDEC MAS NMR spectrum of the XRD-amorphous dry gel (after 0 h) shows signals at ⫺87 and ⫺96 ppm, which can be assigned to Q2 and Q3 species, respectively. The signals at ⫺106 and ⫺111 ppm are due to Q4 species. After 17 h, the sample has a crystallinity of 60%. The corresponding 29Si

Scheme 1.

HPDEC MAS NMR spectrum shows a signal from ⫺114 to ⫺111 ppm due to Si(0Ga) species (Q4) and a line at ⫺101 ppm, which is caused by a superposition of the signals of Si(1Ga) species (Q4) and SiOH groups (Q3). These changes can be explained by the condensation of SiOH groups. After 65 h, the crystallinity amounts to 100%. The corresponding 29Si HPDEC MAS NMR spectrum shows two signals at ⫺111 and ⫺101 ppm with a higher relative intensity of the latter signal, indicating a further incorporation of gallium into the framework of zeolite [Ga]Beta. The incorporation of gallium into the framework of zeolite Beta was proved by the application of 1H, 29Si HPDEC and 71Ga MAS NMR spectroscopy. The 71Ga MAS NMR spectra of the as-synthesized samples show only a single signal at 155 ppm which is assigned to tetrahedrally coordinated gallium on framework positions. After calcination at 450°C in N2 or air and rehydration, the spectrum of the sample with the highest gallium content (nSi/nGa ⫽ 8) shows an additional 71Ga MAS NMR signal at ⫺10 ppm due to octahedrally coordinated gallium on extra-framework positions. A quantitative evaluation of the 29Si HPDEC and 1H MAS NMR spectra yields, that up to 30% of the framework gallium atoms are removed from their tetrahedrally coordinated positions during calcination. The strength of the Br°nsted acid sites in zeolite H-[Ga]Beta (nSi/nGa ⫽ 8) was characterized by the adsorption of 13C-2-acetone (99% enriched) as probe molecule. The signal at 219 ppm in the 13C HPDEC MAS NMR spectrum indicates a lower Brønsted acid strength of the H-[Ga]Beta zeolite in comparison with zeolite H-[Al]Beta (221 ppm).

References [1] W Xu, J Li, J Li, F Wu. J. Chem. Soc., Chem. Commun. (1990) 755–756. [2] P.R.H.P.Rao, M Matsukata. Chem. Commun. (1996) 1441–1442. [3] A Arnold, M Hunger, J Weitkamp. Chem. Ing. Tech. 73 (2001) 1588 –1592.

Vapor diffusion contribution to molecular mobility inside Vycor porous glass I. Ardelean1,*, S. Wonorahardjo2, R. Kimmich2 1Technical University, Physics Department, 3400 Cluj-Napoca, Romania 2Sektion Kernresosonanzspektroskopie, Universita¨t Ulm, 89069 Ulm, Germany If a macroscopic sample contains a two-phase system formed of a liquid in thermal equilibrium with its vapor, the acquired NMR signals normally are entirely dominated by the magnetization of the liquid phase. The reason is that the density of the vapor phase at normal conditions is three orders of magnitude less than that of the same species in the liquid phase. Consequently the contribution to the signal from the vapor phase can be neglected. However, in some cases, diffusion measurements of liquids partially filling porous media indicate an enhanced self-diffusion coefficient as

Fig. 1. The dependence of the self diffusion coefficient of water and cyclohexane partially filing Vycor porous glass as a function of the degree of filling.

Abstracts / Magnetic Resonance Imaging 21 (2003) 421– 450 compared to the bulk phase [1–3]. One possible explanation for such observations can be the fast (relative to the NMR time scale) exchange process between the two phases: liquid and saturated vapor. Our recent results [4] on diffusion measurements for two test liquids water (polar) and cyclohexane (non polar) filling Vycor porous glass (average pores diameter of 4 nm) however indicated a dependence of the effective self diffusion coefficient on the degree of filling different from that expected from the scenario described in Ref. [1]. While the effective diffusion coefficient for water is decreased by reducing the liquid content it is increases for cyclohexane (see Fig. 1). Thus, a reduction of the water self diffusion coefficient occurs with reduced liquid content. Moreover the effective diffusion coefficient is smaller than its bulk value both for water and cyclohexane. The reason for such a dependence is considered to be the difference in the pore dimensions of the porous samples used in the previously reported experiments (bigger than 7 nm) and the present experiment (about 4 nm). The different dependence of water and cyclohexane molecules on the degree of filling can be explained by the fact that the water molecules are polar while the cyclohexane molecules are non-polar. The polar molecules have a stronger tendency to interact with the polar surfaces of the porous sample in comparison with the non-polar ones, and this should determine a different dependence of the effective self diffusion coefficient on the degree of filling. The Monte Carlo computer simulations we have done for model geometries confirm our experimental observations.

References [1] D’Orazio F, Bhattacharja S, Halperin P, Gerhardt R. Phys Rev Lett 1989;63:43. [2] Kimmich R, Stapf S, Callaghan S, Coy A. Magn Res Imag 1994;12: 339. [3] Valiullin RR, Skirda VD, Stapf F, Kimmich R. Phys Rev E 1997;55: 2664. [4] Wonorahardjo S, Ardelean I, Kimmich R. Pulsed field gradient NMR investigations of molecular diffusion in partially filled Vycor porous glass (in preparation).

VNMRF development of a virtual NMR facility Henrik W. Anthonsen, Geir H. Sørland, John G. Seland, Jostein Krane Frank Antonsen Håkon Rueslåtten Dep. of Chemistry, Norwegian University of Science and Technology, N-7034 Trondheim, Norway Statoil Research Centre, N-7005 Trondheim, Norway VNMRF (Virtual NMR Facility) is a system that uses Internet and Web technologies to provide a remote secure and direct acquisition control to an NMR instrument. The system includes also facilities that allows the retrieval and processing of data, to share notes and to collaborate with the local researchers. The motivation for developing the VNMRF-system is to facilitate collaboration between research groups that are situated at distant geographical locations. The system allows an informal, in-depth collaboration on work-in-progress on a specific dedicated NMR instrument without spending time and money to meet where the instrument is located. The concept of VNMRF includes a motivation to install the system at different locations, with different people and with instruments from various manufacturers. For this reason, it is crucial to design an expandable and customizeable system. To satisfy these needs, we have chosen a concept developed at the Environmental Molecular Science Laboratories (EMSL) in Richland, WA, USA. The present paper describes the VNMRF-system, our settings in different networks and the experience gained with the system regarding usability and network security.

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Laboratory and rotating-frame spin-lattice relaxometry of 8CB Aerosil Complex above the bulk isotropization temperature. Experiments and Monte Carlo simulations E. Anoardo1,*, F. Grinberg2, M. Vilfan3, R. Kimmich2 1FaMAF, National University of Co´rdoba, Co´rdoba, Argentina 2Sektion Kernresonanzspektroskopie, Uni-Ulm, Ulm, Germany 3J. Stefan Institute, Ljubljana, Slovenia Laboratory and rotating frame spin-lattice relaxation NMR experiments (T1,T1␳) were used to study the molecular dynamics and order in octylcyanobiphenyl (8CB) liquid crystal in bulk and confined in an aerosil network. The surface of these particles contains silanol groups that allow them to “polymerize”’ via hydrogen bonding and form a spatial network of silica strands. The silica surface induces order in the liquid crystal even above the nematic-isotropic transition. The surface-induced order is the largest at the liquid crystal –aerosil interface and decays exponentially with the distance, with a characteristic length equal to the nematic correlation length. Its value reaches a maximum at the nematic - isotropic transition, where it is typically about 20 nm. In the soft-gel 8CB-aerosil complex the average size of the voids between silica strands is much larger than the nematic correlation length. Therefore, surface-induced order is limited to a thin layer of molecules next to the interface, whereas the bulk-like isotropic phase extends over the major part of the void. When the liquid crystal is confined in aerosil networks, non-collective types of slow dynamics, based on surface ordering, become relevant. A two-phase fast exchange model distinguishing surface ordered and bulk-like phases was established for temperatures above the bulk isotropization temperature and tested with the aid of Monte Carlo simulations. Two relaxation processes could be identified. Reorientation mediated by translational displacements (RMTD) is a mechanism accounting for molecular reorientations due to the translational diffusion of molecules between surface sites with different orientations relative to the external magnetic field [1,2]. On the other hand, the number of molecules being subject to RMTD is reduced with time by exchange losses of molecules from the surface ordered phase to the bulk-like phase. The RMTD process tends to dominate at long times or low frequencies, whereas exchange losses (among restricted or unrestricted rotational diffusion regions) govern the spin-lattice relaxation dispersion at shorter times or higher frequencies. The cross-over between the two time regimes occurs at a characteristic exchange time determined by the populations of the two phases and the diffusion coefficient. It is accompanied by a cross-over from a linear to a square dependence of the relaxation rate on the surface population. The two-phase fast exchange model describes well the experimental spin-lattice relaxation dispersion data in spite of the strongly simplified assumptions on which the Monte Carlo simulations were based. The temperature dependence of T1␳was analyzed above the bulk isotropization transition in terms of the different dependencies on the fraction of the surface ordered phase expected for the RMTD and exchange loss regimes. The temperature dependence of T1␳ shows as well that both relaxation-inducing effects, RMTD and exchange losses, are important at frequencies of about 30 kHz. This is at variance to previous reports referring to the transverse spin relaxation in the liquid crystal 5CB in spherical droplets of a PDLC material, as well as in cavities of irregular shape in porous glasses. The difference might arise from different frequency windows under observation.

Acknowledgments Financial support by the Deutsche Forschungsgemeinschaft is acknowledged. E. A. thanks the Alexander von Humboldt Stiftung for a postdoctoral research fellowship. F. G. thanks the Ministerium fu¨r Wissenschaft, Forschung und Kunst Baden-W’urttemberg for a Habilitationsstipendium, and M. V. the Ministry of Education and Science of Slovenia for financial support.

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References [1] Liquid Crystals in Complex Geometry, Crawford P, Zumer S Eds., Taylor & Francis, Salisbury, 1996. [2] Kimmich R, NMR Tomography Diffusometry Relaxometry, SpringerBerlin, 1997.

Hydrogen NMR relaxation and diffusion in a porous building material during drying R. M. E. Valckenborg, J. Petkovic´, H. Huinink, L. Pel, K. Kopinga Eindhoven University of Technology, Department of Physics, P.O. Box 513, 5600 MB Eindhoven, The Netherlands In a porous building material normally large internal magnetic field gradients are present. These cause a rather complicated NMR signal decay for Hahn and stimulated echo pulse sequences. Recently we found that calcium-silicate brick (an isolation material) does not show any noticeable dephasing effect due to internal magnetic fields. This material is used in a 1D drying experiment. A sample that is fully saturated with water is sealed with Teflon at all sides, except for the top. At this side the sample is dried by blowing dry air over it. During the drying process, the hydrogen signal from the pore water is measured with NMR. From this signal, which can be measured quantitatively by a specialized scanner, the (local) moisture content can be deduced. The transverse relaxation time is measured with a CPMG pulse sequence with a short inter-pulse interval and hence free of dephasing effects. The longitudinal relaxation time is measured with a saturation recovery sequence. From these experiments it appeared that the longitudinal as well as the transverse relaxation time remained perfectly mono-exponential for all moisture contents from saturation down to almost zero, where no signal could be observed anymore. This indicates that the relaxation process is described by the so-called fast diffusion regime. The relaxation times were also found to depend linearly on the moisture content, which suggests that the pore structure of the material is such that also at very low moisture contents the surface to volume ratio of the pore fluid is small. Dephasing due to restricted diffusion in this material is investigated by two pulse sequences. For short times, the Hahn spin-echo intensity is affected by diffusion significantly. The decay is not described by classical free diffusion in a uniform effective filed gradient. For longer times, the stimulated spin-echo intensities are measured. The observed signal decay is mono-exponential for all drying times (i.e., moisture contents), just like the relaxation data. This experiment is performed at different gradient strengths. From these data the longitudinal relaxivity and the apparent diffusion coefficient have been obtained. The observed ADC does not depend on the echo time, but appears to increase with drying time. Probably in a non-saturated sample the remaining moisture experiences more local field gradients. As a first step to perform drying experiments on a porous building material with large internal magnetic field gradients (fired-clay brick) we investigated the NMR signal decay in the saturated material with Hahn, CPMG, and stimulated echo sequences. With the aid of a random walk simulation model, the observed signal decay is interpreted. This model can explain the dephasing effects present in a Hahn and in a CPMG pulse sequence. However, the stimulated echo measurements on this brick are more difficult to interpret, because the data at small echo times show large deviations from mono-exponential behaviour, which become more pronounced when the delay between the first 90 degrees pulses increases.

Micron-scale percolation structures Elke Kossel*, Rainer Kimmich Sektion Kernresonanzspektroskopie, Universita¨t Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany Understanding the properties of porous media is a challenge that attracts scientists in many different fields of research. Percolation structures are artificial porous media which are created by generating a random network

of occupied sites (pores) and unoccupied sites (barriers) on a previously defined grid. The transport characteristics of percolation structures are determined by the model used to calculate the structure and by the probability for a site of the grid being occupied. Therefore their mathematical description is much less complex than for a “natural” porous system [1]. For experimental verifications of the theoretical models, percolation model objects have been made and successfully characterized [2–5]. They were created mostly by using mechanical tools which restrict the minimum achievable pore size to a few 100 microns. Smaller pores are of interest because their transport properties are expected to be influenced by friction. We used Ultra Deep X-ray Lithography (UDXRL) to create percolation structures with a minimum pore sizes of a few tens of microns. This technique turned out to be favorable for this purpose because it allows the fabrication of structures with very high aspect ratios [6]. In this presentation we will give a description of the technique of UDXRL and we will present first results from measurements of transport characteristics in micron-scale percolation structures performed by Magnetic Resonance Imaging.

Acknowledgments Research carried out in part at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Division of Materials Sciences and Division of Chemical Sciences, under Contract No. DE-AC02–98CH10886. This work is supported by the Deutsche Forschungsgemeinschaft.

References [1] Bunde A, Havlin S (Eds.), Fractals and Disordered Systems, SpringerVerlag, Berlin 1996. [2] Klemm A, Mu¨ller HP, Kimmich R. Physica A1999242– 6. [3] Klem A, Kimmich R, Markus W. Phys Rev E 2001;63:041514. [4] Weber M, Klemm A, Kimmich R. Phys Rev Lett 2001;8619:4302– 05. [5] Kimmich R, Klemm A, Weber M. Mag Res Imaging 2001;19:353– 361. [6] Madou M. Fundamentals of Microfabrication, CRC Press; 1997.

Model studies of water dynamics on the MCM-41 surface via 2H double quantum filtered NMR Dennis W. Hwang, Lian-Pin Hwang Department of Chemistry, National Taiwan University, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan, Republic of China Dynamics of water adsorbed on MCM-41 has been investigated by 2H double quantum filtered (DQF) NMR and spin-lock double quantum filtered (SLDQF) NMR. From temperature dependent studies with various water loadings on MCM-41, it is found that there are different sites for water adsorption on MCM-41. The signal of water molecules in the slow site dominates in the observed DQF NMR. The influence of silanol groups on the MCM-41 surface strongly affects the motion of water molecules in the slow site, resulting in a residual quadrupolar interaction. As the signal of water in fast site dominates that observed in single quantum spectra, it also appears in DQF spectra through an exchange process. Moreover, with low water content on MCM-41, it shows that there is only single layer of water molecules on the surface. The interesting single layer water dynamics on the surface were carefully investigated by DQF and SLDQF NMR spectral analyses and T1 relaxation calculations. To interpret the single layer water dynamics on surface, modified cone model and reorientaion mediated by 2D jump diffusion model were employed in the analyses.

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Estimate of porosity length-scales in soils by MRI for microgravity plant growth experiments Daidzic N.E.†, Altobelli S.‡, Caprihan A.‡, Schimdt E.§, Alexander J.I.D.§ †National Center for Microgravity Research @ NASA John H. Glenn Research Center, 21000 Brookpark Rd., MS 110 –3, Cleveland, OH 44135, U.S.A., Email: [email protected] ‡New Mexico Resonance, 2301 Yale Blvd., SE; Suite C-1, Albuquerque, NM 871064237, U.S.A. §Case Western Reserve University, Crawford Hall 103, 10900 Euclid Avenue, Cleveland, OH 44106-7074, U.S.A. Soil can be best described as a unconsolidated granular media that forms porous structure. The present macroscopic theory of water transport in porous media rests upon two major postulates, first, on the continuum hypothesis that the physical properties of porous media can be associated with continuous, twice-differentiable field variables whose spatial domain is a set of centroids of Representative Elementary Volume (REV) elements. The second postulate states that the time-space dependence of the field variables can be represented in an integro-differential form of balance (transport) equations for mass, momentum, and energy. It follows that estimating proper time and length scales for averaging and derivation of differential transport equations based on the first principle is an essential step toward the characterization of porous media based on the continuum approach. For the case of water transport in non-deformable soils the Richard’s diffusion-type equation is typically used: ⭸␪ ⭸S ⫽ ⑀ ⫽ ⵜ关K共S兲ⵜ ␸ 兴 ⫽ ⵜ关K共S兲ⵜ共 z ⫺ ␺ 兲兴 ⭸t ⭸t where ⑀ is porosity, S is the saturation, ␪(⫽ ⑀S) is water content, K is the hydraulic conductivity, and is suction potential. In order to obtain reasonable simulations of mass and species transport through integration of this equation for given boundary and initial conditions it is important to know the temporal and spatial scales involved. For example, to obtain statistically steady and space-invariant scales it is important that the pore-scale is much smaller than the porosity scale (l ⬍⬍ D) and also that the integral (macro-) scale or the sample scale is much larger than the porosity scale (L ⬎⬎ D). However, these scales, in general, are not constant and may change with saturation, flow regime, packing, etc., even for what we often treat as a non-deformable porous medium. Clearly, characterization of transport and other physical properties is necessary if modeling is to produce useful results. MRI is an ideal technique to estimate different scales in porous media. A size and a shape of a voxel can be systematically changed in order to obtain the spectrum of scales from the pore-scale heterogeneities up to macro-scale inhomogeneities and the statistically-steady distributions of porosity-scales in between. This is very important part in up-scaling procedures and also in determination of proper and relevant instrumentation size (tensiometer). A 0.27 T permanent magnet at NASA GRC and both 0.27 T permanent magnet and a 1.9 T super-conducting magnet at New Mexico Resonance facility were used for this study. A porosity distribution is obtained from the NMR signal strength from each voxel and the spinlattice relaxation time. A number of engineered “space-candidate” soils such as Isolite™, Zeoponics™, Zeopro™, Jiffy Mix™, and Profile™ were used. Some foams such as AquafoamTM and glass beads in the size range from 50 to 500 ␮m were used as well. Initial results with saturated porous samples have shown a good estimate of the average porosity consistent with the traditional porosity measurement results. A spatially-resolved X-Ray CT will be used in conjuction with the average liquid-displaced (weight) method to verify spatial and average porosity obtained by MRI. Microgravity conditions will be simulated with a thin horizontal samples.

Like-charged surfactant micelles as a geometrical probe for a study of sol-gel transitions in biopolyelectrolyte solutions V. I. Chizhik1, A. A. Khripov1, K. Nishinary2 1Physics Faculty, St. Petersburg State University, 198504, St. Petersburg, Russia 2Osaka City University, 3–3-138, Sugimoto, Sumiyoshi, Osaka, 558-8585, Japan

Fig. 1. NMR data of 1.6 wt.% gellan gum –5 wt. % SDS –water system. At present there is a quite limited number of methods to experimentally estimate a polymer aggregate radius, length and the network pore radius in biopolyelectrolyte solutions [1]. The most common methods (X-ray diffraction of polycrystalline oriented fibers, atomic force and electron microscopy, light scattering) are either destructive or yield a macroscopic information on the scale of more than about 1000 nm. In this paper we for the first time present an NMR method to experimentally determine the radius of the polymer aggregates and the network pores over the range 0.5–105 nm in biopolyelectrolyte solutions. We suggest using like-charged surfactant micelles as an NMR relaxation and diffusion probe. In our NMR PGSE experiments we used an anionic surfactant, sodium dodecyl sulfate (SDS), and an anionic polysaccharide, gellan gum, producing a physical gel upon decreasing the temperature and/or increasing the ionic strength of the solution [1]. We have worked out an experimental technique of the preparation of transparent thermoreversible gels consisting of gellan up to 5% wt., SDS up to 7% wt. and water. We showed with the use of NMR, DSC, rheology and circular dichroism methods that the phase diagram of the gellan-SDS-water gels is nearly resemble one of the gellan gels containing the corresponding amount of NaCl instead of SDS. The results of the NMR investigation of the systems are partly presented in Fig. 1. Briefly commenting the data it may be said that the water self-diffusion coefficent is insensitive to the melting of the gellan network, water proton T2 gives an evidence of the gellan helix-coil transition, the SDS micelle coefficient reflects the geometrical changes of the network, namely the pore size decrease with increasing the temperature (temperature-independent plato). The observed plato is similar to the classic picture for a hydrocarbon self-diffusion in zeolites.

References [1] Nishinary KPhysical chemistry of gellan gum. Progr Colloid Polym Sc1141999

Predictions of pulsed field gradient NMR echo decays for molecules diffusing in various restrictive geometries. Simulation of the diffusion propagator based on the finite element method Håkan Hagsla¨tt, Bengt Jo¨nsson, Magnus Nyde´n, Olle So¨derman Department of Applied Surface Chemistry, Chalmers University of Technology, SE-412 96 Go¨teborg, Sweden Biophysical Chemistry, Center for Chemistry, and Chemical Engineering, P.O.Box 124SE-221

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00 Lund, Sweden Physical Chemistry 1, Center for Chemistry and Chemical Engineering, P.O.Box 124SE-221 00 Lund, Sweden Pulsed field gradient NMR diffusometry is a promising tool for investigating structures of porous material through imaging of the dynamic displacements of molecules in the porous system. A problem with this approach is the lack of a theoretical description of echo-decays in anything but very idealized pore geometries. We present here an approach based on calculating the appropriate diffusion propagator by means of finite element calculations. The suggested method is quite general, and can be applied to arbitrary porous systems. In this contribution we show results from a number of different cases including diffusion in confined geometries and in systems that are spatially inhomogeneous with respect to concentration.

Nanoscopically confined polymers as model systems for the study of segmental order and dynamics by solid-state NMR Kay Saalwa¨chter Institut fu¨r Makromolekulare Chemie, Universita¨t Freiburg, Stefan-Meier-Str. 31, D-79104 Freiburg, Germany Polymers residing in the nano-sized pores of their inclusion complexes with low molecular weight organic compounds such as urea, perhydrotriphenylene, or cyclodextrin, represent an interesting class of materials which exhibit a perfect, crystal-induced unidirectional ordering of the polymer chain [1]. Such compounds open up the possibility to study local dynamics of the isolated polymer chain without the complications arising from cooperative motions, which would usually dominate the relaxation properties of the chains in the bulk. We present solid-state NMR investigations of local segmental fluctuations and order in such a system. In particular, novel multiple-quantum magic-angle spinning (MAS) techniques [2,3], which do not require isotopic labeling, are well-suited to study local polymer dynamics very selectively [4]. Since in MAS spectra, the separation of signals from the host

and the polymer is straightforward, it is possible to measure residual homonuclear (1H-1H) and heteronuclear (1H-13C) dipolar couplings associated with the polymer. We report results on the theoretical derivation of the behavior of the 3-proton spin system of a single methyl group under a double-quantum recoupling sequence [5], and illustrate the use of the result for measurements of residual dipolar couplings of poly(dimethylsiloxane) in its inclusion compound with ␥-cyclodextrin [6]. It is shown that methyl groups are well suited local dynamic probes on account of their favorable relaxation properties and the possible isolation of intra-methyl interactions from perturbing remote couplings, which is accomplished by fast MAS. Our results indicate that the chains perform fast rotational motions about the polymer backbone, with very little contributions from off-axis librations [7]. It is possible to extract a dynamic order parameter, which, as defined relative to the backbone axis, is close to one. The interaction of the polymer chain with the host is found to be weak, but the mere presence of a measurable guest-host contact can be used to estimate an upper limit for the translational diffusion coefficient of the chain in the pore.

References [1] Tonelli AE. Polymer International 1997;43:295–309. [2] Feike M. J Magn Reson A 1996;122:214 –21. [3] Saalwc¨hter K, Graf R, Spiesss H.-W. J Magn Reson 2001;148:398 – 416. [4] Graf R, Heuer A, Spiess HW. Phys Rev Lett 1998;80:5738 – 41. [5] Saalwa¨chter K. Chem Phys Lett 2002;362:331– 40. [6] Okumura H, Kawaguchi Y, Harada A. Macromolecules 2001;34:6338 – 43. [7] Saalwa¨chter K. Macromol Rapid Commun 2002;23:286 –91.

Corresponding author. [email protected]