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SANS study of micelle formation in aqueous mixed solutions of sodium and magnesium dodecylsulfates. Part I
Physica B 276}278 (2000) 339}340
SANS study of micelle formation in aqueous mixed solutions of sodium and magnesium dodecylsulfates. Part I M. Avdeev *, V. Garamus, L. Rosta , I. Smirnova, N. Smirnova Neutron Optics Department, RISSP, KFKI P.O. Box 49, Budapest H-1525, Hungary FLNP, JINR, 141980 Dubna, Moscow region, Russia GKSS, D-21502, Geesthacht, Germany St. Petersburg State University, 198904 St. Petersburg, Russia
Abstract Mixtures of two anionic surfactants } sodium and magnesium dodecyl sulfates } in heavy water were studied by small-angle neutron scattering (SANS) at various values of the total concentration of the surfactants. Experimental conditions and data treatment are presented. Results and concluding remarks can be found in Part II further in these proceedings. 2000 Elsevier Science B.V. All rights reserved. Keywords: Small-angle neutron scattering; Surfactants; Micelles
1. Introduction Signi"cant di!erence in the behavior of the mixed systems of surfactants in comparison with their individual solutions [1] explains a great interest to these systems and their wide use in various areas of industry, households and others [2]. Small-angle neutron scattering (SANS) is a powerful technique to study the structural features of the micellar systems [3], in particular, in mixed solutions. In the present study SANS is applied to the mixtures of two anionic surfactants } sodium and magnesium dodecyl sulfates. The change of the parameters of micelles as a function of the relative concentration of the surfactants was followed at di!erent values of the total concentration with the aim to determine the role of the counterion nature in the mixed micelle formation. This information is of interest for the modern molecular theory of mixed micelles [4]. 2. Experimental Commercial sodium dodecylsulfate, SDS (Fluka, purity '99%) was used. Magnesium dodecylsulfate * Corresponding author. Fax: #36-1-395-9162. E-mail address: [email protected] (M. Avdeev)
Mg(DS) was obtained at Chemistry Department of St. Petersburg University (purity '98%). Mixed solutions in 98% purity D O with various relative concentration of surfactants (x) were studied at three "xed values of the total surfactant concentration (c) 0.05, 0.1 and 0.3 M dm\. The relative concentration is given with respect to DS relating to SDS-Mg DS mixture, x" [Mg DS]/c. The temperature of solutions was 353C. The data on the critical micelle concentration (CMC) at ¹"253C determined by viscosity are presented in Fig. 1. We found no signi"cant di!erence in CMC at these two temperatures for SDS and Mg(DS) individual solutions and, then, used the dependence in Fig. 1 de"ning CMC for some points by linear interpolation. SANS experiments were carried out on the YuMO time-of-#ight di!ractometer [5] at the IBR-2 pulsed reactor at the Frank Laboratory of Neutron Physics, Dubna, Russia, and the small-angle di!ractometer at the Research Institute for Solid State Physics and Optics at the Budapest Neutron Centre (BNC), Hungary. On YuMO measurements at c"0.05 and 0.2 M dm\ were made using the white-beam with a limited wavelength range 0.6}5 As and one sample-position distance 10.2 m giving a q-range 0.009}0.25 As \. The cross-section was calibrated to the absolute scale using a vanadium standard [5]. The resolution function was taken into account
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 5 4 3 - 4
340
M. Avdeev et al. / Physica B 276}278 (2000) 339}340
Fig. 1. Dependence of CMC on the relative concentration x. ¹"253C.
[5,6]. Measurements at BNC with c"0.1 M dm\ were made at "xed wavelength 3.6 As (resolution 13%) and two sample-detector distances 5.5 and 1.3 m to cover a qrange 0.02}0.5 As \. The absolute calibration was made using H O with the inelasticity factor from Ref. [7]. The resolution function was calculated according to Ref. [8]. The systematic errors were not taken into account at both instruments. Details of the model used for the data treatment are described in the previous papers [9}11,6]. Like in Ref. [10] we tried the spherical and ellipsoidal shape models for the form-factor and used the rescaled mean spherical approximation (RMSA) model [12] for the structural factor. Free parameters were the mean aggregation number N , the e!ective fractional charge a, the ratio of ellipsoid axes f and the residual incoherent background B. The extent of water penetration b was "xed to the unit value which is true for the studied concentrations [10]. One example of a typical scattering curve together with the "ts is presented in Fig. 2. One can see that the model with the ellipsoidal form-factor gives better "ts. This model was used to obtain quantitative results which
Fig. 2. Scattering curve and "ts for x"0.5, c"0.1 M dm\.
are presented in the next part of this work further in these proceedings.
References [1] M. Rosen, D. Murphy, J. Colloid Interface Sci. 110 (1986) 224. [2] J.F. Scamehorn, Phenomenon in mixed surfactant systems, ACS Symposium Series 311, American Chemical Society, Washington, DC, 1986. [3] J.B. Hayter, J. Penfold, J. Colloid Polym. Sci. 261 (1983) 1072. [4] A. Shiloach, D. Blankschtein, Langmuir 14 (1998) 1618. [5] Yu.M. Ostanevich, Macromol. Chem. Macromol. Symp. 15 (1988) 91. [6] L.A. Bulavin et al., Colloid J. RAS 59 (1997) 30. [7] B. Jacrot, Rep. Prog. Phys. 39 (1976) 911. [8] J. Skov Pedersen et al., J. Appl. Crystallogr. 23 (1990) 321. [9] S. Borbely et al., Colloid Polym. Sci. 271 (1993) 786. [10] S. Borbely, et al., Physica B 213 and 214 (1995) 600. [11] V.M. Garamus, Langmuir 13 (1997) 6388. [12] J.B. Hayter, J. Penfold, J. Mol. Phys. 42 (1981) 109.
SANS study of micelle formation in aqueous mixed solutions of sodium and magnesium dodecylsulfates. Part I M. Avdeev *, V. Garamus, L. Rosta , I. Smirnova, N. Smirnova Neutron Optics Department, RISSP, KFKI P.O. Box 49, Budapest H-1525, Hungary FLNP, JINR, 141980 Dubna, Moscow region, Russia GKSS, D-21502, Geesthacht, Germany St. Petersburg State University, 198904 St. Petersburg, Russia
Abstract Mixtures of two anionic surfactants } sodium and magnesium dodecyl sulfates } in heavy water were studied by small-angle neutron scattering (SANS) at various values of the total concentration of the surfactants. Experimental conditions and data treatment are presented. Results and concluding remarks can be found in Part II further in these proceedings. 2000 Elsevier Science B.V. All rights reserved. Keywords: Small-angle neutron scattering; Surfactants; Micelles
1. Introduction Signi"cant di!erence in the behavior of the mixed systems of surfactants in comparison with their individual solutions [1] explains a great interest to these systems and their wide use in various areas of industry, households and others [2]. Small-angle neutron scattering (SANS) is a powerful technique to study the structural features of the micellar systems [3], in particular, in mixed solutions. In the present study SANS is applied to the mixtures of two anionic surfactants } sodium and magnesium dodecyl sulfates. The change of the parameters of micelles as a function of the relative concentration of the surfactants was followed at di!erent values of the total concentration with the aim to determine the role of the counterion nature in the mixed micelle formation. This information is of interest for the modern molecular theory of mixed micelles [4]. 2. Experimental Commercial sodium dodecylsulfate, SDS (Fluka, purity '99%) was used. Magnesium dodecylsulfate * Corresponding author. Fax: #36-1-395-9162. E-mail address: [email protected] (M. Avdeev)
Mg(DS) was obtained at Chemistry Department of St. Petersburg University (purity '98%). Mixed solutions in 98% purity D O with various relative concentration of surfactants (x) were studied at three "xed values of the total surfactant concentration (c) 0.05, 0.1 and 0.3 M dm\. The relative concentration is given with respect to DS relating to SDS-Mg DS mixture, x" [Mg DS]/c. The temperature of solutions was 353C. The data on the critical micelle concentration (CMC) at ¹"253C determined by viscosity are presented in Fig. 1. We found no signi"cant di!erence in CMC at these two temperatures for SDS and Mg(DS) individual solutions and, then, used the dependence in Fig. 1 de"ning CMC for some points by linear interpolation. SANS experiments were carried out on the YuMO time-of-#ight di!ractometer [5] at the IBR-2 pulsed reactor at the Frank Laboratory of Neutron Physics, Dubna, Russia, and the small-angle di!ractometer at the Research Institute for Solid State Physics and Optics at the Budapest Neutron Centre (BNC), Hungary. On YuMO measurements at c"0.05 and 0.2 M dm\ were made using the white-beam with a limited wavelength range 0.6}5 As and one sample-position distance 10.2 m giving a q-range 0.009}0.25 As \. The cross-section was calibrated to the absolute scale using a vanadium standard [5]. The resolution function was taken into account
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 5 4 3 - 4
340
M. Avdeev et al. / Physica B 276}278 (2000) 339}340
Fig. 1. Dependence of CMC on the relative concentration x. ¹"253C.
[5,6]. Measurements at BNC with c"0.1 M dm\ were made at "xed wavelength 3.6 As (resolution 13%) and two sample-detector distances 5.5 and 1.3 m to cover a qrange 0.02}0.5 As \. The absolute calibration was made using H O with the inelasticity factor from Ref. [7]. The resolution function was calculated according to Ref. [8]. The systematic errors were not taken into account at both instruments. Details of the model used for the data treatment are described in the previous papers [9}11,6]. Like in Ref. [10] we tried the spherical and ellipsoidal shape models for the form-factor and used the rescaled mean spherical approximation (RMSA) model [12] for the structural factor. Free parameters were the mean aggregation number N , the e!ective fractional charge a, the ratio of ellipsoid axes f and the residual incoherent background B. The extent of water penetration b was "xed to the unit value which is true for the studied concentrations [10]. One example of a typical scattering curve together with the "ts is presented in Fig. 2. One can see that the model with the ellipsoidal form-factor gives better "ts. This model was used to obtain quantitative results which
Fig. 2. Scattering curve and "ts for x"0.5, c"0.1 M dm\.
are presented in the next part of this work further in these proceedings.
References [1] M. Rosen, D. Murphy, J. Colloid Interface Sci. 110 (1986) 224. [2] J.F. Scamehorn, Phenomenon in mixed surfactant systems, ACS Symposium Series 311, American Chemical Society, Washington, DC, 1986. [3] J.B. Hayter, J. Penfold, J. Colloid Polym. Sci. 261 (1983) 1072. [4] A. Shiloach, D. Blankschtein, Langmuir 14 (1998) 1618. [5] Yu.M. Ostanevich, Macromol. Chem. Macromol. Symp. 15 (1988) 91. [6] L.A. Bulavin et al., Colloid J. RAS 59 (1997) 30. [7] B. Jacrot, Rep. Prog. Phys. 39 (1976) 911. [8] J. Skov Pedersen et al., J. Appl. Crystallogr. 23 (1990) 321. [9] S. Borbely et al., Colloid Polym. Sci. 271 (1993) 786. [10] S. Borbely, et al., Physica B 213 and 214 (1995) 600. [11] V.M. Garamus, Langmuir 13 (1997) 6388. [12] J.B. Hayter, J. Penfold, J. Mol. Phys. 42 (1981) 109.