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Phase behavior for the poly(dimethylsiloxane) in supercritical fluid solvents
Journal of Industrial and Engineering Chemistry 19 (2013) 665–669
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Phase behavior for the poly(dimethylsiloxane) in supercritical fluid solvents Hun-Soo Byun * School of Biotechnology and Chemical Engineering, Chonnam National University, Yeosu, Jeonnam 550-749, South Korea
A R T I C L E I N F O
Article history: Received 3 July 2012 Accepted 7 October 2012 Available online 13 October 2012 Keywords: Poly(dimethylsiloxane) Supercritical solvents Phase behavior LCST
A B S T R A C T
In this work, cloud-point and bubble-point phase behavior data are reported for the poly(dimethylsiloxane) [PDMSA] in supercritical carbon dioxide, propane, propylene, butane, 1-butene and dimethyl ether (DME). The static-type method, using a variable-volume view cell, was employed to obtain the experimental data at the temperature range for (315.2–454.9) K and pressure up to 55.52 MPa. PDMS (Mw = 38,900) + C4 cloud-point curves are 10 MPa lower than the PDMS + C3 curves at constant temperature of 423 K. Cloud-point curves for the PDMS + solvents system show the lower critical solution temperature (LCST) region. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Poly(dimethylsiloxane) [PDMS] consists of fully methylated linear siloxane polymers containing repeating units of the formula, (CH3)2SiO, with trimethylsiloxy end-blocking units of the formula (CH3)3SiO–. In general, PDMS is considered to be inert, nontoxic and nonflammable. PDMS molecules have quite flexible polymer backbones due to their siloxane linkage, which can be used to introduce branches or crosslinks in the polymer chain. PDMS is used mainly for a variety of applications such as release agents, biomedical devices, form control agents, lubricants and dielectric encapsulation [1,2]. Knowledge of phase behavior of high pressure for the binary mixture of polymers in supercritical fluid (SCF) solvents is required for practical purpose in chemical separation technology, as well as related industries and polymerization processes [3,4]. Recently, we have demonstrated that it is possible to dissolve poly(acrylate) and poly(methacrylate) in supercritical fluid solvents over a wide range of temperatures at high pressure [5,6]. Also, Chalykh and Avdeyev [7] have reported the phase equilibrium of binary mixture for the polyethylene + PDMS system. Huglin and Idris [8] studied the miscibility of oligomeric PDMS with long-chain unbranched alkanes. Experimental phase behavior data for the different PDMS concentration in CO2 were reported by Bayraktar and Kiran [9]. The goal of this work is to determine the phase behavior of binary system at high pressure for the PDMS + solvents mixture. So, the data are obtained on the phase behavior of the PDMS [Mw = 38,900] in supercritical CO2 as well as on binary cloud-point
* Tel.: +82 61 659 3296; fax: +82 61 653 3659. E-mail addresses: [email protected], [email protected].
and bubble-point curves for PDMS in supercritical CO2, propane, propylene, butane, 1-butene and dimethyl ether (DME). These data shows the effect of solvent polarity on the location of cloud-point curves. 2. Experimental 2.1. Materials Poly(dimethylsiloxane) [PDMSA] (Mw = 38,900, Mw/Mn = 2.84; Mw = 90,200, Mw/Mn = 1.96; Mw = 170,300, Mw/Mn = 1.75; Tg = 150 K; CAS RN 63148-62-9) used in this work was obtained from Scientific Polymer Products, Inc. (USA), and used without further purification. The structural formula of PDMS is given in Fig. 1. CO2 (mass fraction purity >0.998) was obtained from Daesung Industrial Gases Co., propane (mass fraction purity >0.980) from LG Gas (E1), and propylene (mass fraction purity >0.996), butane (mass fraction purity >0.970), 1-butene (mass fraction purity >0.995) and dimethyl ether (DME) (mass fraction purity >0.995) from Yeochun NCC Co. (Korea). 2.2. Apparatus and procedure The measurements of cloud-point and bubble-point curves are carried out by using variable-volume view cell, which has been described in detail elsewhere [10]. We are expected to obtain the phase behavior for polymer + supercritical solvents mixture using the high-pressure experimental apparatus [11]. The pressure inside cell is measured with a Heise gauge (Dresser Ind., USA, model CM-108952, 0 345.0 MPa, accurate to within 0.35 MPa) and high-pressure generator (HIP Inc., USA, model 37-5.75-60). The temperature inside cell is measured by using a platinum-resistance
1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2012.10.003
H.-S. Byun / Journal of Industrial and Engineering Chemistry 19 (2013) 665–669
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Fig. 1. Structural formula of poly(dimethylsilosane).
thermometer (Thermometrics Corp., Class A, USA) connected to a digital multi-meter (Yokogawa, Japan, model 7563, accurate to within 0.005%). The uncertainty of system temperature is typically maintained to within 0.2 K below 473 K. The cell inside is viewed on a video monitor using a camera coupled to a borescope (Olympus Corp., Japan, model R100-038-000-50) placed against the outside of the sapphire window. Polymer is loaded into the cell to within 0.001 g and then the cell is purged with nitrogen followed by supercritical fluid solvents to ensure that all of the organic matters are removed. Supercritical solvents are transferred into the cell gravimetrically to within 0.003 g by using a high-pressure bomb. The polymer + solvent mixture in the cell is heated to the desired temperature, and pressurized until a single phase is achieved. The binary mixtures are maintained in the one-phase region at the designed temperature for at least 30–40 min, so that the cell can reach thermal equilibrium. The pressure slowly decreased until the solution becomes cloudy. The cloud-point pressure is defined as the point at which the mixture becomes so opaque that it is no longer possible to see the stir bar in the solution. After a cloud-point is obtained, the solution is recompressed into a single phase, and the process are repeated. Cloud-points and bubble-points, which are measured for the polymer solutions at a fixed PDMS concentration of 6.3 1.5 wt%, are repeated at least twice at each temperature, and uncertainty within 0.55 MPa and 0.3 K. 3. Experimental result and discussion Table 1 shows the list of the critical temperature (Tc), critical pressure (pc), critical density (rc), polarizability (a), dipole moment (m), and quadrupole moment (Q) of each solvent and cosolvent used in this study [12–16]. C3 (propane and propylene) hydrocarbons have similarity in critical properties and polarizabilities. In addition, a double bond within C3- and C4-hydrocarbons generates a significant quadrupole moments that favor interaction with polar dimethylsiloxane groups in the polymer. Hence, quadrupole interactions, which are essentially independent of dispersion interactions, can be evaluated by comparing cloudpoint curves from each pair of alkane and alkene solvents. DME has a significant dipole moment that allows the effect of dipole interactions to be compared with that of quadrupole interactions found with alkenes and CO2.
Table 1 Critical temperatures, critical pressures, critical densities, polarizabilities, dipole moments, and quadrupole moments of solvents used in this study [12–16]. Solvents CO2 Propane Propylene Butane 1-Butene Dimethyl nether
Tc (K) 304.3 342.9 365.1 425.3 419.6 400.0
pc (MPa)
rc
7.38 4.25 4.62 3.80 3.97 5.30
469 217 236 228 234 258
(kg m
3
)
a 1030
m 1030
(m3)
(C m)
Q 1040 (C m2)
2.65 6.29 6.26 8.14 8.24 5.22
0.00 0.27 1.23 0.00 1.13 4.34
-14.34 4.00 8.34 0.00 8.34 4.00
Fig. 2. Cloud-point curves for the poly(dimethylsiloxane) [PDMSA: Mw = 38,900] in supercritical CO2, dimethyl ether (DME), propane, propylene, butane and 1-butene.
Table 2 Experimental data of cloud-point for the poly(dimethylsiloxane) [PDMS] + CO2 system. T (K)
P (MPa)
Transition
5.0 wt% PDMS (Mw = 38,900) + CO2 315.2 33.13 335.0 34.14 353.3 37.07 374.0 40.86 393.7 43.97 414.2 47.41 433.2 49.14 452.6 51.38
CP CP CP CP CP CP CP CP
4.9 wt% PDMS (Mw = 90,200) + CO2 333.7 39.14 353.3 40.86 374.1 44.48 393.6 47.59 413.3 50.52 432.4 52.41 453.8 54.83
CP CP CP CP CP CP CP
5.5 wt% PDMS (Mw = 170,300) + CO2 334.5 40.52 354.2 42.24 373.0 45.00 391.9 47.76 413.9 50.86 434.7 53.28 454.3 55.52
CP CP CP CP CP CP CP
Fig. 2 shows cloud-point curves of binary mixture for the PDMSA [Mw = 38,900] containing supercritical CO2, propane, propylene, butane, 1-butene and dimethyl ether (DME) obtained in this work. The cloud-point behavior for PDMSA + CO2, +propane, +propylene, +butane, +1-butene, and +DME mixture exhibits lower critical solution temperature (LCST) type [17,18] curves with a positive slope. The phase behavior for the PDMSA + solvents systems shows at temperature ranging of (315.2–453.6) K and pressure range of (0.52–51.38) MPa. As shown in Table 1, due to no dipole moment and nonpolar in CO2, the phase behavior for the PDMSA (Mw = 38,900) + CO2 system shows higher pressure than other systems. Fig. 3 and Table 2 show the cloud-point curves for the PDMSA [Mw = 38,900, 90,200 and 170,300] in supercritical CO2 obtained in this work. The pressure difference according to phase behavior for the PDMSA + CO2 mixture is due to weight-average molecular weight (Mw). The cloud-point curves for PDMSA + CO2 system exhibits LCST-type curves with a positive slope at
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Table 4 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + propane system. T (K)
Fig. 3. Cloud-point curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical CO2.
Table 3 Cloud-point and bubble-point data for the poly(dimethylsiloxane) [PDMS] + dimethyl ether (DME) system. T (K)
P (MPa)
Transition
5.2 wt% PDMS (Mw = 38,900) + DME 334.4 1.21 353.2 2.24 372.4 2.76 393.3 4.14 413.9 7.41 433.4 10.00 452.5 12.41
BP BP BP CP CP CP CP
5.6 wt% PDMS (Mw = 90,200) + DME 334.1 1.21 354.9 2.07 372.8 3.10 394.2 4.66 413.2 7.76 432.9 10.52 453.0 12.59
BP BP BP CP CP CP CP
5.8 wt% PDMS (Mw = 170,300) + DME 333.8 1.21 352.4 1.90 372.4 3.28 393.1 4.83 413.2 8.28 434.6 11.21 454.5 13.79
BP BP BP CP CP CP CP
Fig. 4. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical dimethyl ether.
P (MPa)
Transition
5.2 wt% PDMS (Mw = 38,900) + propane 333.5 1.55 353.6 2.41 373.2 5.35 394.5 8.79 414.0 11.03 13.28 433.4 452.7 15.00
BP CP CP CP CP CP CP
5.1 wt% PDMS (Mw = 90,200) + propane 334.0 1.89 354.1 3.28 373.5 6.21 9.14 393.5 412.9 11.55 434.2 14.31 452.7 15.69
BP CP CP CP CP CP CP
4.9 wt% PDMS (Mw = 170,300) + propane 333.5 1.90 355.2 3.84 373.2 6.72 393.2 9.54 413.0 12.07 434.1 14.61 452.7 16.03
BP CP CP CP CP CP CP
temperature range of (315.2–454.3) K and pressure below 55.52 MPa. Fig. 4 and Table 3 present the cloud-point and bubble-point curves for the PDMS [Mw = 38,900, 90,200 and 170,300] + DME system obtained in this work. The solid line represents the vapor pressure for pure DME. Open reverse triangle is bubble-point data. The LCST curves for the PDMS + DME mixture show that the pressure decreases rapidly as the temperature decreases according to Mw. The upper part of LCST curves (open symbols) is fluid region, while the lower part of it is liquid + liquid region. Fig. 5 and Table 4 show the phase behavior of binary mixture for the PDMS [Mw = 38,900, 90,200 and 170,300] in supercritical propane obtained in this work. The solid line represents the vapor pressure of pure propane, and open reverse triangle is bubblepoint data. As shown in Fig. 5, all of the pressure–temperature curves exhibit positive slopes. Experimental data for the PDMS + propane system is obtained very close to the vapor pressure curve of propane. The LCST curves for the PDMS +
Fig. 5. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical propane.
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Table 5 Experimental data of cloud-point for the poly(dimethylsiloxane) [PDMS] + propylene system. T (K)
P (MPa)
Transition
6.4 wt% PDMS (Mw = 38,900) + propylene 355.7 3.97 375.5 7.24 394.7 9.66 414.6 12.41 432.1 14.48
CP CP CP CP CP
7.8 wt% PDMS (Mw = 90,200) + propylene 354.0 4.14 372.8 7.39 395.0 10.66 412.1 12.76 435.2 15.69
CP CP CP CP CP
7.3 wt% PDMS (Mw = 170,300) + propylene 355.1 4.31 374.2 7.76 393.1 10.75 412.1 13.23 434.6 15.86 442.4 16.58
CP CP CP CP CP CP
Fig. 7. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical butane.
Table 7 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + 1-butene system. T (K)
Fig. 6. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical propylene.
Table 6 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + butane system. T (K)
P (MPa)
Transition
6.7 wt% PDMS (Mw = 38,900) + butane 413.5 3.10 432.6 4.83 452.9 6.90
CP CP CP
7.3 wt% PDMS (Mw = 90,200) + butane 341.6 0.52 354.5 0.86 373.7 1.55 393.9 2.24 411.9 3.28 433.6 5.35 454.0 7.50
BP BP BP BP CP CP CP
7.4 wt% PDMS (Mw = 170,300) + butane 411.5 3.33 435.8 5.86 452.6 7.61
CP CP CP
P (MPa)
Transition
7.1 wt% PDMS (Mw = 38,900) + 1-butene 338.2 0.52 354.1 0.86 372.9 1.55 393.1 2.14 412.1 2.93 435.7 5.86 453.6 8.28
BP BP BP BP CP CP CP
7.5 wt% PDMS (Mw = 90,200) + 1-butene 341.4 0.52 354.7 0.86 374.6 1.48 391.4 2.07 413.9 3.28 433.1 5.52 454.9 7.79
BP BP BP BP CP CP CP
7.3 wt% PDMS (Mw = 170,300) + 1-butene 340.4 0.52 354.4 0.86 373.9 1.45 393.2 2.11 413.9 3.62 432.2 5.52 452.2 7.36
BP BP BP BP CP CP CP
propane system decrease at almost regular intervals in pressure according to decrease of temperature, from 452.7 K to 333.5 K. Fig. 6 and Table 5 show the LCST curves for the PDMS [Mw = 38,900, 90,200 and 170,300] in supercritical propylene. As shown in Table 1, propylene has a dipole moment and a quadrupole moment that is larger than that of propane. Therefore, propylene is expected to be a better solvent than propane for PDMS. The phase behavior for the PDMS + propylene mixture is measured at temperature range from 355.1 to 442.4 K and at pressure range from 3.97 to 16.58 MPa. The pressure difference according to Mw at constant temperature of 403.2 K shows about 0.5 1.0 MPa. Fig. 7 and Table 6 present the pressure–temperature curves for three different PDMS [Mw = 38,900, 90,200 and 170,300] + butane system obtained in this work. The phase behavior for the PDMS + butane system shows LCST-type at temperature of 411.5–454.0 K and pressure below 7.61 MPa. However, some analogous trends are observed in the PDMS + propane and
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PDMS in supercritical solvents. The phase behavior for the PDMS + solvents mixture shows the LCST-type curves. The pressure differences across phase behavior occur due to solvents quality and weight-average molecular weight of PDMS [Mw = 38,900, 90,200, 170,300]. For the PDMS + solvents system, the pressure tends to decrease according to Mw as the temperature decreases. Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant no. 2012-0008203).
Fig. 8. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical 1-butene.
References [1] [2] [3] [4] [5]
PDMS + butane cloud-point curves. The bubble-point curve for the PDMS (Mw = 90,200) + butane mixture shows up at temperature ranging of 341.6–393.9 K. Fig. 8 and Table 7 show the cloud-point and bubble-point curves for the PDMS [Mw = 38,900, 90,200 and 170,300] + 1-butene system. 1-butene has a dipole moment and a polarizability that is larger than that of butane. However, the cloud-point curve for the PDMS + 1-butene is at lower pressures than the PDMS + butane curve since the 1-butene have larger polarizabilites than the butane. The PDMS + 1-butene behavior shows cross around 433 K and 6 MPa according to the LCST curve.
[7] [8] [9] [10]
4. Conclusion
[13] [14] [15]
Six different supercritical fluids, CO2, propane, propylene, butane, 1-butene, and DME, are investigated as potential solvents for processing a PDMS. The cloud-point and bubble-point behavior to 55.52 MPa and 454.9 K are reported for binary systems with
[6]
[11] [12]
[16] [17] [18]
Alex C.M. Kuo, Polymer Data Book, Oxford University Press, Oxford, 1999, p. 411. http://en.wikipedia.org/wiki/polydimethylsiloxane. W. Bae, S. Kwon, H.S. Byun, H. Kim, Journal of Supercritical Fluids 30 (2004) 127. S.D. Yeo, E. Kiran, Macromolecules 37 (2004) 8239. Y.S. Jang, J.W. Kang, H.S. Byun, Journal of Industrial and Engineering Chemistry 16 (2010) 598. H.Y. Lee, S.D. Yoon, H.S. Byun, Journal of Chemical and Engineering Data 55 (2010) 3684. A.Y. Chalykh, N.N. Avdeyev, Polymer Science U.S.S.R 27 (1985) 2769. M.B. Huglin, I.M. Idris, European Polymer Journal 21 (1985) 9. Z. Bayraktar, E. Kiran, Journal of Applied Polymer Science 75 (2000) 1397. S.E. Kim, S.D. Yoon, K.P. Yoo, H.S. Byun, Korean Journal of Chemical Engineering 26 (2009) 199. S. Liu, H.Y. Lee, S.D. Yoon, K.P. Yoo, H.S. Byun, Industrial Chemistry & Engineering Research 48 (2009) 7821. B.E. Polling, J.M. Prausnitz, J.P. O’Connell, The Properties of Gases and Liquid, 5th ed., McGraw-Hill, New York, 2001. R.C. Benson, W.H. Flygare, Chemical Physics Letters 4 (1969) 141. G. Meyer, J.P. Toennies, Chemical Physics 52 (1980) 39. J.M. Prausniz, R.N. Lichtenthaler, E.G. de Azevedo, Molecular Thermodynamics of Fluid-Phase Equilibria, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1986. K.L. Albrecht, F.P. Stein, S.J. Han, C.J. Gregg, M. Radosz, Fluid Phase Equilibria 117 (1996) 84. C.F. Kirby, M.A. McHugh, Chemical Reviews 99 (1999) 565. M.A. McHugh, V.J. Krukonis, Supercritical Fluid Extraction: Principles and Practice, Butterworth, Boston, MA, 1994.
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Phase behavior for the poly(dimethylsiloxane) in supercritical fluid solvents Hun-Soo Byun * School of Biotechnology and Chemical Engineering, Chonnam National University, Yeosu, Jeonnam 550-749, South Korea
A R T I C L E I N F O
Article history: Received 3 July 2012 Accepted 7 October 2012 Available online 13 October 2012 Keywords: Poly(dimethylsiloxane) Supercritical solvents Phase behavior LCST
A B S T R A C T
In this work, cloud-point and bubble-point phase behavior data are reported for the poly(dimethylsiloxane) [PDMSA] in supercritical carbon dioxide, propane, propylene, butane, 1-butene and dimethyl ether (DME). The static-type method, using a variable-volume view cell, was employed to obtain the experimental data at the temperature range for (315.2–454.9) K and pressure up to 55.52 MPa. PDMS (Mw = 38,900) + C4 cloud-point curves are 10 MPa lower than the PDMS + C3 curves at constant temperature of 423 K. Cloud-point curves for the PDMS + solvents system show the lower critical solution temperature (LCST) region. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Poly(dimethylsiloxane) [PDMS] consists of fully methylated linear siloxane polymers containing repeating units of the formula, (CH3)2SiO, with trimethylsiloxy end-blocking units of the formula (CH3)3SiO–. In general, PDMS is considered to be inert, nontoxic and nonflammable. PDMS molecules have quite flexible polymer backbones due to their siloxane linkage, which can be used to introduce branches or crosslinks in the polymer chain. PDMS is used mainly for a variety of applications such as release agents, biomedical devices, form control agents, lubricants and dielectric encapsulation [1,2]. Knowledge of phase behavior of high pressure for the binary mixture of polymers in supercritical fluid (SCF) solvents is required for practical purpose in chemical separation technology, as well as related industries and polymerization processes [3,4]. Recently, we have demonstrated that it is possible to dissolve poly(acrylate) and poly(methacrylate) in supercritical fluid solvents over a wide range of temperatures at high pressure [5,6]. Also, Chalykh and Avdeyev [7] have reported the phase equilibrium of binary mixture for the polyethylene + PDMS system. Huglin and Idris [8] studied the miscibility of oligomeric PDMS with long-chain unbranched alkanes. Experimental phase behavior data for the different PDMS concentration in CO2 were reported by Bayraktar and Kiran [9]. The goal of this work is to determine the phase behavior of binary system at high pressure for the PDMS + solvents mixture. So, the data are obtained on the phase behavior of the PDMS [Mw = 38,900] in supercritical CO2 as well as on binary cloud-point
* Tel.: +82 61 659 3296; fax: +82 61 653 3659. E-mail addresses: [email protected], [email protected].
and bubble-point curves for PDMS in supercritical CO2, propane, propylene, butane, 1-butene and dimethyl ether (DME). These data shows the effect of solvent polarity on the location of cloud-point curves. 2. Experimental 2.1. Materials Poly(dimethylsiloxane) [PDMSA] (Mw = 38,900, Mw/Mn = 2.84; Mw = 90,200, Mw/Mn = 1.96; Mw = 170,300, Mw/Mn = 1.75; Tg = 150 K; CAS RN 63148-62-9) used in this work was obtained from Scientific Polymer Products, Inc. (USA), and used without further purification. The structural formula of PDMS is given in Fig. 1. CO2 (mass fraction purity >0.998) was obtained from Daesung Industrial Gases Co., propane (mass fraction purity >0.980) from LG Gas (E1), and propylene (mass fraction purity >0.996), butane (mass fraction purity >0.970), 1-butene (mass fraction purity >0.995) and dimethyl ether (DME) (mass fraction purity >0.995) from Yeochun NCC Co. (Korea). 2.2. Apparatus and procedure The measurements of cloud-point and bubble-point curves are carried out by using variable-volume view cell, which has been described in detail elsewhere [10]. We are expected to obtain the phase behavior for polymer + supercritical solvents mixture using the high-pressure experimental apparatus [11]. The pressure inside cell is measured with a Heise gauge (Dresser Ind., USA, model CM-108952, 0 345.0 MPa, accurate to within 0.35 MPa) and high-pressure generator (HIP Inc., USA, model 37-5.75-60). The temperature inside cell is measured by using a platinum-resistance
1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2012.10.003
H.-S. Byun / Journal of Industrial and Engineering Chemistry 19 (2013) 665–669
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Fig. 1. Structural formula of poly(dimethylsilosane).
thermometer (Thermometrics Corp., Class A, USA) connected to a digital multi-meter (Yokogawa, Japan, model 7563, accurate to within 0.005%). The uncertainty of system temperature is typically maintained to within 0.2 K below 473 K. The cell inside is viewed on a video monitor using a camera coupled to a borescope (Olympus Corp., Japan, model R100-038-000-50) placed against the outside of the sapphire window. Polymer is loaded into the cell to within 0.001 g and then the cell is purged with nitrogen followed by supercritical fluid solvents to ensure that all of the organic matters are removed. Supercritical solvents are transferred into the cell gravimetrically to within 0.003 g by using a high-pressure bomb. The polymer + solvent mixture in the cell is heated to the desired temperature, and pressurized until a single phase is achieved. The binary mixtures are maintained in the one-phase region at the designed temperature for at least 30–40 min, so that the cell can reach thermal equilibrium. The pressure slowly decreased until the solution becomes cloudy. The cloud-point pressure is defined as the point at which the mixture becomes so opaque that it is no longer possible to see the stir bar in the solution. After a cloud-point is obtained, the solution is recompressed into a single phase, and the process are repeated. Cloud-points and bubble-points, which are measured for the polymer solutions at a fixed PDMS concentration of 6.3 1.5 wt%, are repeated at least twice at each temperature, and uncertainty within 0.55 MPa and 0.3 K. 3. Experimental result and discussion Table 1 shows the list of the critical temperature (Tc), critical pressure (pc), critical density (rc), polarizability (a), dipole moment (m), and quadrupole moment (Q) of each solvent and cosolvent used in this study [12–16]. C3 (propane and propylene) hydrocarbons have similarity in critical properties and polarizabilities. In addition, a double bond within C3- and C4-hydrocarbons generates a significant quadrupole moments that favor interaction with polar dimethylsiloxane groups in the polymer. Hence, quadrupole interactions, which are essentially independent of dispersion interactions, can be evaluated by comparing cloudpoint curves from each pair of alkane and alkene solvents. DME has a significant dipole moment that allows the effect of dipole interactions to be compared with that of quadrupole interactions found with alkenes and CO2.
Table 1 Critical temperatures, critical pressures, critical densities, polarizabilities, dipole moments, and quadrupole moments of solvents used in this study [12–16]. Solvents CO2 Propane Propylene Butane 1-Butene Dimethyl nether
Tc (K) 304.3 342.9 365.1 425.3 419.6 400.0
pc (MPa)
rc
7.38 4.25 4.62 3.80 3.97 5.30
469 217 236 228 234 258
(kg m
3
)
a 1030
m 1030
(m3)
(C m)
Q 1040 (C m2)
2.65 6.29 6.26 8.14 8.24 5.22
0.00 0.27 1.23 0.00 1.13 4.34
-14.34 4.00 8.34 0.00 8.34 4.00
Fig. 2. Cloud-point curves for the poly(dimethylsiloxane) [PDMSA: Mw = 38,900] in supercritical CO2, dimethyl ether (DME), propane, propylene, butane and 1-butene.
Table 2 Experimental data of cloud-point for the poly(dimethylsiloxane) [PDMS] + CO2 system. T (K)
P (MPa)
Transition
5.0 wt% PDMS (Mw = 38,900) + CO2 315.2 33.13 335.0 34.14 353.3 37.07 374.0 40.86 393.7 43.97 414.2 47.41 433.2 49.14 452.6 51.38
CP CP CP CP CP CP CP CP
4.9 wt% PDMS (Mw = 90,200) + CO2 333.7 39.14 353.3 40.86 374.1 44.48 393.6 47.59 413.3 50.52 432.4 52.41 453.8 54.83
CP CP CP CP CP CP CP
5.5 wt% PDMS (Mw = 170,300) + CO2 334.5 40.52 354.2 42.24 373.0 45.00 391.9 47.76 413.9 50.86 434.7 53.28 454.3 55.52
CP CP CP CP CP CP CP
Fig. 2 shows cloud-point curves of binary mixture for the PDMSA [Mw = 38,900] containing supercritical CO2, propane, propylene, butane, 1-butene and dimethyl ether (DME) obtained in this work. The cloud-point behavior for PDMSA + CO2, +propane, +propylene, +butane, +1-butene, and +DME mixture exhibits lower critical solution temperature (LCST) type [17,18] curves with a positive slope. The phase behavior for the PDMSA + solvents systems shows at temperature ranging of (315.2–453.6) K and pressure range of (0.52–51.38) MPa. As shown in Table 1, due to no dipole moment and nonpolar in CO2, the phase behavior for the PDMSA (Mw = 38,900) + CO2 system shows higher pressure than other systems. Fig. 3 and Table 2 show the cloud-point curves for the PDMSA [Mw = 38,900, 90,200 and 170,300] in supercritical CO2 obtained in this work. The pressure difference according to phase behavior for the PDMSA + CO2 mixture is due to weight-average molecular weight (Mw). The cloud-point curves for PDMSA + CO2 system exhibits LCST-type curves with a positive slope at
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Table 4 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + propane system. T (K)
Fig. 3. Cloud-point curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical CO2.
Table 3 Cloud-point and bubble-point data for the poly(dimethylsiloxane) [PDMS] + dimethyl ether (DME) system. T (K)
P (MPa)
Transition
5.2 wt% PDMS (Mw = 38,900) + DME 334.4 1.21 353.2 2.24 372.4 2.76 393.3 4.14 413.9 7.41 433.4 10.00 452.5 12.41
BP BP BP CP CP CP CP
5.6 wt% PDMS (Mw = 90,200) + DME 334.1 1.21 354.9 2.07 372.8 3.10 394.2 4.66 413.2 7.76 432.9 10.52 453.0 12.59
BP BP BP CP CP CP CP
5.8 wt% PDMS (Mw = 170,300) + DME 333.8 1.21 352.4 1.90 372.4 3.28 393.1 4.83 413.2 8.28 434.6 11.21 454.5 13.79
BP BP BP CP CP CP CP
Fig. 4. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical dimethyl ether.
P (MPa)
Transition
5.2 wt% PDMS (Mw = 38,900) + propane 333.5 1.55 353.6 2.41 373.2 5.35 394.5 8.79 414.0 11.03 13.28 433.4 452.7 15.00
BP CP CP CP CP CP CP
5.1 wt% PDMS (Mw = 90,200) + propane 334.0 1.89 354.1 3.28 373.5 6.21 9.14 393.5 412.9 11.55 434.2 14.31 452.7 15.69
BP CP CP CP CP CP CP
4.9 wt% PDMS (Mw = 170,300) + propane 333.5 1.90 355.2 3.84 373.2 6.72 393.2 9.54 413.0 12.07 434.1 14.61 452.7 16.03
BP CP CP CP CP CP CP
temperature range of (315.2–454.3) K and pressure below 55.52 MPa. Fig. 4 and Table 3 present the cloud-point and bubble-point curves for the PDMS [Mw = 38,900, 90,200 and 170,300] + DME system obtained in this work. The solid line represents the vapor pressure for pure DME. Open reverse triangle is bubble-point data. The LCST curves for the PDMS + DME mixture show that the pressure decreases rapidly as the temperature decreases according to Mw. The upper part of LCST curves (open symbols) is fluid region, while the lower part of it is liquid + liquid region. Fig. 5 and Table 4 show the phase behavior of binary mixture for the PDMS [Mw = 38,900, 90,200 and 170,300] in supercritical propane obtained in this work. The solid line represents the vapor pressure of pure propane, and open reverse triangle is bubblepoint data. As shown in Fig. 5, all of the pressure–temperature curves exhibit positive slopes. Experimental data for the PDMS + propane system is obtained very close to the vapor pressure curve of propane. The LCST curves for the PDMS +
Fig. 5. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical propane.
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Table 5 Experimental data of cloud-point for the poly(dimethylsiloxane) [PDMS] + propylene system. T (K)
P (MPa)
Transition
6.4 wt% PDMS (Mw = 38,900) + propylene 355.7 3.97 375.5 7.24 394.7 9.66 414.6 12.41 432.1 14.48
CP CP CP CP CP
7.8 wt% PDMS (Mw = 90,200) + propylene 354.0 4.14 372.8 7.39 395.0 10.66 412.1 12.76 435.2 15.69
CP CP CP CP CP
7.3 wt% PDMS (Mw = 170,300) + propylene 355.1 4.31 374.2 7.76 393.1 10.75 412.1 13.23 434.6 15.86 442.4 16.58
CP CP CP CP CP CP
Fig. 7. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical butane.
Table 7 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + 1-butene system. T (K)
Fig. 6. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical propylene.
Table 6 Experimental data of cloud-point and bubble-point for the poly(dimethylsiloxane) [PDMS] + butane system. T (K)
P (MPa)
Transition
6.7 wt% PDMS (Mw = 38,900) + butane 413.5 3.10 432.6 4.83 452.9 6.90
CP CP CP
7.3 wt% PDMS (Mw = 90,200) + butane 341.6 0.52 354.5 0.86 373.7 1.55 393.9 2.24 411.9 3.28 433.6 5.35 454.0 7.50
BP BP BP BP CP CP CP
7.4 wt% PDMS (Mw = 170,300) + butane 411.5 3.33 435.8 5.86 452.6 7.61
CP CP CP
P (MPa)
Transition
7.1 wt% PDMS (Mw = 38,900) + 1-butene 338.2 0.52 354.1 0.86 372.9 1.55 393.1 2.14 412.1 2.93 435.7 5.86 453.6 8.28
BP BP BP BP CP CP CP
7.5 wt% PDMS (Mw = 90,200) + 1-butene 341.4 0.52 354.7 0.86 374.6 1.48 391.4 2.07 413.9 3.28 433.1 5.52 454.9 7.79
BP BP BP BP CP CP CP
7.3 wt% PDMS (Mw = 170,300) + 1-butene 340.4 0.52 354.4 0.86 373.9 1.45 393.2 2.11 413.9 3.62 432.2 5.52 452.2 7.36
BP BP BP BP CP CP CP
propane system decrease at almost regular intervals in pressure according to decrease of temperature, from 452.7 K to 333.5 K. Fig. 6 and Table 5 show the LCST curves for the PDMS [Mw = 38,900, 90,200 and 170,300] in supercritical propylene. As shown in Table 1, propylene has a dipole moment and a quadrupole moment that is larger than that of propane. Therefore, propylene is expected to be a better solvent than propane for PDMS. The phase behavior for the PDMS + propylene mixture is measured at temperature range from 355.1 to 442.4 K and at pressure range from 3.97 to 16.58 MPa. The pressure difference according to Mw at constant temperature of 403.2 K shows about 0.5 1.0 MPa. Fig. 7 and Table 6 present the pressure–temperature curves for three different PDMS [Mw = 38,900, 90,200 and 170,300] + butane system obtained in this work. The phase behavior for the PDMS + butane system shows LCST-type at temperature of 411.5–454.0 K and pressure below 7.61 MPa. However, some analogous trends are observed in the PDMS + propane and
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PDMS in supercritical solvents. The phase behavior for the PDMS + solvents mixture shows the LCST-type curves. The pressure differences across phase behavior occur due to solvents quality and weight-average molecular weight of PDMS [Mw = 38,900, 90,200, 170,300]. For the PDMS + solvents system, the pressure tends to decrease according to Mw as the temperature decreases. Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant no. 2012-0008203).
Fig. 8. Phase behavior curves for the poly(dimethylsiloxane) [PDMSA, Mw = 38,900, 90,200 and 170,300] in supercritical 1-butene.
References [1] [2] [3] [4] [5]
PDMS + butane cloud-point curves. The bubble-point curve for the PDMS (Mw = 90,200) + butane mixture shows up at temperature ranging of 341.6–393.9 K. Fig. 8 and Table 7 show the cloud-point and bubble-point curves for the PDMS [Mw = 38,900, 90,200 and 170,300] + 1-butene system. 1-butene has a dipole moment and a polarizability that is larger than that of butane. However, the cloud-point curve for the PDMS + 1-butene is at lower pressures than the PDMS + butane curve since the 1-butene have larger polarizabilites than the butane. The PDMS + 1-butene behavior shows cross around 433 K and 6 MPa according to the LCST curve.
[7] [8] [9] [10]
4. Conclusion
[13] [14] [15]
Six different supercritical fluids, CO2, propane, propylene, butane, 1-butene, and DME, are investigated as potential solvents for processing a PDMS. The cloud-point and bubble-point behavior to 55.52 MPa and 454.9 K are reported for binary systems with
[6]
[11] [12]
[16] [17] [18]
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