Modeling the Effects of Cosolvent-Modified Supercritical Fluids on Polymers with a Lattice Fluid Equation of State

Abstract

A single Sanchez−Lacombe lattice fluid equation of state is used to model both phases for a polymer−supercritical fluid−cosolvent system. This method represents well over a wide pressure range both volumetric and phase equilibrium properties for a cross-linked poly(dimethyl siloxane) phase in contact with CO2 modified by a number of cosolvents. A single adjustable binary interaction parameter, obtained from swelling data of the polymer, is used to correlate both polymer dilation and solvent sorption.

Determination of thermodynamic properties by supercritical fluid chromatography

“…Xu et al [167] and Edwards et al [181] also employed the Martire-Boehm [66] model that is similar to but mathematically simpler than the S-L model. On the whole, the performance of all these models in fitting the experimental data is comparable, and it is also truly remarkable, particularly in the systems containing polar cosolvents [120,164].…”

“…In thermodynamic measurements employing commercial open tubular columns, the crosslink density in the siloxane polymer film on the column wall is often unknown but it is probably low enough to be negligible [23]. An indirect support for this opinion comes from the work of West et al [164] who used the Sanchez-Lacombe (S-L) mean-field lattice fluid model (Section 4.1.4) to explain the very small difference between swelling of lightly crosslinked [23] and non-crosslinked (liquid) [152] PDMS (see Fig. 6).…”

“…In order to correlate their experimental results or to calculate some auxiliary properties, many authors cited in Section 2 of this review used the S-L model [23,120,154,164,165,183,184], the P-V model [72,73,79], or both [152,181]. Xu et al [167] and Edwards et al [181] also employed the Martire-Boehm [66] model that is similar to but mathematically simpler than the S-L model.…”

“…Effect of crosslinks on equilibrium swelling of PDMS by scCO 2 at 35 • C calculated[164] from the Sanchez-Lacombe EOS. Top curve, liquid PDMS; bottom curve, lightly cross-linked PDMS.…”

Unified Chromatography: What Is It?

“…More recently, Eckert et al (16) studied the effect of various modifiers, viz., methanol, acetone, and isopropanol, on the swelling of poly(dimethylsiloxane) caused by the absorption of modifier by the polymer over a range of temperatures and pressures. Eckert et al (17) used the Sanchez-Lacombe lattice fluid model, the same basic idea used by Martire for his Unified Theory of Chromatography, to model the swelling, absorption, and isothermal phase behavior for the modifiers. Again, the lattice fluid models are complex, but their ability to describe such complex systems involving a solute, supercritical C0 2 and a polar liquid modifier, all in equilibrium with a polymeric stationary liquid phase, is quite remarkable and bodes well for our ability to develop a truly comprehensive theory for a hypothetical unified chromatography.…”