Partial molar excess free enthalpies of n‐alkenes in apiezon M and alkanes in squalane and polydimethylsiloxane, and the solution theories of prigogine and flory: An investigation by gas chromatography

Abstract

Partial molar excess free enthalpies (or excess chemical potentials) at infinite dilution were obtained over a large temperature range by gas chromatography. Data on n‐alkenes in Apiezon M are interpreted by the Prigogine–Patterson theory; data on normal and branched alkanes in squalane and polydimethylsiloxane (PDMS) are discussed in terms of the Prigogine–Patterson theory and the solution theory of Flory, Orwoll, and Vrij. For the alkane–PDMS systems heats of dilution and partial excess heat capacity data are given. The aim of this work is to get some insight in the applicability of these solution theories to mixtures of fluids, the properties of which may slightly violate the basic assumptions of these theories. It is shown that orientational order in and a large cross‐sectional chain diameter of the polymer solvent do not affect their applicability to the partical molar excess free enthalpies of apolar mixtures, whereas large dissimilarities between the force fields around the segments of the mixture components and/or dissimilar chain flexibilities detract from the applicability of these theories (alkanes in PDMS). Special attention has been paid to the effects of dissimilar size and shape of the segments of the mixture compounds on the magnitude of the interchange interaction parameter. It is shown that the multiple‐connected segment model after Lichtenthaler et al. does not warrant a reliable combinatorial contribution. Comparison of the interaction parameters obtained for n‐alkanes in n‐alkanes, Apiezon, squalane, and polyisobutylene and for branched alkanes in squalane reveals that the magnitude of this parameter is affected by small end‐effects due to the relative weakness of methyl‐methylene interactions.

Gas−Liquid Chromatographic Study of the Solution Thermodynamics of Hydroxylic Derivatives in Selected Polymeric Liquids

“…Poly(dimethylsiloxane)s (PDMS) have been the subject of many studies. − Although these stationary phases can be used at higher temperatures, most PDMS studies have been conducted at temperature ranges below this study. A wide temperature range measurement for PDMS was made by Galin .…”

Thermodynamics of poly(dimethylsiloxane)-alkane systems by gas-liquid chromatography

“…In 7X"(0> = k/T+q (7) Then, from eq 4 and 5 we have A#XE" = Rk (8) ASxe" = -Rq (9) At level (b), the temperature dependence of In 7X"<0) can be shown to have the form In 7X"(0) -c In T+d/T+e (10) from which we obtain ACV" = -Be (11) A#XE" =Rd-RTc (12) ASxe" = -R(c + e) -Rc In T (13) The constants k and q or c, d, and e were obtained by a robust regression analysis of the data sets with eq 7 and 10. For all the solute-solvent pairs, this was accomplished with the method of iteratively reweighted least squares.27…”

Thermodynamics of poly[methyl(trifluoropropyl)siloxane]-alkane systems by gas-liquid chromatography

“…This value is based upon the temperature variation of the partial specific volume of PMTFPS in solution.24 Assuming that all noncombinatorial contributions to the excess Gibbs energy are accounted for by the regular solution theory, the interaction parameter is related to the solubility parameters of the two components by25 = 11? ( -2)2/( ) (5) Rearranging eq 5, one obtains 62/(RT) -X/V1L°= 2 1 2/( ) -622/(RT) (6) According to eq 6, a plot of the left-hand side of the equation versus the solubility parameter of the solute, should yield a straight line with a slope of 2b2j(RT) and an intercept of -22/ (RT), so that the polymer solubility parameter, o2, may be evaluated. In order to obtain the 2 values at several different temperatures (see Results and Discussion), the solubility parameters of the solutes at the respective temperatures Me required.…”