Binary solvents preferential sorption

In binary solvents, preferential sorption of components of the solvent on the polymer chain constitutes an additional factor affecting the microenvironment of the polymer. For PHEMA, which was studied intensively in a series of binary solvents, one component of the solvent mixture is preferentially sorbed by the polymer coil. Figure 4 shows the dependence of the limiting viscosity number [nl and the preferential sorption coefficient y (at y < 0 water is preferentially sorbed, at y > 0... 

The total sorption can be determined by die total content of the mixed solvent in die swollen skin or in the swollen elastic network (these results). The dependencies of Qv on (p (Figures 6.2.5-6.2.8) reveal the inlluenee of liquid phase composition on die total sorption. The total sorption of the binary solvent by polymer can also be measured by the value of the volume fraction of polymer in the swollen gel because the value of 1)3 is unequally related to the volume fraction of the absorbed liquid, 1)3 = l-(t), +1>2). At the fixed total sorption (Qv or 1)3 = const) die preferential sorption, s, can be found from the following equation ... 

As expected,preferential sorption was observed, with the essential distinction of molar volumes Vi and Vj of components of the mixed solvent (hexane-DBP, DOS-DEP). For swelling of the crosslinked elastomer SCN-26 in the mixture of components, having similar molar volumes Vj and Vj (e.g., amyl acetate-dimethyl phthalate) the preferential sorption of components of SL is practically absent. Influence of Vj and V2 and the influence of double interaction parameters on the sorption of binary liquids by crosslinked elastomers was examined by the method of mathematical experiment. Therewith the set of equations describing swelling of crosslinked elastomers in binary mixture, similar to the equations obtained by Bristow from the Flory-Rehner theory and from the work of Schulz and Flory, were used ... 

With preferential sorption of one component of the binary solvent on the polymer coil, an increase or decrease of the polarity of the polymer microenvironment occurs depending on whether the more polar (water) or less polar (organic solvent) component is sorbed. Preferential sorption occurs for PHEMA in 1-propanol/water, dioxane/water, and acetone/water mixtures (Figures 4 and 5). When the more polar component (water) is preferentially sorbed from mixtures in which its concentration is low, then the apolar contribution of the polymer may be compensated to that extent, since the polarity of the polymer chain microenvironment is even higher than the bulk solvent polarity. As a result, the curves of the dependence of Ej for the polymer on the solvent composition intersect the same dependence for mixed solvents. This phenomenon was observed for PHEMA in 1-propanol/water (Figure 4), dioxane/water, and acetone/water (Figure 5). Preferential sorption is also indicated by the results for PMMA and PBMA in methanol/toluene mixtures. Preferential sorption was previously found in this system by dialysis equilibria. ... 

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