6533b828fe1ef96bd1287881

RESEARCH PRODUCT

Solvent quality as reflected in concentration- and temperature-dependent Flory-Huggins interaction parameters

subject

description

Flory-Huggins interaction parameters (χ) between poly(dimethylsiloxane) (weight-average molecular weight = 152 kg/mol) and various solvents (methyl ethyl ketone, toluene and n-octane) were determined as a function of composition and temperature with vapor-pressure measurements. These data, complemented by independent information for dilute and very concentrated solutions, serve as the basis for a discussion of solvent quality via different theoretical relations. Regardless of polymer concentration, the χ values fall from methyl ethyl ketone via toluene to n-octane, the ketone being the worst solvent and the hydrocarbon being the best solvent. The variation of χ with composition and temperature is complex. Within the range of moderate polymer concentrations, the influences of composition decrease with increasing solvent quality. Additional effects become noticeable at the ends of the composition scale. The enthalpy parts (χ H ) and entropy parts (χ S ) of the Flory-Huggins interaction parameter, obtained from χ(T), vary considerably with composition and change their sign in some cases; these constituents of the Flory-Huggins interaction parameter do not permit a direct assessment of solvent quality. A clear-cut picture is, however, regained with a comparison of the interdependence of χ S and χ H . The elimination of explicit concentration influences re-establishes the order in the solvent quality setup via χ