Viscosity of polymer/solvent systems: Quantitative description on the basis of molecular surfaces

A model for the description of the viscosity of polymer/solvent systems mad e up of homologues, developed earlier, is generalized to normal polymer sol vent mixtures. It is based on three premises: (i) the dissipation of energy takes place at the molecular interfaces; (ii) the friction between solvent and solute varies with composition due to a change in the flow mechanism ( drainage of coils); and (iii) the specific coil volume generally also depen ds on polymer concentration. The resulting simple expression contains four system-specific parameters: a geometric factor gamma, which accounts for th e differences of the surface to volume ratios of the components; a viscomet ric interaction parameter a, which measures the friction between solute and solvent in the case of fully draining polymer coils; [eta], the specific h ydrodynamic volume of the polymer at infinite dilution (intrinsic viscosity ), and [eta](Theta) the specific hydrodynamic volume under Theta conditions . The suitability of this model is demonstrated by means of extensive exper imental data reported in the literature for the systems diethyl phthalate/p oly(vinyl acetate) and diethyl phthalate/poly(methyl acrylate). It appears worthwhile to mention that the evaluation yields [eta] and [eta](Theta), ev en in the absence of information within the relevant composition range, and that there exists a linear correlation between gamma and alpha. (C) 2000 T he Society of Rheology. [S0148-6055(00)00503-9].