Fractional coefficient of macromolecules in concentrated solution and in the vicinity of the critical solution temperature. Diffusion and sedimentation studies of polystyrene in toluene and trans-decalin

Abstract

The concentration dependence of the frictional coefficient ( f) in concentrated solutions of well-defined polystyrene fractions has been studied both in a good solvent (toluene) and in a solvent where θ conditions and condition in the vicinity of phase separation can be realized ( trans-decalin). f and the self-diffusion coefficient ( D +) have been calculated from a combination of measured translational diffusion coefficients ( D) and osmotic pressure data for the systems; polystyrene (M = 390 000) trans- decalin up to 90 kg/m 3 at 20° (θ-conditions), 30° and 40°C; polystyrene (M = 110 000) toluene up to 120 kg/m 3 at 25°C. Sedimentation measurements are also reported. The main results are: (a) over a concentration interval 0–100 kg/m 3, f shows more than a ten-fold and almost linear increase; (b) in trans-decalin when the temperature is raised from 20° (θ-conditions) to 40°C (good solvent conditions), keeping the concentration constant, f increases only slightly, the increase being somewhat more pronounced at higher concentrations; (c) the concentration dependence of the ratio D D + is considerable under good solvent conditions but becomes gradually less pronounced when θ-conditions are approached; (d) diffusion/osmosis and velocity sedimentation give identical values of f over the entire concentration interval.