CHANGE OF MICROSCOPIC FRICTION IN CONCENTRATED POLYSTYRENE SOLUTIONS

Measurements of microscopic friction in two concentrated polystyrene solutions are reported over a broad temperature and concentration range as obtained from depolarized Rayleigh scattering and dielectric spectroscopy. The microscopic friction is extracted from the degree of alteration of the solvent reorientation by the presence of polymer chains. The dependence of the solvent microscopic friction on polymer concentration changes from an exponential law at high temperatures to a much stronger dependence at temperatures near the solvent glass transition, T-g. In addition, toluene molecules experience a greater friction than dioctylphthalate in the concentrated polystyrene solutions when compared at (low) temperatures equidistant from the solvent T-g. There is a reversal of the solvent microscopic friction in the two systems in going from high to low temperatures as a result of the greater difference between the two timescales for the more mobile solvent (toluene).