ELASTIC AND QUASI-ELASTIC LIGHT-SCATTERING FROM MIXTURES OF 3 POLYMERS AND A SOLVENT - THE EFFECTS OF POLYMETHYLMETHACRYLATE CONCENTRATION AND MOLECULAR-WEIGHT ON THE PROPERTIES OF POLYSTYRENE POLYDIMETHYLSILOXANE TOLUENE SOLUTIONS

Elastic and quasi-elastic light scattering data obtained from PS/PDMS/ PMMA/toluene mixtures are reported. Several systems characterized by d ifferent concentrations and different molecular weights of PMMA are co nsidered. For each of these systems, a systematic investigation is per formed as a function of the scattering angle and the concentration of the PS/PDMS mixture using both techniques. The PMMA does not contribut e directly to the scattered light since its increment of refractive in dex is zero. However the data show that its presence modifies substant ially the apparent interaction parameter of PS and PDMS and the single diffusion coefficient of these polymers in the solution. The variatio ns of these quantities with the concentration and molecular weight of PMMA are obtained. The data are analyzed within a simplified model com bining based on the random phase approximation and the Rouse dynamics for ternary polymer mixtures. (C) 1995 John Wiley and Sons, Inc.