TEMPERATURE-DEPENDENCE OF PROBE DIFFUSION IN SOLUTIONS OF LOW-MOLECULAR-WEIGHT POLYELECTROLYTES

Optical probe diffusion measurements were made on aqueous solutions of 2/3-neutralized poly(acrylic acid), molecular weights 5 and 150 kDa, both in salt-free systems and in systems containing 0.1 M NaCl. The probe particles were 204-angstrom-radius carboxylate-modified polystyrene latex spheres. The temperature dependence of the probe diffusion coefficient D(p) is entirely explained by the temperature dependence of the solvent viscosity, no correction for a distance from a hypothesized glass temperature T(g) of the solution being needed. For these systems, the hypothesis that the concentration dependence of D(p) (as described by the universal scaling law D(p) = D(p0) exp(-alpha-c-nu)) is due to the concentration dependence of T(g), rather than being due to hydrodynamic interactions between polymer chains, is clearly rejected by our measurements.