PROBE DIFFUSION IN POLYMER-SOLUTIONS IN THE DILUTE SEMIDILUTE CROSSOVER REGIME .2. POLYELECTROLYTES

The Stokes-Einstein relationship has been tested for the motion of polystyrene latex particles moving through two different polyelectrolytes, sodium poly(styrene sulfonate) and poly(L-lysine) (PLL). The motion of the particles, which are negatively charged, through sodium poly(styrene sulfonate) solutions shows deviations corresponding to a greater slowing down of the particles than expected from measurements of the macroscopic viscosity. This behavior is similar to that seen for a neutral polymer and is thought to be due to the effect of tails in the adsorbed layer. In contrast, PLL initially showed an apparent speeding up of the particles. However, as the concentration of PLL was raised, a steep increase in the ratio of the viscosity calculated from sedimentation to that directly measured was found. This behavior is attributed to a change in the conformation of the adsorbed layer from a rather flat configuration at low concentrations to a much more extended one at high concentrations, when interchain screening of charges allows the molecule to become more flexible.