Diffusion of Polyelectrolytes in Polyelectrolyte Gels

We have studied diffusion of polyelectrolyte probe molecules in a similarly charged gel matrix. A variety of factors that affect the polymer diffusion inside the gel were explored such as the charge density and the cross-link density of the gel as well as the solvent quality and the salt concentration of the medium. In our study, the probe is sodium polystyrenesulfonate and the gel matrix is poly(acrylamide-co-sodium acrylate) gel. Using swelling studies and rheology, we characterize these synthesized gels under various salt concentrations. The diffusion of the probe was deduced based on dynamic light scattering studies of the polymer alone and the gel alone and then on the polymer diffusing inside the gel matrix. We show that in our system the reduced diffusion coefficient for the polymer inside the gel D similar to exp(-phi), where phi is the volume fraction of the equilibrated gel. Effects of the charge density and the cross-link density of the gel and the salt concentration and the quality of the solvent on the probe diffusion appear only through phi.