Dynamical transition from diffusion to frustrated localization of polyelectrolyte in charged gels

Using Dynamic Light Scattering (DLS), we have investigated the dynamics of polyelectrolyte chains embedded in a polyelectrolyte gel matrix. The matrix is polyacrylamide-co-polyacrylate hydrogel with controllable crosslink density and charge density. The embedded polyelectrolyte is sodium polystyrene sulfonate (PSS) of molecular weight M and concentration C. For the gel alone, DLS exhibits essentially one diffusive mode representing the elasticity of the gel. When PSS is embedded inside the gel, DLS exhibits three modes at lower values of M and C: one gel mode, one PSS diffusive mode, and one PSS non-diffusive stretched exponential mode. At sufficiently higher values of C and M, there is only one PSS non-diffusive stretched exponential behavior, in addition to the elastic gel mode. Our results reveal a novel dynamical transition from chain diffusion to frustrated localization as the ratio of radius of gyration of PSS to the mesh size of the gel, as well as C, are increased.