Diffusion constants in polyacrylamide gels

The stimulated spin-echo method with pulsed magnetic field gradients was used to study the self-diffusion process of the fluid in swollen and collapsing polyacrylamide gels. Restricted-diffusion effects are evidenced by the dependence on the time of diffusion {Δ} of the diffusion constant Df. The results are interpreted in terms of the diffusion process through permeable barriers. A changeover in the time behavior of Df for the gel around the critical point is pointed out. The pseudodiffusion of the chains is investigated separately. Within the time scale of the experiment ({≤}100 ms) the squared dependence on the magnetic field gradient of the echo amplitude allows the definition of a local diffusion constant Dch for the monomer units. Dch depends on the measuring time in the form expected when restoring forces are active.