Diffusion of polymers through polyacrylamide gels

The diffusion of rhodamine dye and poly(acrylic acids) (M_W = 6000, 50 000 and 150 000) through polyacrylamide (PAM) gels has been studied. Diffusion coefficients were calculated by following the diffusion of the species out of PAM gel cylinders into the surrounding liquid. The effect of gel structure on diffusion was tested by making gels with varying monomer and crosslinker concentrations. The pore sizes in the gels were calculated from modulus measurements on the gels, and the effect of the ratio of diffusing species size to gel pore size was investigated. The diffusion coefficients decreased in a power-law fashion with increased molecular weight of the diffusing species, decreased with increased monomer concentration, and decreased with increased crosslinking. The partition coefficients of the species, as measured in the experiments, depend on competition between attractive hydrogen-bonding forces and repulsive entropic forces.