  The swelling kinetics of charged polymer gels reflect the complex competition
among elastic, mixing, and ionic contributions. Here, we used dynamic light
scattering to investigate the collective diffusion coefficient of model gels,
whose polymer network structure was controlled so that the three contributions
were comparable. We demonstrate that the collective diffusion coefficient stems
from the sum of elastic, mixing, and ionic contributions, without evident
cross-correlations. The significant ionic contribution conforms to the Donnan
equilibrium, which explains equilibrium electrical potential gradients in
biological systems.
