Swelling kinetics of polymer gels

The kinetics of gel swelling is theoretically analyzed by considering coupled motions of both the solvent and the polymer network. This model avoids the two process approach of Li and Tanaka, in which the solvent motion is indirectly considered. Analytical solutions of solvent and network movement are found from the collective diffusion equations for a long cylindrical and a large disk gel. For a cylindrical gel, the speed of solvent motion is proportional to -r/(2a) along the radial direction and zia along the axial direction, respectively. Here r and z represent radial and axial coordinates, respectively, and a is the radius of the cylinder. The flow diagram of the solvent is obtained. It is also found that the solvent motion can be independently derived from Li-Tanaka's isotropy and continuity conditions without solving the collective diffusion equations. The swelling behavior is obtained at the gel boundary and also in the interior of the gel.