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 mode l avoids the two process approach of Li and Tanaka, in which the solve nt motion is indirectly considered. Analytical solutions of solvent an d network movement are found from the collective diffusion equations f or 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 d irection and zia along the axial direction, respectively. Here r and z represent radial and axial coordinates, respectively, and a is the ra dius of the cylinder. The flow diagram of the solvent is obtained. It is also found that the solvent motion can be independently derived fro m Li-Tanaka's isotropy and continuity conditions without solving the c ollective diffusion equations. The swelling behavior is obtained at th e gel boundary and also in the interior of the gel.