Intranetwork phase separation in polyelectrolyte gels

We have investigated the swelling behavior of polyelectrolyte gels in a low-molecular-weight solvent taking into account the possibility of intragel phase separation. We have shown that, as for the case of a neutral gel considered recently by Moerkerke et al., the coexistence of two phases differing by polymer concentration can also take place inside the polyelectrolyte gel if the amount of solvent is not enough to ensure its free swelling. The phase diagrams for polyelectrolyte gels with various degrees of ionization and with various degrees of stiffness of the gel subchains have been calculated. It has been shown that the region of stability of the two-phase gel increases significantly with increasing number of charges on the network chains and chain rigidity.