Swelling and Deformation of Polyelectrolyte Gels in Salt Solutions

Polyelectrolyte (PE) gels consist of crosslinked polyelectrolyte chains and are featured by their incredible capability of water absorption which is found can be greatly affected by the salt content in the solution environment. In order to quantify this effect, we performed coarse-grained molecular dynamics simulations of swelling and deformation of the thick film-like polyelectrolyte networks immersed in a salt solution.  We study the swelling ability and shear modulus of PE gels made of linear chain and brush-like network strands and compare their behavior at different salt concentrations, fraction of the charged monomers per network strand, degree of polymerization between crosslinks and network preparation conditions. As expected, the gel swelling decreases with increasing salt concentration and decreasing the fraction of ionized groups per network strand while it increases with increasing the degree of polymerization between crosslinks. The gel mechanical properties in linear and nonlinear deformation regimes were obtained from simulations of the uniaxial deformation of the gels. These simulations have shown that there is a salt redistribution upon gel deformation with salt partition coefficient α= C_salt,gel/ C_salt increasing as gel deformation increases.