Salt Effect on Swelling of Polyelectrolyte Networks with Brush-like Strands*

We study effect of added salt, density of ionized groups and molecular
architecture of the network strand on the swelling ability of networks with charged brush-like
strands using a combination of the analytical calculations and coarse-grained molecular
dynamics simulations. Analysis of the simulation results shows that in the salt-free case, when
swelling of polyelectrolyte networks is controlled by a fine interplay between the osmotic
pressure of counterions and nonlinear elasticity of the network strands, one can achieve a
significant increase in the network swelling ratio by increasing the grafting density and degree of
polymerization of the side chains. Addition of salt is manifested in the monotonic decrease of the
network swelling ratio with increasing the salt concentration. At high salt concentrations, the
electrostatic interactions between ionized groups are screened and swelling of the polyelectrolyte
networks is similar to that of networks with neutral brush-like strands immersed in a good
solvent. The computer simulation results are in a very good qualitative agreement with the
developed theoretical model accounting for nonlinear elasticity of the network strands.