Discontinuous volume transitions in cross-linked polyelectrolyte gels induced by short-range attractions and strong electrostatic coupling

The swelling behavior of polyelectrolyte gels with and without short-range attraction was studied at variable permittivities using Monte Carlo simulations. The primitive model, with explicit treatment of all charged species augmented with an attractive square-well potential between network particles, was used. Discontinuous volume transitions appeared at critical values of the depth of the square-well potential at fixed permittivity and at critical values of the permittivity at fixed short-range potential. In particular, we observed such a transition also without the short-range potential. The collapsed state was favored by the short-range attraction and/or at low permittivity. The volumes of the collapsed states were 1-2 orders of magnitude smaller than those of the swollen states.