ABSTRACT
Electrostatic effects are among the main factors which determine the state of ioncontaining gels. These effects can favor either the gel swelling or the gel collapse [1, 2].
Let us consider a gel with a small fraction of ionizable monomer units. Pronounced gel swelling is usually observed in polyelectrolyte regime; that is, in the case when ioncontaining groups are fully dissociated with the formation of charged monomer units and free small counterions, neutralizing the network charges (Fig. 1). Free counterions try to occupy as much volume as possible in order to gain in the translational entropy, but they cannot escape outside the gel because of the condition of macroscopic electroneutrality. As a result they create an exerting osmotic pressure leading to gel swelling. In the polyelectrolyte regimen, the presence of only 5 mol% of charged repeat units in polymer gel chains can induce gel swelling by two orders of magnitude (in comparison with its uncharged state) [3].
