The poly(vinyl alcohol)-borate system: influence of polyelectrolyte effects on phase diagrams

The formation of a reversible gel by complexation of borate ions with poly(vinyl alcohol) is described. The complexation induces electrostatic charges on the polymeric chains. We focus on the behaviour of the system when the charges are partially screened by a passive salt. In such a case, 're-entrant phases' can be observed; they result from a delicate balance between the electrostatic repulsions among charged complexes formed on the polymeric chain and the crosslinking induced by borate ions. We present here an interpretation of the phase transitions based on a thermodynamic approach.