SWELLING AND COLLAPSE OF POLYMER GEL IN POLYMER-SOLUTIONS AND MELTS

Conformational changes in polymer networks swollen in solutions and melts of linear polymer chains are studied theoretically. The interaction of components is taken into account within the Flory-Huggins approximation, and the elastic free energy term is written in the Flory form. For the case of poly-electrolytic networks, the contribution of translation entropy of counterions is accounted for as well. It is shown that the variety of possible effects is not reduced to the contraction of the polymer network with the increase of concentration of linear chains. If the low molecular weight solvent is poor for the network chains, a jumpwise decollapse transition at high linear chain concentrations is possible. Discontinuous transitions can be realized even for networks composed of flexible and noncharged network chains if the length of linear polymer exceeds a certain critical value. For polyelectrolyte networks, conformational changes are mainly realized as discontinuous phase transitions; the amplitude of the jumps increases with the increase of the number of charges in network chains.