Swelling and collapse of polymer networks in contact with polymer melts and solutions

Thermodynamics of swelling of polymer networks in a solution or melt of another polymer has been analysed theoretically. The interaction between the components has been described in terms of the Flory-Huggins theory. With increasing incompatibility of the polymeric components, networks prepared in the presence of a large amount of solvent when in contact with an athermal melt of sufficiently long polymer chains, undergo a transition from swelling to segregation of the polymer components. A swelling regime is possible for networks in contact with a polymer solution such that the dimensions of the gel at first diminish with increasing concentration of the polymer in the external solution owing to a transition of the chains to a globular state; during the subsequent network expansion and the concentration of the linear polymer inside the gel increases in a stepwise manner.