Swelling and Deswelling

Polymer gels contain a large number of solvent molecules and can absorb additional solvent or lose solvent from the as-prepared state. These processes are of course accompanied by volume changes in the polymer gel, i.e., swelling and deswelling. This chapter discusses the swelling of polymer gels, including changes in elastic modulus due to swelling, the conditions for equilibrium swelling including the volume phase transition of neutral gels, and the kinetics of swelling and shrinking. It explains the bulk degradation behaviors of polymer gels. Generally, when a gel in its as-prepared state is immersed in a good solvent, the gel swells because the polymer constituting the gel is miscible in the solvent and osmotic pressure is generated. If no polymer exists in the solution outside the gel, osmotic pressure occurs due to the difference in the polymer concentrations inside and outside the gel.