Phase equilibria of hydrogel systems

Hydrogels are crosslinked polymers consisting of hydrophilic repeating units. Hydrogels are able to absorb/desorb large amounts of water and hydrophilic solutes, i.e. they swell/shrink in aqueous solutions. The volume change accompanied by that swelling can be continuous as well as discontinuous, i.e. phase transitions can be observed. This contribution aims to describe and discuss examples of the phase equilibrium behavior of hydrogel systems. Therefore, some typical examples of the swelling/shrinking of some simple synthetic hydrogels in water and in aqueous solutions are presented, the phase equilibrium conditions and a method for correlating/predicting such phase equilibria are discussed.