ABSTRACT
This chapter demonstrates the use of a thermodynamic modeling approach in describing sorption and swelling equilibria as well as swelling kinetics of ion exchange resins. It derives a general condition for phase equilibrium in rubbery cross-linked polymers by using thermodynamics of polymer solutions and rubbery materials. The chapter presents a number of models commonly used for describing the elasticity of gels and calculating the swelling pressure in the gel phase. It also presents shear modulus data obtained from direct mechanical measurement of single particles and swelling pressure data obtained from vapor sorption isotherms. The chapter also demonstrates how the elastic properties of the resin can be taken into account in a relatively simple manner by including them in the chemical potential driving force for diffusion. For rubbery polymers, swelling and shrinking kinetics in solvent mixtures is controlled by diffusion of liquids inside the particle.
