The Thermodynamics of Swelling

Abstract

An attempt has been made to bring together from the literature the important results of studies on swelling processes which have been made from the thermodynamic point of view. The quantities involved are swelling pressure, free energy, heat of swelling entropy and vollume contraction. Each is related either to the vapor pressure of the gel by equations derived by simple thermodynamic, methods, or is related to the water concentration of the gel by empirical formulas. A comparison of swelling pressure with osmotic pressure is made and it is demonstrated that both arise in the same fundamental process. Entropy changes with swelling are related to the distribution of the water molecules within the gel. Volume contraction is ascribed to the dissociation of ordinary water, which has a complex molecule, to the simple monomolecular form in the gel. Since swelling and capillarity are intimately related phenomena the important points of contact of the two are discussed.