Thermodynamic treatment of some factors affecting the interaction between colloidal particles

Abstract

Classical thermodynamic methods are applied to a system of two spherical particles suspended in a medium in equilibrium in all respects other than interparticle separation. An expression similar to the Gibbs adsorption equation is derived which relates quantitatively changes in the free energy of interaction (ΔG) arising from changes in the medium composition to the differences in adsorption at the given separation and at infinite separation. This expression is generalised to any number of deformable particles of arbitrary shape. For a dilute two component solution, ΔG decreases on addition of solute if the amount adsorbed is greater in the given configuration than at infinite separation and vice versa. A similar expression also holds for the free energy of deformation of a single non-homogeneous body. The discussion is extended to include systems in partial equilibrium with respect to adsorption, and expressions are derived which relate the equilibrium and partial equilibrium forces and free energies of interaction of two particles. The application of the theory to particles with dissociable groups is outlined and it is shown how it can be used to discuss sol stability.