Thermodynamic stabilization of colloids

Abstract

An analysis is given of the conditions necessary for obtaining a thermodynamically stable dispersion (TSD) of solid particles in a continuous aqueous solution phase. The role of the adsorption of potential-determining ions at the planar interface in lowering the interfacial free energy (γ) to promote spontaneous dispersion is stressed. In this respect the importance of the point-of-zero-charge (PZC) and of the point-of-zero-surface tension (PZS) in the quantitative description of the dispersion process are discussed. It is reasoned that for simple inorganic solids a decrease in y by about 200 mN m−1 relative to its value at the PZC may be sufficient to yield a TSD. The equilibrium dispersion will be characterized by a very small but positive y and a near isodispersity. Suggestions are made for preparing by precipitation dispersions which may prove to be thermodynamically stable. The differences and similarities between these dispersions and the well-known kinetically stabilized sols of lyophobic colloids are briefly enumerated and discussed.