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 (3') to promote spontaneous dispersion is stressed. In this respect the importance of the point-of-zerocharge (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 3" 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 3" 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.

Size Tailoring of Magnetite Particles Formed by Aqueous Precipitation: An Example of Thermodynamic Stability of Nanometric Oxide Particles

“…Such an idea has already been proposed (23,24). To our knowledge, this work is the first experimental proof of such dispersions.…”

“…Adsorption of chemical species (HO Ϫ , cations of the electrolyte) and settling of the surface electrical charge must therefore induce a decrease in the interfacial tension with respect to its value at the point of zero charge (PZC), where the net surface charge is zero and the ionic strength no longer acts. Such an influence of the surface electrical charge on the oxide-solution interfacial tension has already been considered (22,23).…”

High Ionic Strength Promotes the Formation of Spherical Copolymer Particles

“…Such investigations should also consider the properties of AlCl 3 in water regarding coordination of water molecules but also hydrolysis and formation of polysalts. [35][36][37][38] Second, the peculiar role of phosphate coions is probably related to the variation in the pH value of the reaction mixture in dependence on the sodium phosphate concentration. Over the entire concentration range the pH, measured at room temperature after the polymerization, changes from 12-13 to 8-9 at the highest and lowest sodium phosphate concentration, respectively.…”

Pseudo‐polymorphic Behavior of Precipitated Calcium Oxalate

“…From this Stol and de Bruyn [16] derived an equation which splits the change in interfacial tension into a chemical and an electrostatic contribution:…”