The emulsification of inorganic colloidal particles in an organic medium

Colloidal suspensions of inorganic particles in xylene could be prepared by means of reactions between two solid powders. In all cases, the reagents were transported to the reaction sites by means of a microemulsion of the reverse type containing a surfactant, water and tetrahydrofuran as a cosurfactant. This process, where colloidal particles are formed and emulsified from a chemical reaction site at the surface of a solid, is illustrated with examples of the synthesis of particles containing calcium thiophosphate, calcium hydroxide or sodium phosphate. The role of the cosurfactant was to speed up the transport rate of the reagents, allowing a high yield of colloidal particles and the control of side reactions in the case of calcium thiophosphate synthesis. The mechanism by which the inorganic particles were emulsified is still an open question and this is discussed. The particle sizes did not depend on the amount of surfactant as in the case of classical emulsions. The type of inorganic product formed inside the reverse micelles and the spontaneous curvature of the surfactant film appear as the most relevant parameters which control the particle size.