Critical wetting, flocculation of silica particles in near-critical lutidine–water mixtures and related phenomena

Abstract

An interpretation of critical wetting and flocculation phenomena is given, referring mainly to silica dispersed in lutidine–water mixtures. The critical wetting behaviour of other systems, e.g. perfluoromethylcylohexane on alcohols, and the wetting of immersed solids, is made easier to understand. The silica flocculation is preceded by the formation of a thick adsorption layer on the silica, which then coalesces to the floc state. The wetting behaviour probably depends on the solid, giving a family of curves. Flocculation at the critical point is delayed until the coexistence curve is reached, because at the critical point the contact angle made by the interface formed between the conjugate phases and the solid would be 90°. The implications for related phenomena, and for applications such as the partitioning of particles between two-phase liquids are discussed.