Adhesion between silica particle and mica surfaces in water and electrolyte solutions

An atomic force microscope (AFM) is used to study the adhesion between a silica sphere and a mica plate in pure water and solutions of monovalent cations (LiCl, NaCl, KCl, and CsCl). It is found that the adhesive force depends not only on the electrolyte concentration but also on the hydration enthalpy of cations and the contact time of the particle on the surface. Possible mechanisms by which the observed phenomena can be explained consistently are discussed extensively. It is suggested that the adhesive force is closely related to the structure of the layer of cations and water molecules adsorbed on the surfaces: the strong adhesive force is obtained when highly hydrated cations (Li⁺, Na⁺) are adsorbed to form a thick but weakly adsorbed layer, while the weak adhesive force is observed when poorly hydrated cations (Cs⁺, K⁺) are adsorbed to form a thin but strongly adsorbed layer. (C) 2000 Academic Press.