Experimental Evidence of Pure Layering at the Solid/Liquid Binary Mixture Interface. Silica/Water−2,5-Dimethylpyridine System

Abstract

Experimental evidence is brought for layering transitions at solid (silica) surfaces in contact with liquid mixtures, i.e., first-order transitions whereby the coverage of the surface jumps by an amount equivalent to one extra monolayer of 2,5-dimethylpyridine (2,5-DMP) adsorbed from a liquid mixture with water. These jumps are similar to surface phase changes whose aspects are all shown on the adsorption isotherms: coexistence of two values of adsorption for the same bulk equilibrium composition, adsorption plateaus, persistent metastability lines, characteristic evolution of the plateau's length with temperature, and the proximity of bulk demixing. Known for gas adsorption on a solid both experimentally and theoretically, this behavior is seen for the first time at a solid−liquid interface.