IMPACT OF BULK PHASE-TRANSITIONS AND WETTING TRANSITIONS ON ADSORPTION-ISOTHERMS IN BINARY-SYSTEMS IN CONTACT WITH SOLID

This paper presents several studies essentially on the solid/liquid in terface. The studied system is the liquid binary mixture water-2,5dime thylpyridine (2,5DMP) in contact with an amorphous silica (Aerosil typ e). The study of wetting along the two-liquid bulk phases coexistence in contact with silica allows the determination of a wetting transitio n temperature, which is an important parameter for the adsorption beha vior at coexistence. The adsorption isotherms in a diluted phase and i n a concentrated phase present some very significant features. In dilu ted solutions the isotherms show a succession of plateaus; these trans itions of layers persist in concentrated phases presenting a sequence of maxima and minima of relative adsorption (Gibbs adsorption) of 2,5D MP with respect to water. In concentrated solutions, they interfere wi th the prewetting that gives an original shape to the isotherms in con centrated solutions. These adsorption measurements were completed by a ctivity measurements which allow one to obtain the chemical potential of mixtures and linked information. The whole study shows the behavior of colloidal suspensions close to bulk phase changes. (C) 1998 Academ ic Press.