Contribution of structural forces to wetting of quartz surface by electrolyte solutions

Based on disjoining pressure isotherms of wetting films, contact angles on quartz are calculated for aqueous KCI solutions with concentrations varying from 10(-4) to 1 M and pH from 2 to 10. The Stern potentials of the quartz surface Psi(1) and potentials of the film-gas interface Psi(2) calculated by data on the bubble electrophoretic mobility are used in this case. In co ntrast to earlier calculations, we applied a more general solution of the t heory of electrostatic forces unbound by low electrolyte concentrations. We succeeded in obtaining an agreement between theoretical and experimental v alues of contact angles, with allowances made only for the parameters of st ructural forces K and lambda as adjustment parameters. These parameters are determined similarly as in colloid chemistry by the difference between the results of direct measurements of forces acting between model bodies in aq ueous solutions and those calculated by the DLVO theory including only mole cular and electrostatic forces. Dependences of the characteristics of struc tural forces on the solution concentration and pH were obtained and their r elation with the surface charge was demonstrated. The possibilities of cont rolling wetting by the variation of the contribution of various components of surface forces to free surface energy of a film are discussed.