In general, wetting of pore surfaces may not be perfect, lated for different values of two parameters that characterize the and partial wetting may occur. In this case an adsorption range of action of surface forces and corresponding decay length.
isotherm G(p/p s ) must intersect the G-axis at some finite In the case of partial wetting of a solid surface, isotherms conadsorption value G 0 . Schematic representations of adsorption sisting of two exponential terms were used, as was proposed earlier by A. Adamson. Equilibrium contact angles that are formed with isotherms corresponding to the cases of complete and partial droplets of bulk liquid were calculated using the Frumkin-Derjawetting are shown in Fig. by curves 1 and 2, respectively. guin approach in dependence on the parameters of isotherms. Therefore, the amount of adsorbed vapor depends on wetting Calculations of contact angles that are formed between convex conditions. When wetting conditions degrade, the difference capillary menisci in thin pores, at relative vapor pressure lower between two these isotherms increases.
than 1, have shown that a transition from partial wetting of a lone
Correction for partial wetting is also of importance when solid surface (at p/p s Å 1) to complete wetting in thin pores (at capillary condensation is considered. Meniscus curvature in p/p s õ 1) may occur. Corresponding threshold values of relative thin pores depends on the equilibrium film thickness that vapor pressure and pore radii were calculated. In the case of comcover the pore surface. Besides, the contact angles depend plete wetting, corrections for capillary pressures that arise due to on the whole form of the isotherm, even in the region of formation of a transition zone between wetting films and curved super saturation (1). Correct calculation of capillary presmeniscus surfaces were estimated. The calculations are limited by the values of relative vapor pressure near saturation when thick sure in dependence of pore sizes demands supplementary enough wetting films are formed on pore surfaces. Due to the information both on adsorption film thickness and contact application of model isotherms with some adopted parameters, the angles. Even in the cases of complete wetting capillary presresults obtained are qualitative in nature. However, the methods of sures are higher than calculated, using the Kelvin equation, calculation developed for the excess free energy of solid surfaces due to the formation of a transition zone between films and covered with thin adsorption of thicker wetting films and of conmenisci (2). Therefore, the degree of hydrophilicity of pore tact angles outside and inside thin pores may be of general interest. surface influences not only the adsorption isotherm but also