Physical Adsorption of Fluids at High Temperatures and High Pressures

The asymptotic relation for the one‐particle distribution function of a fluid near a flat surface, obtained by Kuni and Rusanov, is used to calculate the adsorption at the fluid/solid interface. According to this theory the surface excess of the fluid as a function of pressure and temperature is approximately proportional to p2K, where p is the density and K the isothermal compressibility of the bulk fluid. The main features of published adsorption isotherms at high temperatures (T > 2 Tc) of the adsorptive, i.e., the initial increase of the surface excess and its decrease at higher pressures, as well as the temperature dependence of adsorption, are reproduced by this theory.