STUDY OF A FLUID-SOLID INTERFACE OVER A WIDE DENSITY RANGE INCLUDING THE CRITICAL REGION .1. SURFACE EXCESS OF ETHYLENE-GRAPHITE

The surface excess amount of ethylene adsorbed on graphitized carbon black has been measured over a pressure range from 1 to 120 bar using a high pressure microbalance technique. The data span a range of temperatures from 263 to 323 K (0. 93 less than equivalent to T/T//c less than equivalent to 1. 14) and a range of bulk densities up to rho / rho //c equals 1. 7. The results show the transition from the low-temperatures behavior (T less than T//c) with multilayer adsorption on approaching the saturation pressure, to the situation above the critical temperature T//c when the surface excess isotherms GAMMA sigma (P) exhibit a pronounced maximum at a pressure P//m//a//x greater than P//c. The dependence of P//m//a//x on temperature, and the variation of GAMMA sigma with temperature along the critical isochore, is determined quantitatively.