Binding of Solute and Solvent at the Interface and the Gibbs Surface Excess

Introduction With the help of an imaginary mathematical plane placed at the interfacial region, a liquid-gas system, according to the Gibbs concept, may be divided into two phases. From the thermodynamic analysis of such a system, Gibbs also derived his well-known equation relating the surface excess of solute with the surface tension and bulk activity of the solute in solution. The physical concepts associated with the Gibbs surface excess have been examined more critically by Guggenheim and Adam ( 1 ) and also by Defay and Prigogine ( 2 ). Guggenheim ( 3 ) has also given an alternative derivation of the Gibbs adsorption equation assuming certain arbitrary but finite values for the physical thickness of the interfacial phase. In some cases, the interfacial thickness may be estimated from the experimental data ( 4 ). Goodrich ( 5 ) has recently analyzed the Gibbs adsorption equation with the help of an algebric method in which no mention is made of