The Gibbs Adsorption Equation and the Concept of the Gibbs Surface Excess

Department of Food Technology & Biochemical Engineering, Jadavpur University, Calcutta-700 032

A  critical . review of the Gibbs adsorption equation and the concept of the Gibbs surface excess have been presented. Relations between the surface excesses with the absolute composition of the interfacial phase of a binary solution has been discussed for water-organic liquid mixture and water-inorganic salt mixture. The interfacial phase for the water-organic solute mixture is a monolayer whereas that for the water-electrolyte mixture is multilayer in nature, The pressure area carves for charged and uncharged organic monobasic and dibasic acid monolayers at the oil-water and air-water interfaces have been examined in terms of limiting co-area, cohesional pressure, electrical free energy changes, counter-ion binding etc. The forms of the Gibbs adsorption equations for the multicomponent electrolyte solutions in terms of the kT -coeflicient have been discussed and its fields of applicability have been pointed out.