TOTAL SURFACE SEGREGATION - A FRESH LOOK AT THE GIBBS ADSORPTION-ISOTHERM FOR BINARY-LIQUID MIXTURES

A quantity termed the total surface segregation is discussed and evalu ated as a measure of relative adsorption at the gas-liquid interface o f binary liquid mixtures. Its calculation from the surface tension and nonideality of the liquid mixture is detailed, and results are presen ted for 17 systems covering the recognized classes of liquid mixtures. The results for argon + krypton, in particular, are compared with the oretical calculations based on the density functional treatment of Tel o da Gama and Evans which yields the local surface segregation whose i ntegral through the interface is a close approximation to the total su rface segregation. The absolute magnitude, composition dependence, rel ation to surface azeotropy (aneotropy) and bulk azeotropy, and proximi ty to a consolute point of the total surface segregation are explored. Useful relationships with the known underlying intermolecular forces are presented which confirm broadly the utility of the total surface s egregation for the purpose of representing adsorption at the gas-liqui d interface of mixtures.