Hydrophobic and Electrostatic Interactions in Adsorption at Interfaces: · Relation to the Nature of Liquid Surfaces

Electrostatic .and .hydrophobic interactions of ions near interfaces are examined in relation to the nature and structure of surfaces of. liquids, esp~cia.lly that of water. The superficial excess entropy and energy of liquid surfaces is calculated from surface tension data, aind Stefan\u27s ratio is evaluated for several liquid interfaces. Stefan\u27s ratio is related to the ratio of co-ord~nation number of surface molecules to that for bulk molecules and leads to information on surface structure. Stefan\u27•s ratio is ca. 0.5 for non-polar liquids but is near 0.1 for H-\u27bonded liquids. The superficial excess entropy is related to the cohesive energy density and to co-ordination i,n the surface. Short-range ·effects in adsorption of ions at air/water interfaces are determined by the structure of the liquid surface and by electrostatic polarization energy near the interface. Based on the Born equation, relations are · deduced for ionic adsorption near liquid interfaces. By studying the adsorption of a series of propylamine perchloratesat the air/water interface and the correspond1ng surface potential changes, the relaEve . importance of hydrophobic and electrosrtatic ion-solvent interaction effects was investigated. Methods for investig~ting the entropy of water at charged interfaces are discussed and a theory of entropy of water· in the double-layer is reviewed