Time‐dependence of boundary tensions of solutions. II. Experimental determination of the kinetics and equilibrium of adsorption at liquid‐liquid interfaces

Abstract

Abstract Boundary tensions have been measured by the method of pendent drops for the interfaces between water and solutions of long‐chain fatty acids in hexane over a wide range of concentrations. At low concentrations the interfacial tensions were independent of the age of the surface. But above what appeared to be a critical concentration, characteristic of each fatty acid, the interfacial tensions decreased with time to final equilibrium values. For very low concentrations, below about 5 × 10 −5 molal, the interfacial tension decreased linearly with concentration, the slope of the curve being identical for all the acids investigated (lauric, palmitic and stearic). In the concentration range where a time‐effect was observed, the fall in interfacial tension, and the time interval during which the fall occurred, both increased with increasing concentration. Experiments were carried out on the effect of varying temperature on the time‐effect. It was also shown that time‐effect occurred with an ester (ethyl palmitate).