Time‐dependence of boundary tensions of solutions: IV. Kinetics of adsorption at liquid‐liquid interfaces

Abstract

Abstract Various mechanisms are considered which might explain the variation of interfacial tensions with time, when fatty acids are adsorbed from hexane on to a hexane water interface. In these solutions there are both single and associated molecules of the fatty acids. Although the single molecules are the adsorbable species, it is shown that the slow adsorption cannot be attributed to their relative scarcity. The Langmuir adsorption isotherm is found not to apply accurately at equilibrium, and a new isotherm is proposed. A mechanism is suggested to explain the kinetics of adsorption and desorption and is found to be in accordance with the experimental variation of interfacial tension with time. Velocity constants for adsorption (k t ) and desorption (k 2 ) are evaluated. The resulting equilibrium constants (k 1 /k 2 ) are found to agree well with equilibrium constants deduced thermodynamically by an entirely independent process. The effect of temperature on the processes of adsorption and desorption is also discussed.