ADSORPTION-KINETICS OF ALKYLPHOSPHINE OXIDES AT WATER HEXANE INTERFACE .2. THEORY OF THE ADSORPTION WITH TRANSPORT ACROSS THE INTERFACE IN FINITE SYSTEMS/

A theoretical model is presented to describe the adsorption of surfact ant molecules at the water/oil interface for the case when transport a cross the interface must be considered due to the solubility of the su rfactant in both liquid phases (aqueous solution drop in an oil phase) . The theory is based on a diffusion-controlled adsorption model and a numerical difference scheme is used to solve the problem for closed f inite systems. By simulating adsorption-desorption processes, the infl uence of the geometrical and thermodynamic parameters on the dynamic a dsorption behavior is studied. In particular, the effects of the volum e ratio, surfactant concentration, diffusion coefficients, and distrib ution coefficient on the process are analyzed, The model allows quanti tative interpretation of the experimental data obtained for an alkyldi methylphosphine oxide at the water/hexane interface. The interfacial t ension signals, presenting a minimum under some conditions, are fitted by the theoretical curves. (C) 1997 Academic Press