Adsorption kinetics of alkyl phosphine oxides in water/alkane systems with transfer across the interface

The adsorption kinetics of alkyl phosphine oxides soluble both in water and in alkanes has been experimentally studied by measuring the dynamic interfacial tension. To this aim the pendant drop method was used with an automatic acquisition of the drop shape (ASTRA). The experimental results show that under particular geometrical and initial conditions, the dynamic interfacial tension exhibits a minimum. This nonmonotonic behaviour can be explained by considering the transfer of matter through the surface during the adsorption and the depletion of one phase necessary to establish the partition equilibrium. These data can be interpreted on the basis of a diffusion controlled adsorption model involving two finite phases. Moreover a particular experimental procedure for measuring the partition coefficient has been used based on the equilibrium surface tension measurements and on the evaluation of the adsorption isotherm.