Surfactant transfer across a water/oil interface: A diffusion/kinetics model for the interfacial tension evolution

The transfer of amphiphilic solutes through an interface between water and an organic solvent has been studied numerically by simulations based on a general diffusion/reaction model. This description predicts the evolution of the solute concentrations and the transfer across the liquid/liquid interface. It especially focuses on the dynamic interfacial tension evolution that can be measured by a pendant drop tensiometer. Both the bulk diffusion and the adsorption/desorption rate on both sides of the liquid interface are assumed to contribute to the global transfer kinetic. The calculations provide an understanding on how kinetic exchange at the interface and diffusion transport through the bulk determine the dynamic interfacial tension evolution. In particular, complex interfacial tension evolutions with a non-trivial behavior are predicted in some special cases when diffusion and kinetic exchange are of the same order of magnitude. Finally, this model is used to re-interpret experimental data about Triton X-100 transfer at a water–oil interface.