Kinetics of Surfactant Adsorption at Fluid-Fluid Interfaces: Surfactant Mixtures

TL;DR

This paper presents a theoretical study of surfactant mixture adsorption kinetics at fluid-fluid interfaces, deriving equations, solving them analytically and numerically, and comparing results with experiments to understand the influence of mixture composition.

Contribution

It introduces a theoretical framework for surfactant mixture adsorption kinetics, including derivation of kinetic equations and analysis of coupled species effects.

Findings

Characteristic time scales of adsorption identified

Mixture kinetics differ significantly from single-surfactant solutions

Good agreement with experimental data observed

Abstract

The adsorption at the interface between an aqueous solution of several surface-active agents and another fluid (air or oil) phase is addressed theoretically. We derive the kinetic equations from a variation of the interfacial free energy, solve them numerically and provide an analytic solution for the simple case of a linear adsorption isotherm. Calculating asymptotic solutions analytically, we find the characteristic time scales of the adsorption process and observe the behavior of the system at various temporal stages. In particular, we relate the kinetic behavior of the mixture to the properties of its individual constituents and find good agreement with experiments. In the case of kinetically limited adsorption, the mixture kinetics is found to be considerably different from that of the single-surfactant solutions because of strong coupling between the species.