An Analytical Model for Estimation of the Self-Diffusion Coefficient and Adsorption Kinetics of Surfactants Using Dynamic Interfacial Tension Measurements.

We report a new analytical approach to model the transient diffusion and adsorption kinetics of a surfactant at a liquid/liquid interface using dynamic interfacial tension data. The developed model combined with the Frumkin/Langmuir isotherm is used to reproduce the experimental data of dynamic interfacial tension and predict the surfactant diffusion coefficient from a bulk solution to an interface and its adsorption kinetics. Experimental data of the dynamic interfacial tension of toluene and heptol solutions at various concentrations of asphaltenes (a natural surfactant) were employed to examine the ability of the developed model to regenerate the dynamic interfacial tension data. The model enabled us to estimate the apparent diffusion coefficient and adsorption kinetics of asphaltenes at different concentrations. The results showed that the diffusive migration of asphaltene toward an oil/water interface decreases at its higher concentrations and increases at higher concentrations of an aliphatic solvent such as -heptane. Furthermore, the results reveal that the adsorption rate of asphaltenes at the interface increases at higher concentrations of surfactants and the aliphatic solvent. The developed analytical model finds applications in the prediction of the diffusion and adsorption kinetics of surfactants using dynamic interfacial tension data.