Adsorption Kinetics of Multicomponent Systems Comprising Ethoxylate Surfactants and Anionic Di-Rhamnolipid by Dynamic Interfacial Tension Measurement.

Abstract

Surfactants adsorb at interfaces and reduce the interfacial tension. In technical applications, they are typically used as complex mixtures rather than monodisperse systems. These mixtures often include ionic and non-ionic surfactants, with the non-ionic components comprising various monodisperse species. Such complexity influences adsorption behavior significantly. In this study, we therefore investigated how different monodisperse components within a technical surfactant system affect adsorption kinetics, characterized through dynamic interfacial tension measurements. We focused on blends of the anionic biosurfactant di-rhamnolipid and technical alkyl ethoxylates. Our results show that increasing the di-rhamnolipid ratio enhances the adsorption rate at interfaces logarithmically compared to ethoxylates, which is especially relevant for applications requiring rapid adsorption. Moreover, we observed partitioning effects of the ethoxylates' hydrophobic moieties when comparing adsorption at the oil/water and air/water interfaces. These differences explain why more hydrophilic ethoxylates are often preferred in practice. Overall, our findings deepen the understanding of adsorption behavior in mixed surfactant systems and provide a basis for tailoring formulations by adjusting the component ratio for specific application needs.