Dynamic Surface Tensions of Aqueous Surfactant Mixtures:  Experimental Investigation

• Published in: Langmuir 2001-11, Vol.17 (24), p.7494-7500
• Main Authors: Mulqueen, Michael, Datwani, Sammy S, Stebe, Kathleen J, Blankschtein, Daniel
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la010782p

We present an experimental investigation of the interfacial behavior of aqueous solutions of two nonionic surfactants and their binary mixture. Specifically, we measure both the equilibrium surface tensions (using the Wilhelmy plate method) and the dynamic surface tensions (using the pendant bubble technique) of aqueous solutions of two nonionic alkyl ethoxylate surfactants, dodecyl penta(ethylene oxide) (C12E5) and decyl octa(ethylene oxide) (C10E8), as well as of their binary mixture. These measurements are then compared with the predictions made using recently developed molecular-thermodynamic theories of the equilibrium and the dynamic interfacial behaviors of nonionic surfactant mixtures and are found to be in good agreement. The main advantage of the equilibrium and the dynamic interfacial theories adopted here is that they are based on the molecular characteristics of the surfactants, and as such, the required number of experimentally determined parameters can be reduced significantly. Indeed, no experimental measurements, neither of the equilibrium nor of the dynamic type, need to be conducted on the mixed surfactant solutions. In addition to the complete prediction of the dynamic surface tensions and the dynamic surface concentrations, the theoretical framework also includes a simplified time scale analysis of the dynamic interfacial behavior that allows “quick” insight into the relationship between the molecular structure of a surfactant and its dynamic interfacial behavior. The experimental measurements also show that the simplified time scale analysis of the dynamic interfacial behavior provides an approximate, yet quantitatively accurate, description of the rate of adsorption, measured through the dynamic surface tension, of the single nonionic surfactants as well as of a surfactant component in the binary mixture of nonionic surfactants.