Adsorption of Surfactant Mixtures at Solid-Liquid Interfaces: A Study of Interactions and Dynamics Using Spectroscopic, Electrokinetic, and Calorimetric Techniques

9622781 Somasundaran Surfactants find use in several commercial processes but the inherent difficulty and excessive costs involved in preparing isomerically pure surfactants has necessitated the utilization of surfactant mixtures. Moreover, the performance of mixtures of surfactants is far superior to that of the individual components which has resulted in the deliberate addition of surfactant mixtures in many products such as detergents and cosmetics. The effectiveness of the surfactant in a majority of the application s depends upon the adsorption (or lack of it) as well as the microstructure of the adsorbed layers. Much work has been done to understand the mechanisms involved in determining adsorption of surfactants but very little of it has been with mixtures of surfactants. The key to the successful design of reagent combinations depends upon the understanding of the micro and nanostructural features of surfactant structures formed in solution and at solid-liquid interfaces coupled with the development of predictive models based upon the properties of individual components. It is the goal of the proposed research to investigate the interactions between surfactants of different characteristics and the micro and nanostructures of the mixed adsorbed layers using a multi-pronged approach combining classical tools of adsorption, electrokinetics, wettability and microcalorimetry with modern spectroscopic techniques such fluorescence, electron spin resonance (ESR), fluorescence recovery after photobleaching (FRAP), and second harmonic generation (SHG). Fluorescence and ESR spectroscopy will be used to determine the micropolarity, the microviscosity and aggregation numbers of the adsorbed layers; FRAP to probe the dynamics involved; SHG to probe the relative and absolute orientation of the molecules at the interface. Effects of pH, surfactant structure, salinity, temperature and perturbations in these parameters will be determined to assist in elucidating the adsorption mechanisms and associated dynamics. In addition to the surfactants such as linear alkyl aryl and xylene sulfonates, novel sugar based environmentally friendly surfactants will be a focus of the study. It is expected that the multi-pronged experimental and theoretical approach that has been successfully used for single surfactants will help in developing predictive useful models for adsorption of surfactant mixtures on solids. ***