Foamability of Ionic Micellar Solutions: Adsorption Kinetics and Supramolecular Surface Forces

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Aqueous micellar solutions of ionic surfactants play a significant role in diverse applications including biological membranes, fat-digestion, detergents, petrochemical processes, chemical catalysis, etc. Foams are ubiquitous as they exhibit a range of complex, unique and useful properties. The proposed research aims to develop the scientific and engineering foundations for understanding foam stability and formability of ionic micellar solutions. Obtaining comprehensive experimental data and developing methods for describing adsorption kinetics and supramolecular forces for ionic surfactants are primary motivations for this study. Another goal is to find quantifiable measures of heuristic criteria like foamability and foam stability and correlate them to physicochemical properties of surfactants to aid in the discovery of better surfactants, including biodegradable bio-surfactants.Foams contain a complex architecture of thin films and channels, and, at the molecular level, foam films are stabilized by surfactants. Layering of micelles in foam films results in stratification, manifested as stepwise thinning and coexistence of regions with different thicknesses. The layering contributes supramolecular oscillatory surface forces to disjoining pressure, that influence the stability of foam films. The proposed experimental and theoretical research focuses on understanding the adsorption kinetics and foam film stability of ionic surfactants, to quantitatively analyze the influence of charge on dynamical and equilibrium measurement of surface tension and disjoining pressure dominated by supramolecular structural forces. The PI proposes to correlate foamability to adsorption kinetics characterized by using maximum bubble pressure apparatus built by the PI's group and foam stability to supramolecular structural forces using a modified thin film balance apparatus. The theoretical effort will focus on developing a robust free-energy based framework for quantifying the influence of charge on both adsorption kinetics and supramolecular structural forces. A focused summer experimental research initiative is proposed to bring together a team of undergraduate students at UIC to conduct experiments in the realm of soft matter at interfaces. A course titled 'Fizzics and Interfacial Phenomena', developed by the PI, will be offered as an interdisciplinary elective to graduate and undergraduate students. Fizzics (or the science of drops, bubbles, emulsions and foams), optics, rheology and mechanics of complex fluids will form the basis for outreach activities. The participating students will develop several low-cost, robust instruments for studying interfacial phenomena and will make the instruments available to K-12 teachers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.