Oral: Adsorption Kinetics of Mixed Surfactant Systems at Air-Water Interface

The adsorption of mixed surfactants at the air-water interface is crucial for various applications, including cosmetics, food products, and lung therapeutics. While the equilibrium behavior of mixed surfactant systems is relatively well-explored, their kinetics remain poorly understood. In case of mixed systems, competitive and cooperative interactions lead to intriguing kinetic behaviors. To investigate this rich complexity, we employ both experimental approaches and theoretical modeling to quantitatively explain the kinetics of adsorption. Our custom-built capillary pressure tensiometer allows us to perform dynamic surface tension and dilatational rheology measurements. Using this we demonstrate experimentally, that a synergistic mixed micellar system exhibits a multi-step adsorption evolving over hours, deviating from the observations for single surfactants. A theoretical framework for the adsorption is modeled in terms of the underlying coupled kinetic adsorption-desorption at the interface and diffusion from the bulk. Our findings will contribute to identifying the rate-controlling mechanisms, and relevant timescales, important for controlling physical properties of mixed surfactant systems.