2023/12/22(Fri) 11:00 -12:00 一樓演講廳 1F, Auditorium
Title
Soap spreading on water - A superficial relationship
Speaker
Prof. Mahesh Bandi (Okinawa Institute of Science and Technology)Abstract
Surfactants such as soap when introduced at a liquid interface give rise to Marangoni stresses that drive a flow. This fundamental process of surfactant spreading, governed by its diffusion and transport via self-induced flow has many applications from materials chemistry to biomechanics. Most surfactants we use are soluble in the fluid and can be transported in a phase dissolved in the bulk or adsorbed at the interface. But a complete description of the resulting flow is hindered by the complexity of surfactant dynamics, which includes characterizing the equilibrium adsorption characteristics, the adsorption-desorption kinetics and transport by the flow. Whereas methods based on molecular or radiometric markers can measure surface excess during a flow, low surfactant diffusivity into bulk fluid renders bulk concentration measurements at the interface difficult during flow. Direct Marangoni stress measurements via in situ surface tension gradient measurements are equally challenging. Simultaneous access to bulk and surface concentrations, Marangoni stress, sorption kinetics, and their subsequent correlation with each other to deduce the surfactant dynamics present an experimentally formidable task. In this talk, I will detail a set of experiments in stationary Marangoni-driven surfactant transport to discriminate between two limiting scenarios: one where the surfactant remains adsorbed at the interface as it spreads and the other where it dissolves into bulk fluid during the spreading. I will show that it is possible to distinguish between these two limiting cases through purely hydrodynamic signatures, without using any knowledge of the surfactant physicochemical properties because either of these assumptions reduces the complexity of the problem by enabling semi-analytical steady solutions to the governing equations. The objective in this setting then becomes one of experimental validation of these assumptions using hydrodynamic measurements alone.
Language
演講語言 (Language): in English
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