Dynamic Manipulation of Multiphase Fluids using Photo-Responsive Surfactants

Abstract:

The ability to control bubble and droplet motions is critical for enhancing efficiency and enabling new functionalities in applications such as electrochemistry, heat transfer, and biomedical systems. Photoresponsive surfactants provide a unique approach to dynamically manipulate these motions by generating surface tension gradients and inducing “photo-Marangoni” flows under light stimulation—without requiring engineered substrates. While prior studies have demonstrated effective manipulation using these surfactants, a fundamental understanding of how fluid behavior is governed by key parameters, including bubble and droplet size, surfactant photoswitching kinetics, concentration, and adsorption/desorption processes, remains incomplete due to the complex multiphysics interactions involved.



In this talk, I will present an integrated experimental and simulation-based approach to elucidate the governing mechanisms of light-driven fluid manipulation. Using a microgravity experiment, we isolate the photo-Marangoni force from competing effects such as buoyancy and natural convection to study bubble migration dynamics in a multiphase system. We investigate a custom-engineered photoresponsive surfactant, MCH-para, and analyze bubble migration velocity and acceleration across varying bubble sizes and illumination conditions. Additionally, I will introduce a numerical modeling framework that identifies optimal bubble size, photoisomerization kinetics, and adsorption/desorption parameters for maximizing migration velocity. This study provides important design guidelines for engineering next-generation photoresponsive surfactants to expand manipulation capabilities in multiphase fluid systems.