Abstract
Understanding how microscopic interfacial mechanics govern macroscopic stability is central to systems as diverse as foams, emulsions, wetting/dewetting, microfluidics, and pulmonary function. Using a dynamic thin-film balance, we investigate surfactant-stabilized air/liquid films and directly visualize asymmetric concentration fields and convective flows in charged and uncharged lipid systems. The results reveal an interplay between Marangoni stresses and disjoining pressure, where localized surfactant depletion both drives lateral stresses and weakens structural forces, redistributing stresses across the film and prolonging lifetimes. These mechanisms of stress balancing and redistribution at the microscale find a striking parallel in lung surfactant physiology. Pulmonary surfactant layers not only reduce surface tension but also undergo nonequilibrium structural rearrangements that are essential for sustaining compliance and preventing alveolar collapse. Interfacial rheometry, neutron reflectometry, and Raman analysis demonstrate how periodic sighs enrich the interface with saturated lipids, inducing compressional hardening and transforming the layer into a mechanically robust DPPC-rich film. These findings underscore the importance of compressive interfacial stresses, in addition to surface tension reduction, for both thin-film stability and lung function. Taken together, they provide a unified mechanistic framework for interfacial stress regulation across applications, from the design of stable foams and emulsions to improved strategies for pulmonary therapies.
About the Speaker
Jan Vermant is a professor of Soft Materials at ETH Zurich in Switzerland. He received his chemical engineering degree and doctorate from KU Leuven in Belgium. The research of his group centers on the rheology-structure relations in bulk and at interfaces.
Hosts: Professor Randy Ewoldt (MechSE) and Professor Simon Rogers (ChBE)