Surfactant-induced dissipation in sheared foams: Mechanics and thermodynamics

Though the influence of surfactant type on foam rheological properties is well established experimentally, the underlying physical mechanisms are far from understood. Here, using fully resolved numerical simulation of an elementary T1 event taking into account both flow and surfactant dynamics, we unveil the origin of surfactant-induced dissipation in sheared foams. To model the diffusive and exchange contributions, we revisit the classical Lucassen model by switching from a mechanical to a thermodynamic perspective, and we find that in spite of its extreme simplicity, it captures well some behaviors of our numerical foam. Our approach should be useful in the class of surfactant-controlled systems, from soap films and emulsions to coating films and spreading droplets.