Hydrodynamic response of a surfactant-laden interface to a radial flow

TL;DR

This paper investigates how surfactants at a liquid-air interface significantly alter the flow dynamics caused by a submerged jet, changing boundary conditions and offering a method to detect impurities.

Contribution

It provides analytical and numerical insights into the impact of surfactants on radial flow and interface elasticity, highlighting a new approach to quantify impurities.

Findings

Surfactants induce in-plane elasticity that modifies flow morphology.

Flow boundary conditions shift from slip to no-slip with decreasing surface compressibility.

Small amounts of surfactants can be detected by analyzing flow response.

Abstract

We study the features of a radial Stokes flow due to a submerged jet directed toward a liquid-air interface. The presence of surface-active impurities confers to the interface an in-plane elasticity that resists the incident flow. Both analytical and numerical calculations show that a minute amount of surfactants is enough to profoundly alter the morphology of the flow. The hydrodynamic response of the interface is affected as well, shifting from slip to no-slip boundary condition as the surface compressibility decreases. We argue that the competition between the divergent outward flow and the elastic response of the interface may actually be used as a practical way to detect and quantify a small amount of impurities.