Droplet swimming in a pipe*

Self-solubilising droplets spontaneously self-propel in surfactant-saturated solutions as a result of the non-linear transport of surfactant molecules and micelles by their interfacial flows. While much is now known on the onset of propulsion and subsequent nonlinear dynamics in bulk fluids, the effect of confining boundaries is in general overlooked despite their ubiquitous relevance for experiments.  Recent experiments have indeed demonstrated the droplets' ability to swim inside small capillaries despite the increased resistance of lubrication flows.

Using a combination of numerical simulations and asymptotic analysis, we will show how the confining geometry profoundly modifies chemical transport and may in fact promote rather than prevent the swimming motion of chemically-active droplets.