Stop-and-go, swirling and self-throttling: Active droplets driven by chemohydrodynamic instabilities

Fluid-based active matter has gained lively interest in both experiment and numerics as a versatile system to study active processes from single agents to collective scales.

One hallmark of active or living matter lies in the conversion of microscopic free fuel energy to mesoscopic directed motion, generally in absence of external forces. This mesoscopic motion can be complex and sophisticted, involving rotational or helical states, switching run-and-tumble dynamics, or arrested feeding states. In nature, these states are usually driven by complex swimmer mechanics, geometry, or multi-step biochemical pathways.

However, similar periodic or chaotic states may also arise simply from the nonlinear dynamics of fuel conversion that set autophoretic droplet swimmers in motion, leading to a wealth of unexpected biomimetic phenomena. In this talk, I will demonstrate how the interaction of a self-propelling droplet with its chemical field of spent fuel generates swimming and pumping states, unsteady reorientation,  as well as regular helical swimming both individually and collaboratively.