Abstract

Interfaces affect the motion of micro-swimmers in interesting ways, owing to the boundary conditions that they enforce on the fluid flow caused by the swimmer. In this talk, I will present my research on the modelling and analysis of micro-swimmer motion near fluid-fluid and fluid-solid interfaces.

In a first part, we will see how ‘hydrodynamic trapping’ of model micro-swimmers around spherical obstacles (e.g., oil drops) is fundamentally altered by surfactant-induced interfacial effects. On a related note, we will also discuss the dynamics of microorganisms in an asymmetric confinement: an air-liquid interface on one side and a liquid-liquid interface on the other, and highlight the utility of far-field hydrodynamic models in predicting swimming behaviour near interfaces.

In a second part, we will move to studying active drops: physico-chemically symmetric entities that convert chemical energy from their surroundings to spontaneous mechanical motion, via self-sustained surface flows. These drops typically evolve near rigid walls yet existing theories neglect this effect of confinement on the analysis of drop motion. Through numerical simulations, I will provide physical insights into the influence of wall proximity on the motion of active drops along the wall. Specifically, I will explain why reduced drop-wall separations actually promote the drop’s self-propulsion.