Fuel-free light-driven colloidal swimmers

Conventional artificial active swimmers use chemical fuel to propel themselves. We present swimmers made by an oil droplet partially wetting a black dynabead that use no chemical fuel and are driven solely by light. The black dynabead absorbs light and provides a temperature gradient responsible for the motion of the swimmer. A thin-film resistive heater which acts as its own thermometer is used as a local heat source in order to characterize the motion and probe the mechanism, Marangoni or thermophoresis, for propulsion. As expected we observe motility-induced phase separation in dense colonies of these swimmers. We show that interactions between individual swimmers are non-reciprocal and orientation dependent.