Thermocapillary microswimmers: translational propulsion of illuminated particles at a fluid interface

At a fluid interface, thermocapillary forces cause motion of heated asymmetrical micron sized particles. The forces are a consequence of the Marangoni effect, which is caused by the dependence of the surface tension on temperature. For a microgear of an asymmetric shape, a net torque is exerted on the particle, causing it to rotate linearly with the illumination power. In the past, such self-propelled microgears have been strongly investigated.

However, to our knowledge, no corresponding translational motion has ever been investigated. In this presentation, we show that the aforementioned phenomenon can also be exploited for translational propulsion of micron particles. Therefore, we present a numerical model that couples the transient (Navier-)Stokes equation with heat transfer and a moving mesh feature. Different particle shapes and parameters influencing the propulsion speed are examined. We identify the favourable parameters for propulsion speed and determine the scale on which a thermocapillary propulsion of particles at fluid interfaces is possible.