Thermocapillary micromanipulation is an emerging non-contact micromanipulation technique, allowing to displace particles in the liquid bulk or at the free surface. When the particles are at the free surface and the surface is heated from the top, the actuation force is repulsive and not attractive. The handling technique is then intrinsically unstable. Therefore, control schemes have been reported recently to deal with this instability. They are based on an experimental characterization of the physical system (depending on the laser, the liquid and the particle properties). In this paper, we explain how we could make use of these handling schemes to estimate the thermocapillary force developed by the laser on the particle to be about 8 nN. This work is a first step towards the handling of multiple particles at the air/liquid interface.

This paper presents a contribution to thermocapillary micromanipulation of floating particles at the free surfaces. Based on a physical model for the so-called capillary dipole interaction, the force between two floating particles is predicted with a Bessel function, whose magnitude can be calculated from the measured distance between particles. This force is then considered as a disturbance force and rejected in the control scheme thanks to a feedforward strategy. We provide theoretical results for this strategy as well as an experimental proof of concept.