Closed-Loop Particle Motion Control Using Laser-Induced Thermocapillary Convective Flows at the Fluid/Gas Interface at Micrometric Scale

Noncontact actuation has gained a large interest over the last few years, and many works have been performed on magnetic actuation, dielectrophoresis, or optical tweezers. Thermocapillary convective flows are an attractive alternative to manipulate micrometric scale particles at the water/air interface. These flows are generated when a surface tension stress is generated at the fluid/gas interface due to a thermal gradient. Laser heating allows to generate fast, localized flows that improve the actuation performance. In this paper, a closed-loop controller is used to control the particle motion. To design this controller, a model for the system is proposed and experimentally identified. Proof of concept experiments are performed using a 500-μm-diameter steel spherical particle that show that the particle can be successfully displaced towards a target position. Experimental results show that maximal particle velocities between 4-9 mm/s can be attained during the control phase, which can be compared against some of the fastest actuation principles that use Marangoni effect.