Lasers are attractive tools in the framework of non contact micromanipulation. Two different properties are exploited by microrobotic systems: the generated optical forces and the generated heat. The works presented here exploit the generated heat either to move particles.
Non contact actuation based on thermocapillary convection flows
Thermocapillary convection is a promising principle to manipulate particles at the fluid/gas interface. Compared with approaches based on natural and Marangoni convections, our approach uses thermocapillary convection generated by a laser heating the fluid from the top and not from the bottom. This has several advantages, the most relevant being that it does not depend on an hydrodynamic instability to onset the flow motion. Laser heating creates large localized thermal gradients that make the flow velocity fast and localized. Simulations show that flow velocities up to 8.5 mm/s can be obtained using as little power as 38 mW with a temperature increase as little as 4 °C. As a proof of concept, steel spherical particles 20 of 500 μ m diameter are successfully displaced using this principle, which attain a mean maximal speed up to 4 mm/s. Also, 1000-μm-diameter steel spherical particles are displaced along a given trajectory using a manual control. These first results demonstrate the high potential of this new approach based on thermocapillary convection for controlled noncontact actuation at high speeds at microscale. Closed loop control of a single particle has also been demonstrated, as well as the manipulation of a particle in presence of an obstacle.