Mesoscale-object handling by temperature modulation of surface stresses

In this work, we present the non-contact manipulation of mesoscale random-shaped, large and heavy objects immersed in thin liquid water (< 0.8 mm). The manipulation principle used is the modulation of surface tension by infra red (IR) laser (1480 nm) absorption. Laser absorption generates surface-tension-driven flows. At the water-air interface, the flows go away from the laser beam (colder region), and at the bottom they go toward the laser (recirculation cell). We use these flows to drag immersed objects toward the laser focus. With laser scanning, several kinds of fluidic patterns can be obtained for specific handlings such as trapping, mixing and sorting of microcomponents. High speed flows can be reached; therefore high velocity particle manipulation can be achieved (several mm/s). Experimental measurements reported a velocity of about 5 mm/s for a spherical glass bead of 90 ¿m in diameter. With these flows, nN range forces are obtained. These forces are about 1000 times larger than forces generated with optical tweezers.