Formation, Dissolution, and Transfer Dynamics of a Millimeter-Scale Thin Liquid Droplet in Glycine Solution by Laser Trapping

The formation, dissolution, and transfer of a millimeter-scale dense liquid droplet are demonstrated by focusing a CW near-infrared laser beam into a thin film of glycine solution in heavy water. The entire process is investigated by directly monitoring the temporal change in the two-dimensional surface profile using a laser displacement meter. Upon laser irradiation, the surface depression is initially induced by laser heating, followed by the formation of the shallow convex-shaped droplet around the focal spot, in which the droplet is always in contact with the surrounding solution through the ultrathin solution layer. After the laser is switched off, the dissolution occurs through the recovery from the ultrathin layer toward the original solution film. When the laser is set to the outside of the droplet, the solution depression is similarly induced, and subsequently the droplet starts moving toward the focal spot. These processes are summarized and discussed in view of laser-induced effects of concentration increase and temperature elevation.