All-Optical Rapid Formation, Transport, and Sustenance of a Sessile Droplet in a Two-Dimensional Slit with Few-Micrometer Separation

We present a sessile droplet manipulation platform that enables the formation and transport of a droplet on a light-absorbing surface via local laser-beam irradiation. The mechanism relies on solutocapillary Marangoni flow arising from a concentration gradient in a binary mixture liquid. Because the mixture is strongly confined in a two-dimensional slit with a spacing of a few micrometers, the wetting film is stably sustained, enabling the rapid formation, deformation, and transport of a sessile droplet. In addition, to sustain the droplet in the absence of laser irradiation, we developed a method to bridge the droplet between the top and bottom walls of the slit. The bridge is stably sustained because of the hydrophilicity of the slit wall. Splitting and merging of the droplet bridges are also demonstrated.

Automated summary

We introduce a platform for manipulating sessile droplets on a light-absorbing surface using localized laser irradiation. The manipulation is achieved through solutocapillary Marangoni flow caused by a concentration gradient in a binary mixture liquid. The two-dimensional confinement of the mixture enables stable formation, deformation, and transport of the droplet. Additionally, we present a method to sustain the droplet in the absence of laser irradiation by bridging it between the top and bottom walls of a slit.