Optical adhesion of photocurable emulsion droplets using laser trapping

Abstract

As represented by "Lab on a Tip" using microchannels, the miniaturization of manufacturing and inspection processes attracts widespread interest. Therefore, many micro-tool fabrication techniques using optical tweezers have been reported. Most reported methods focus on assembling trapped microbeads, and it was necessary to have a photocurable resin phase and surface modification process to assemble solid beads. However, because many procedures such as dispersion of microbeads and removal from the resin solution were required, flexible one-step fabrication is difficult with previous methods. This study proposed a direct adhesion and assembly of the photocurable resin droplets dispersed in the aqueous solution. Since the photocurable droplets work as both base material and an adhesive, a flexible one-step fabrication of micro-tools can be achieved. It was experimentally found that the morphology of emulsion droplets in contact significantly affects the adhesion. Generally, oil-in-water emulsion droplets are stabilized by a surfactant, and adhesion between droplets can be disturbed by a surfactant bilayer. By controlling the contact angle between the droplets, the optically trapped droplets successfully adhered together with photopolymerization. Furthermore, combining the various diameter and materials of emulsion droplets using microfluidic channels, more functional and complex microtools can be expected.