Abstract

Laplace Pressure Tuned Liquid-Metal Non-Spherical Micro-Droplet (Plug) Generator

Sagar Bhagwat, Ph.D. Student , Albert-Ludwigs-University of Freiburg, Department of Microsystems Engineering (IMTEK)

Gallium-based liquid metal non-spherical droplets (plugs) are fascinating materials owing to their exceptionally high surface tension (~600-700 mN m-1), low viscosity (twice that of water), negligible vapor pressure and high electrical conductivity (~3.4 × 106 S m-1), and have seen applications in microfluidics, microelectromechanical systems (MEMS), micro-actuators, switches, valves, radio-frequency and reconfigurable devices, and sensor technology. Typically, flow-focusing devices or manual injection inside narrow channels are the techniques used to generate liquid metal plugs. However, plug size control and reproducibility of the plugs is a major challenge hampering the use of such plugs. We developed a plug generator with a channel which includes chambers and constrictions that are optimally designed by tuning their respective Laplace pressures. We show that by having a chamber with lower Laplace pressure compared to a constriction exerting higher Laplace pressure, the liquid metal will be forced to fill the chamber than the constriction. We further presented liquid metal plugs of various aspect ratios for channel widths of 0.5, 0.8 and 1 mm with constriction width of 0.1 mm. This method allows control over liquid-metal plug size, reproducibility and provides a reliable way to generate plugs directly on-chip and on-demand for microfluidic applications.