Formation of Spherical and Non-Spherical Eutectic Gallium-Indium Liquid-Metal Microdroplets in Microfluidic Channels at Room Temperature

Abstract

Here, the formation of eutectic Gallium-Indium (EGaIn) liquid-metal microdroplets, both spherical and non-spherical, in microfluidic devices at room temperature is reported. Monodisperse microdroplets were created in an aqueous polyethylene glycol (PEG) solution, in oxygenated and in deoxygenated silicone oil. The volume of the droplets depends on the channel dimensions and flow rates applied, varying between 0.5 and 4 nL. Non-spherical droplets were formed in oxygenated silicone oil due to the instantaneous formation of an oxide layer. These metal “micro-rice” droplets retained their shape and did not spontaneously reflow to form shapes of the lowest interfacial energy on egress from the channel, unlike in aqueous PEG solution and in deoxygenated silicone oil. Liquid-metal droplets with such tunable morphology can potentially be used in MEMS devices for optical and electrical switches, valves and micropumps.