Liquid Metal Repellency By Nanoporous Films

Gallium (Ga) and its liquid alloys are promising alternatives to toxic mercury (Hg) for use in microfluidics, soft and conformal electrodes, and stretchable electronic devices. This family of alloys is liquid at room temperature (viscosity ~2x of water), possess virtually no vapor pressure and display high conductivity (~1/16 of copper).  However, Ga and its alloys spontaneously form a surface oxide, which dominates its rheological behavior. In addition, this oxide layer adheres to most surfaces and poses a challenge for reconfigurable metallic structures.  To prevent adhesion, current methods use acid-treatment or an interfacial slip layer of water. This work investigates the use of non-wetting nanoporous structures to prevent adhesion of Ga oxide. We examine the EGaIn interface with these structures using contact-angle goniometry and inverted optical microscopy. We also demonstrate reversible actuation of EGaIn on non-wetting surfaces by pneumatics and low voltages.