Electrowetting‐Assisted Selective Printing of Liquid Metal

The use of electrowetting‐on‐dielectric to enhance liquid metal extrusion printing is reported. Electrowetting facilitates the controlled deposition of gallium alloys on any substrate, specifically those relevant to radio‐frequency (RF) electronics and other “non‐stick” surfaces. To enhance adhesion on these surfaces, electric fields are applied between liquid metal and an underlying substrate electrode during extrusion. This process, termed as electrowetting‐assisted selective printing (EWASP), allows digital control of the printing process by toggling the voltage, as well as analog control by tuning the amplitude of the applied voltage. EWASP improves the control of the printing process by increasing both the range and selectivity of trace widths, allowing printing on omni‐phobic surfaces, vertically oriented features, and printing liquid metal directly into a prepolymer matrix. Gallium‐based liquid metals such as eutectic gallium–indium (EGaIn) form an oxide shell which structurally secures the printed metal's shape once voltage is removed. EWASP enables the pattern definition of stable‐printed liquid metal features defined by an underlying electrode and the subsequent transfer to another substrate or encapsulation within elastomers. Pattern transfer is demonstrated by both serial extrusion over electrode features and by a parallel dip‐coating process where the substrate is immersed in liquid metal and extracted with voltage applied, replicating the electrode features in liquid metal.