Electrowetting Assisted Selective Printing of Liquid Metals

The development of soft electronics brings new focus to compliant electronic materials able to withstand high strain in flexible/stretchable devices. Promising candidates for compliant electronic materials are eutectic gallium alloys, which are liquid at room temperature, enabling reconfiguration of their shape without losing conductivity. Many researchers study methods for depositing liquid metal, some using additive manufacturing techniques like direct-write printing to extrude material through a nozzle. We report a new method to enhance this printing, by adding an electrostatic pressure that helps wet the liquid metal to the surface. ElectroWetting Assisted Selective Printing (EWASP) uses an applied voltage between printing nozzle and underlying substrate to control the size and shape of the prints. We demonstrate control of the printed trace width from 50–720 µm by varying the electric field strength. Furthermore, EWASP enables printing on materials that direct-write printing could not, due to poor surface adhesion. The strength of this electrostatic pressure dominates over gravitational forces and allows for printing on vertical surfaces. The gallium oxide shell that forms spontaneously while printing in air holds the traces in their shape once the voltage is removed.