Femtosecond laser preparing patternable liquid-metal-repellent surface for flexible electronics

Hypothesis: Controlling the wetting behaviour of gallium-based liquid metal is highly desired for soft electronics applications. Currently, achieving durable and patternable liquid-metal-repellent surfaces by a simple and flexible method is challenging. The femtosecond laser has a remarkable ability to modify the morphology and wettability of a solid surface. It can also potentially be applied to control the wettability of liquid metal and achieve complete liquid-metal patterns. Experiments: Femtosecond laser processing was used to form a microstructure on a polydimethylsiloxane (PDMS) surface. With regard to the laser-ablated surface, its morphology was observed by a scanning electron microscope, and its wettability to liquid metal was characterized by measuring the contact angle, sliding angle, and adhesive force. Finally, its potential applications in soft electronics were demon-strated. Findings: A layer of micro/nanostructures was directly prepared on the PDMS surface by laser ablation, presenting excellent liquid-metal repellence. Without expensive masks and complex operation processes, programmable liquid-metal-repellent patterns were easily obtained by femtosecond laser selectively treating the PDMS surface, enabling EGaIn to be patterned on the textured surface. The as-prepared liquid-metal patterns can be used as a flexible microheater and a microstrip patch antenna. It is believed that laser-patterned liquid-metal-repellent surfaces will have significant applications in soft electronics, such as antennas, microcircuits, lab on chips, and wearable electronic devices. (C) 2020 Elsevier Inc. All rights reserved.