Flexible Finely and Directly Patternable Liquid Metal Electrodes via Selective Surface Wetting Technique

Abstract

Eutectic gallium–indium (EGaIn) is an ideal material for preparing flexible electrodes, but its high surface tension poses a challenge during deposition and patterning. Herein, we propose a laser-induced selective surface wetting technique (SSWT) to enable the facile and straightforward fabrication of flexible finely and directly patternable EGaIn liquid metal electrodes. Our proposed technique selectively controls the wettability of EGaIn by establishing a perfluorinated self-assembled monolayer on a zinc oxide nanorod array to impart superhydrophobicity and then inducing specific sites on the hydrophilized surface by ultraviolet (UV) pulsed laser ablation, thereby enabling fine patterning (linewidth, ~50 μm). Surface analysis of the effect of laser ablation was also performed to elucidate the mechanism of SSWT. The patterned EGaIn liquid metal electrode fabricated by SSWT exhibited superior flexibility, with a resistance change (ΔR/R0) of only 18.6% compared with a Ag thin film electrode, which showed a dramatic increase in ΔR/R0 to nearly 500% after 50,000 folding cycles at a peak strain of 2.5%. The simple and easily implementable liquid metal patterning technique proposed in this study may potentially be applied in the field of wearable and stretchable electronics, which requires extreme flexibility.