Ultra-conformable Liquid Metal Particle Monolayer on Air/water Interface for Substrate-free E-tattoo

TL;DR

This paper introduces a novel multi-size self-assembly method for creating large-area, ultra-conformable liquid metal monolayers at air/water interfaces, enabling substrate-free flexible e-tattoos with high stability and transferability.

Contribution

It develops a simple z-axis undisturbed interfacial strategy for stable, large-area liquid metal monolayers, overcoming gravity-related assembly challenges.

Findings

Achieved large-area (>100 cm²) liquid metal monolayers with high floating yield (50-90%).

Enabled transfer of liquid metal films onto complex surfaces like skin and leaves.

Demonstrated substrate-free, conformal liquid metal e-tattoos for continuous monitoring.

Abstract

Gallium-based liquid metal is getting increased attention in conformal flexible electronics for its high electrical conductivity, intrinsic deformability and biocompatibility. A series of flexible devices are developed based on the micro-particles of liquid metal. But it is still challenging to fabricate conformal liquid metal film with a large area and high uniformity. Interfacial self-assembly is a competitive candidate method. Traditional interfacial self-assembly methods have difficulties assembling liquid metal particles because the floating state of the high-density microparticles could be easily disturbed by gravity. Here, we realized the multi-size universal self-assembly (MUS) for liquid metal particles with various diameters (0~500{\mu}m). By introducing a simple z-axis undisturbed interfacial material releasing strategy, the interference of gravitational energy on the stability of floating particles is avoided. Benefits from this, the ultra-conformable monolayer film, with large area (>100 cm2) and high floating yield (50%~90%), can be fabricated by liquid metal particles. Furthermore, the monolayer can be conformally transferred to any interesting complex surface such as human skin and plant leaf, to fabricate substrate-free flexible devices. Without interference from the mechanical response of traditional substrate, the liquid metal e-tattoo is more user-friendly and can realize feel-less continuous monitoring.