Printable and Recyclable Conductive Ink Based on a Liquid Metal with Excellent Surface Wettability for Flexible Electronics

Abstract

Flexible electronics greatly facilitate human life due to their convenience and comfortable utilization. Liquid metals are an ideal candidate for flexible devices; however, the high surface tension and poor surface wettability restrict their application on diverse substrates. Herein, a printable and recyclable ink composed of poly­(vinyl alcohol) and a liquid metal (PVA-LM) was developed to resolve these problems. The materials were designed considering the compatibility between PVA and the liquid metal, and the composite theory was applied to determine the component proportion. The developed composites improved the surface wettability of the liquid metal on diverse substrates, and three-dimensional (3D) printing technology was chosen to maximize the use of this material. Moreover, the PVA-LM ink showed excellent conductivity of about 1.3 × 105 S/m after being turned on, which favored the designing of alarm systems and object locators. The flexible sensors produced with this ink have broad application, high sensitivity, and superstable signal generation even after 200 cycles. When acting as strain sensors, the constructed composites had high sensitivity for monitoring the human movements. Furthermore, liquid metals in printed products can be recycled under alkaline conditions. This study opens a new direction for the next generation of environmentally friendly flexible devices.

Multifunctional liquid metal polymer composites

“…(C) Comparison of printing pure liquid metal versus PVA‐LM ink. Reproduced with permission, 156 copyright 2021, American Chemical Society. (D) Images of flower‐shaped pattern screen printed on SIS substrate before (left) and after (right) chemical sintering.…”

Functional liquid metal nanoparticles: synthesis and applications

“…For instance, terephthalate) and polyurethane), exhibit shear thinning behaviors and are recoverable as bulk EGaIn when dissolved in sodium hydroxide. 53 This ink can form functional conductive traces for electronic skins to detect various body movements including pressing, bending, stretching, and even subtle airflows.…”

“…This feature enables LM 4 nanoparticle ink to form high resolution conductive traces printed using different additive manufacturing techniques (i.e., inkjet printing, nozzle dispensing, ballpoint writing) for stretchable and reconfigurable interconnections. 29,[51][52][53][54][55] Despite this, the rigid and insulative oxide interface of LM nanoparticles pose a challenge to create conductive traces. [56][57][58] Several techniques ranging from mechanical, 51,52,59 thermal, 60 and laser-based [61][62][63] activations exist for coalescing the LM nanoparticles.…”

Ga Based Particles, Alloys and Composites: Fabrication and Applications

“…The periodic input voltage generated periodic signal of effective output conductance. Xu et al developed a poly(vinyl alcohol)/LM composite (PVA-LM) with high surface tension and excellent surface wettability on diverse substrates as a printable and recyclable ink for building alarm systems, object locators and electronic skins ( Figure 8 c) [ 91 ]. The alarm system was fabricated by connecting an external power supply, a light-emitting diode and a buzzer with PVA-LM printed circuit, which would be triggered upon pressing, rolling or sweeping the circuit.…”

“…Reproduced with permission. [ 91 ] Copyright 2021, American Chemical Society. ( d ) LED built by LM-polymer composite showing temperature-induced reversible transition between insulator and conductor.…”