Directed Assembly of Liquid Metal–Elastomer Conductors for Stretchable and Self‐Healing Electronics

Abstract

Due to the growing interest in soft robotics, stretchable electronics, and electronic skins, there is demand for compliant electrodes and interconnects that are soft, stretchable and conductive.Here, we use dielectrophoresis (DEP) to assemble, align, and sinter microdroplets of liquid metal-eutectic Ga-In (EGaIn)-in uncured polydimethylsiloxane (PDMS) to form electrically conducting microwires. There are several noteworthy aspects of this approach: (1) Generally, liquid metal droplets in silicone at loadings approaching 90 wt% remain insulating and form conductive network only when subjected to sintering. Here the use of DEP facilitates assembly of the filler droplets into conductive microwires at loadings as low as 10 wt% EGaIn. (2) Dielectrophoresis is done in silicone for the first time, enabling the microwires to be cured in a stretchable matrix. (3) Because the droplets are liquid, they sinter during dielectrophoresis to form a stretchable metallic microwire that retains its shape after curing the silicone and does not change resistance during mechanical strain. (4) The use of liquid metal eliminates the issue of compliance mismatch observed in soft polymers with solid fillers. (5) The silicone-EGaIn "ink" can be placed in holes created by severely damaged regions of stretchable wires to create stretchable interconnects that heal the damage both mechanically and electrically. We characterize the DEP process of this unique set of materials and demonstrate the interesting attributes enabled by such liquid microwires.

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

“…We highlight here the importance of sheath-core design for fabricating LM microfibers; without the protection of the fluoroelastomer sheath, LM leakage may easily occur (fig. S4), which has increasingly become an issue that has to be faced in the practical uses of LM composite materials ( 40 ). Furthermore, to improve the toughness and elastic recovery of the LM sheath-core fiber ( 41 ), we introduced a second covalent network in the sheath by post–ultraviolet-polymerizing the added difunctional monomers, PEGDA ( M n : 250 g/mol), in the middle spinning solution.…”

Pervasive liquid metal printed electronics: From concept incubation to industry

“…Currently, successfully doped metal particles have included Cu, Ag ( Tang et al., 2017 ), Fe ( Cao et al., 2020 ; Carle et al., 2017 ; Hu et al., 2019 ), Ni ( Chang et al., 2018 ; Guo et al., 2018c ), Mg ( Wang et al., 2018c ), W ( Kong et al., 2019 ), etc. Further, based on more generalized liquid metal composite strategy ( Chen et al., 2020 ), the liquid metal dispersed into micro-nano droplets can form liquid metal-polymer composites with the polymer ( Chechetka et al., 2017 ; Fassler and Majidi, 2015 ; Krisnadi et al., 2020 ; Li et al., 2018 , 2020 ; Peng et al., 2019 ; Tang et al., 2018 ; Wang et al., 2018b ), and the resulting ink can be flexibly applied to different substrates ( Figure 2 B). But because of the dispersed liquid metal droplets, special treatments to make them conductive are usually necessary, such as laser ( Deng and Cheng, 2019 ; Liu et al., 2018a ), low temperature ( Chen et al., 2019 ; Wang et al., 2019 ), mechanical pressure ( Boley et al., 2015 ; Zhang et al., 2019a ), evaporation ( Li et al., 2019b ), in situ reduction of silver shell ( Zheng et al., 2020 ), and stretch ( Thrasher et al., 2019 ; Xin et al, 2019 ).…”

Morphological Hydrogel Microfibers with MXene Encapsulation for Electronic Skin

“…Benefiting from dramatic progresses on the study of stretchable electronics, electronic skins have attracted considerable interests to both commercial development and the research community due to their potential applications in artificial intelligence systems [4,5], wearable health monitoring [6,7], human-machine interface [8,9], and other fields [10][11][12]. Nowadays, numerous electrical conductors, including ionic liquids [13,14], liquid metals [15,16], and other two-dimensional materials [17][18][19], have been integrated with stretchable sheets to respond to external stimuli and transmit corresponding electrical signals. Among those electrical conductors, MXenes [20,21], as one class of two-dimensional early-transition metal carbides/carbonitrides, have emerged with widespread attention due to their fascinating properties, such as large hydrophilic surfaces and excellent electrical/thermal conductivity.…”