Soft and Stretchable Liquid Metal Composites with Shape Memory and Healable Conductivity

Abstract

Shape memory composites are fascinating materials with the ability to preserve deformed shapes that recover when triggered by certain external stimuli. Although elastomers are not inherently shape memory materials, the inclusion of phase-change materials within the elastomer can impart shape memory properties. When this filler changes the phase from liquid to solid, the effective modulus of the polymer increases significantly, enabling stiffness tuning. Using gallium, a metal with a low melting point (29.8 °C), it is possible to create elastomeric materials with metallic conductivity and shape memory properties. This concept has been used previously in core–shell (gallium-elastomer) fibers and foams, but here, we show that it can also be implemented in elastomeric films containing microchannels. Such microchannels are appealing because it is possible to control the geometry of the filler and create metallically conductive circuits. Stretching the solidified metal fractures the fillers; however, they can heal by body heat to restore conductivity. Such conductive, shape memory sheets with healable conductivity may find applications in stretchable electronics and soft robotics.

A Data‐Driven Review of Soft Robotics

“…[ 513 ] These works represent common uses seen in the analyzed publications, and new recipes and applications of various shape‐memory materials are still being explored. [ 514–516 ]…”

Liquid Metal Patterned Stretchable and Soft Capacitive Sensor with Enhanced Dielectric Property Enabled by Graphite Nanofiber Fillers

“…Gallium based liquid metals, especially EGaIn, have attracted great interest as conducting elements for application in soft and stretchable electronics due to their remarkable properties such as "infinite" stretchability, metallic conductivity, and fluidity near room temperature [32,34,[79][80][81][82][83]. In a liquid state, they can easily be injected or vacuum filled into microchannels, capillaries, and tubing under appropriate dimensional and pressure conditions or can be patterned on surface of substrates by various unorthodox non-lithograpic methods such as direct writing, stencil printing, and magnetic field guided patterning by formation of liquid metal inks [31,79,80,84]. EGaIn spontaneously forms a passivating oxide layer in air which is responsible for notoriously adhering to most substrates [85].…”

“…In lieu of them, gallium based liquid metal alloys can be utilized as soft and stretchable electrodes. Gallium and its alloys have drawn tremendous attention in the field of stretchable electronics due to their metallic conductivity, fluidity, and reconfigurability [31][32][33][34][35]. Previously, the liquid metals have been rheologically modified to make conductive pastes to serve various purposes such as conductive inks for printed stretchable circuit boards and soft 3D conductive structures [36][37][38].…”

Ga Based Particles, Alloys and Composites: Fabrication and Applications

“…It was worth mentioning that the temperature to trigger the electrical transition was about 212 K, at which point the resistivity value suddenly changed by more than nine orders of magnitude. Recently, Bhuyan et al synthesized an elastomeric material with metallic conductivity and shape memory properties by injecting Ga into soft silicone microchannels (Figure 8e) [97]. On one hand, as a phase-change material, the rigidity of Ga helped the polymer to hold its programmed shape and store elastic energy in the external silicone matrix at the room temperature.…”

“…[96] Copyright 2019, Wiley-VCH. (e) Schematic illustration of soft and stretchable LM composites with thermal-induced shape memory and healable conductivity.Reproduced with permission [97]. Copyright 2021, American Chemical Society.…”