4D-Printable Liquid Metal–Liquid Crystal Elastomer Composites

Abstract

Soft actuators that undergo programmable shape change in response to a stimulus are enabling components of future soft robots and other soft machines. Strategies to power these actuators often require the incorporation of rigid, electrically conductive materials into the soft actuator, thus limiting the compliance and shape change of the material. In this study, we develop a 4D-printable composite composed of liquid crystal elastomer (LCE) matrix with dispersed droplets of eutectic gallium indium alloy (EGaIn). Using deformable EGaIn droplets in place of rigid conductive fillers preserves the compliance and shape-morphing properties of the LCE. The process enables 4D-printed LCE actuators capable of photothermal and electrothermal actuation. At low liquid metal (LM) concentrations (71 wt %), the composite actuator exhibits a photothermal response upon irradiation of near-IR light. Printed actuators with a twisted nematic configuration are capable of bending angles of 150° at 800 mW cm–2. At higher LM concentrations (88 wt %), the embedded LM droplets can form percolating networks that conduct electricity and enable electrical Joule heating of the LCE. Actuation strain ranging from 5 to 12% is controlled by the amount of electrical power that is delivered to the composite. We also introduce a method for multimaterial printing of monolithic structures where the LM filler loading is spatially varied. These multifunctional materials exhibit innate responsivity where the actuator behaves as an electrical switch and can report one of two states (on/off). These multiresponsive, 4D-printable composites enable multifunctional, mechanically active structures that can be powered with IR light or low DC voltages.

Toward Application of Liquid Crystalline Elastomer for Smart Robotics: State of the Art and Challenges

“…Coupling the conductive properties and deformability of liquid metal with the reversible deformation of LCEs can be used to fabricate multifunctional electrothermal soft actuators. Ambulo et al [ 100 ] developed a process to fabricate 4D-printable LCEs embedded with liquid metal. The liquid metal provides the LCE composites with electro- and photo-thermal actuation capabilities and is capable of producing 12% deformation (under 1.6 V DC) or 150° bending (under 730 nm NIR light irradiation), respectively.…”

Wearable Actuators: An Overview

“…Carbon nanotubes (CNTs) enable the conversion of near-infrared light to thermal energy while the azobenzene group A44 V6 can trigger the deformation under UV light (Figure 23b). Ware et al exhibited a 4D-printed LM-LCEs which can absorb NIR (730 nm) (Figure 23c) [153]. By the dispersion of Eutectic gallium−indium (EGaIn) in LCE, the composite is 4D-printable to different patterns, achieving up to 150 • bending angle under 800 mw/cm 2 NIR light within 40 s.…”

Wearable Actuators: An Overview

“…Carbon nanotubes (CNTs) enable the conversion of near-infrared light to thermal energy while the azobenzene group A44 V6 can trigger the deformation under UV light (Figure 25b). Ware group exhibited a 4D-printed LM-LCEs which can absorb NIR (730nm) (Figure 25c) [155]. By the dispersion of Eutectic gallium−indium (EGaIn) in LCE, composite is 4D-printable to different patterns, achieving up to 150° bending angle under 800 mw/cm 2 NIR light within 40s.…”