Liquid Crystal Elastomer with Integrated Soft Thermoelectrics for Shape Memory Actuation and Energy Harvesting

Abstract

Liquid crystal elastomers (LCEs) have attracted tremendous interest as actuators for soft robotics due to their mechanical and shape memory properties. However, LCE actuators typically respond to thermal stimulation through active Joule heating and passive cooling, which make them difficult to control. In this work, LCEs are combined with soft, stretchable thermoelectrics to create transducers capable of electrically controlled actuation, active cooling, and thermal‐to‐electrical energy conversion. The thermoelectric layers are composed of semiconductors embedded within a 3D printed elastomer matrix and wired together with eutectic gallium–indium (EGaIn) liquid metal interconnects. This layer is covered on both sides with LCE, which alternately heats and cools to achieve cyclical bending actuation in response to voltage‐controlled Peltier activation. Moreover, the thermoelectric layer can harvest energy from thermal gradients between the two LCE layers through the Seebeck effect, allowing for regenerative energy harvesting. As demonstrations, first, closed‐loop control of the transducer is performed to rapidly track a changing actuator position. Second, a soft robotic walker that is capable of walking toward a heat source and harvesting energy is introduced. Lastly, phototropic‐inspired autonomous deflection of the limbs toward a heat source is shown, demonstrating an additional method to increase energy recuperation efficiency for soft systems.

Printing Liquid Metal Elastomer Composites for High‐Performance Stretchable Thermoelectric Generators

“…[ 30 ] Most recently developed TEGs with similar device architecture but significantly higher fill factor (28%) show a maximum power density of 236 µW cm –2 at this temperature gradient. [ 55 ] Regardless of having a 50% lower fill factor, the power density of our printed TEGs is 2.75 times that of these flexible TEGs under the same condition. This superior energy harvesting performance holds true even at lower temperature gradients.…”

3D Printing of Liquid Metal Embedded Elastomers for Soft Thermal and Electrical Materials

“…Demonstration of Active Cooling on Wearable Peltier Cooling Device. A wearable wrist worn garment-like Peltier device for limb cooling based on work by Zadan et al 11,29 is fabricated with a 6 × 15 array of doped p-and n-type Bi2Te3 semiconductors (Wuhan Xinrong New Materials Co., Ltd.) with a purity of 99.99%. The semiconductors were placed alternatingly with the n-/p-types in series into a 3D printed polymer center.…”

“…Using this printing framework, we can create a variety of 3D structures and LMEE-based soft-matter devices . Furthermore, we demonstrate the ability to use 3D printing to improve the performance of functional LMEE interfaces used for a soft and stretchable triboelectric nanogenerator (TENG) and thermoelectric device (TED) . We have previously shown the ability to use LMEEs for TENGs and TEDs capable of generating electricity from body motion and heat, respectively.…”

“…3 Furthermore, we demonstrate the ability to use 3D printing to improve the performance of functional LMEE interfaces used for a soft and stretchable triboelectric nanogenerator (TENG) 12 and thermoelectric device (TED). 29 We have previously shown the ability to use LMEEs for TENGs 12 and TEDs 11 capable of generating electricity from body motion and heat, respectively. However, those applications used flat sheets of LMEEs that lacked the 3D architectures needed to maximum triboelectric charging and convective heat flow.…”

Recent advances in molecular programming of liquid crystal elastomers with additive manufacturing for 4D printing

“…Another roadblock to reducing LCE transformation cycle time is that deactivation of LCEs is typically done by natural cooling. 95 Although there are still remaining challenges and technical obstacles, additive manufacturing of LCEs is specifically gaining ground as next generation 4D printing because of the advantages of LCEs over SMPs and hydrogels. We believe that the recent advances in additive manufacturing and materials development of LCEs will stimulate further exploration of new mesogen alignment techniques, innovative approaches to achieve molecular orders during AM process, and a broad spectrum of LCE applications.…”