Liquid Crystal Elastomers in Soft Robotics

Reconfigurable liquid crystal elastomers use pixel-based director patterns for multi-mode shape morphing in soft robotics and adaptive surfaces.

LCEs are monolithic materials that exhibit programmable, three-dimensional (3D) shape morphing. Multi-mode shape morphing of LCEs is in high demand but difficult to achieve. After configuring the LCE director patterns, reconfiguration is generally not possible. Novel research has demonstrated the ability to assemble and disassemble LCE pixels, enabling manual reconfiguration. This approach demonstrates multi-mode shape morphing in LCEs, enabling broader LCE applications in fields such as soft robotics.

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Reconfiguring Shape Morphing Modes

Researchers fabricated LCE films with planar alignment on the bottom surface and perpendicular alignment on the top surface. This splay alignment enabled simple pixel assembly and the design of the shape-morphing mode. Then, they cut the LCE film along the design orientations. Next, the researchers used UV glue to reassemble the pixels into an LCE film with designed director patterns.

The researchers assembled LCE films with pixels of varying geometries. This allowed them to investigate the effect of pixel size and shape on LCE shape morphing. Temperature change is one method to evoke the shape morphing behavior of LCEs. In this study, researchers heated the film to 30 °C, 60 °C, and 90 °C.

After heating the LCEs and observing their behavior, the researchers cut the LCE film into their original pixels. Then, they re-assembled them into a new film with a different director pattern. By reconfiguring the initial shapes and the director patterns, they could design shape morphing modes.

Shapes for Soft Robotics

This reconfiguration strategy shows the functionality of LCE-based soft robotics. For example, researchers fabricated a nine-pixel structure with a 𝛼=0° director field in the shape of a stripe. When heated to 40 °C, the strip transformed into a circle. At 60 °C, it transformed into a helix. Then, the researchers disassembled it into a cross shape, which, when heated, could function as a gripper. These two functionalities have direct applications in soft robotics. In soft robotics, helix shapes allow for locomotion, and grippers for grabbing. Thus, this reconfiguration strategy may lead to increased functionality of LCE-based soft robotics.

Future of Multi-Mode Shape Morphing LCEs

Theoretically, the reconfiguration of these LCE director patterns and initial shapes could occur for an unlimited number of times. One barrier found in this study is the type of glue used to assemble the LCEs. The glue was not removable after de-assembly of the LCE films, leading to a buildup of glue. Coupling this method with a reversible glue could increase the applicability of this technology.