4D‐Printing of Photoswitchable Actuators

Abstract

Shape-switching behavior,w here at ransient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus,iscritical to building smart structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D-print shape-switching liquid crystalline elastomers (LCEs) functionalizedw ith supramolecular crosslinks, dynamic covalent crosslinks,a nd azobenzene.T he salient property of shape-switching LCEs is that light induces longlived, deformation that can be recovered on-demand by heating.U V-light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks,r esulting in ap rogrammed deformation. After UV,t he shapeswitching LCEs fix more than 90 %o ft he deformation over 3daysb yt he reformed supramolecular crosslinks.U sing the shape-switching properties,weprint Braille-like actuators that can be photoswitched to displaydifferent letters.This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.

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

“…Recently, 4D printing was introduced into LCEs in 2017 almost simultaneously by the groups of Ware [ 99 ] and Sanchez-Somolinos [ 11 ] that allows LCEs to achieve more complex and programmable shape changes. Lu et al [ 73 ] designed a novel 4D-printable azobenzene-functionalized LCE material that combined supramolecular crosslinks and dynamic covalent crosslinks (Diels-Alder). After UV irradiation, the programmable shape changes of the materials are stable, which arises from a decoupling of the isomerization.…”

Ultrafast Digital Fabrication of Designable Architectured Liquid Crystalline Elastomer

“…[ 27 ] The utilization of the inherent flow field in extrusion based 3D printing has recently gained attention. [ 28 ] It allows establishing localized domain orientation and overall 3D geometry simultaneously. The process, however, is time‐consuming and the localized orientation is coupled intrinsically to the overall shape.…”

Shape-programmable liquid crystal elastomer structures with arbitrary three-dimensional director fields and geometries

“…Various fabrication techniques have recently been developed to pattern liquid crystals (LCs) into arbitrary 2D inplane director fields, enabling complex 2D to 3D shape transformation. These existing techniques include nano-rubbing with atomic force microscope (AFM) tips 19 , digital micro-mirror device-based photopatterning 20 , plasmonic photopatterning [21][22][23] , pixel-by-pixel photopatterning 11,24 , micro-channels from direct laser writing 12,25 , and 3D printing of dynamic networks 26 . Based on these techniques, various LCE-based stimuli-responsive shapemorphing has been demonstrated, e.g., iris-like device and human face from a flat film 15,27 .…”