Reprogrammable, Reprocessible, and Self-Healable Liquid Crystal Elastomer with Exchangeable Disulfide Bonds

Abstract

A liquid crystal elastomer (LCE) can be regarded as an integration of mesogenic molecules into a polymer network. The LCE can generate large mechanical actuation when subjected to various external stimuli. Recently, it has been extensively explored to make artificial muscle and multifunctional devices. However, in the commonly adopted two-step crosslinking method for synthesizing monodomain LCEs, the LCE needs to be well-cross-linked in the first step before stretching, which increases the disorder of mesogenic molecules in the final state of the LCE and makes it very challenging to fabricate the LCE of complex shapes. In this article, we developed a new LCE with disulfide bonds, which can be reprogrammed from the polydomain state to the monodomain state either through heating or UV illumination, owing to the rearrangement of the polymer network induced by the metathesis reaction of disulfide bonds. In addition, the newly developed LCE can be easily reprocessed and self-healed by heating. Because of the excellent reprogrammability as well as reprocessability of the LCE, we further fabricated LCE-based active micropillar arrays through robust imprint lithography, which can be hardly achieved using the LCE prepared previously. Finally, we showed an excellent long-term durability of the newly developed LCE.

Siloxane crosslinks with dynamic bond exchange enable shape programming in liquid-crystalline elastomers

“…The first examples of such 'exchangeable LCE' (xLCE) 19 were based on the transesterification bond-exchange reaction (BER), following the original work of Leibler et al 18 In the past few years, a number of strategies based on dynamic covalent bonds to achieve complex alignment in LCEs have been followed, such as disulfide, 20 free-radical addition fragmentation chain transfer, 21,22 exchangeable urethane bonds, 23 and more recently -the boronic transesterification. 24 However, all of these approaches are based on hydrocarbon elastomers and share the problem of continuous creep at a relatively low temperature.…”

Selective Decrosslinking in Liquid Crystal Polymer Actuators for Optical Reconfiguration of Origami and Light‐Fueled Locomotion

“…[2] By controlling the LC alignment (e.g.,uniaxial vs.splayed vs. twisted) or the distribution of crosslinked area, or by using "patterned" stimulation, LCN actuators can realize complex, reversible shape change upon order-disorder phase transitions of the mesogens. [3] Among the important issues on LCN actuators towards practical applications,i st he development of new methodologies that facilitate the preparation of diverse actuators capable of programmable or on-demand shape change and even locomotion using the same liquid crystal polymer (LCP) without the need for organizing the LC alignment in different ways.R ecognizing the importance of chain crosslinking,which memorizes the original LCN shape in ordered phases and enables the actuation reversibility, controlling crosslinking has been the center of attention in many studies.T he most explored strategy is to replace covalent bonds with dynamic covalent bonds for chain crosslinking,byusing transesterification reactions, [4] disulfide metathesis, [5] and exchangeable carbamate bonds, [6] ton ame afew.Inpractical terms,ifanexisting LCN actuator is to be reconfigured to exhibit ad ifferent shape change,i tm ust be reprocessed, generally remoulded by hot-compression, before preparing an ew actuator.A nother reported approach consists in photocrosslinking aligned mesogens in selected areas. [7] Since reversible actuation occurs only in the crosslinked areas,depending on how they are organized, complex shape changes can be achieved.…”

Advances in Cell Scaffolds for Tissue Engineering: The Value of Liquid Crystalline Elastomers

“…In fact, this light source can trigger a disulfide exchange reaction resulting in the rearrangement of the crosslinked networks. The same concept was applied to demonstrate the self‐healing capability of the material …”

“…The same concept was applied to demonstrate the self-healing capability of the material. [41] Amines have also been used for Michael addition with the same diacrylate LCs. In this strategy,t he amine works as a chain extenderdue to adouble addition on the same nitrogen, formingo ligomers with terminal acrylate group.…”