Programming Liquid Crystalline Elastomer Networks with Dynamic Covalent Bonds

Abstract

A liquid crystalline elastomer (LCE) network consisting of dynamic covalent bonds (DCBs) is referred as a LCE vitrimer. The mesogen alignment and the network topology can be reprogrammed locally in the LCE vitrimer by activating the bond exchange reactions using an external stimulus. After removal of the external stress, a new network is formed and the reprogrammed shape can be fixed, leading to a different set of the physical properties of the LCE vitrimers. Herein, this type of emerging materials is reviewed by a brief introduction of the fundamentals of LCEs, followed by discussions of various DCBs and the design principles for LCE vitrimers. After a presentation of different strategies to improve the stability and reprogrammability of the registered mesogen alignment, approaches to prepare LCE vitrimers with complex shapes and their actuations are discussed. Potential applications such as self‐healing and recycling, mechanochromic effects, and post‐functionalization of nanopores are also reviewed, followed by the conclusion of the remaining challenges and opportunities.

Network Topology Optimization for Alignment Programming of a Dynamic Liquid Crystalline Organo-Gel

“…Combining the two different approaches, we can diversify the actuation behaviors. We believe this work is helpful in the design of LCE-based actuators. , …”

“…We believe this work is helpful in the design of LCE-based actuators. 28,29 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Exploiting Molecular Orders at the Interface of Microdroplets for Intelligent Materials

“…LC molecules can be aligned in order below the nematic to isotropic transition temperature ( T NI ). LCs with reactive end groups such as acrylate, often referred to as reactive mesogenic monomers (RMs) or LC oligomers (LCOs), can be cross-linked with chain extenders into soft networks, liquid crystalline elastomers (LCEs). , When heated above T NI , the LC mesogens undergo a transition from the aligned state (the nematic phase) to the disordered isotropic state, exerting substantial anisotropic stress on the network that causes anisotropic shape change, that is, shrinkage in the aligned direction and expansion in the perpendicular directions. Such responses of LCEs are exploited for applications spanning from biosensors to soft actuators. − Since the change in physical properties is highly dependent on the intrinsic molecular order of the LC mesogens, there have been substantial efforts to develop new methods to program the molecular order …”

Liquid crystalline elastomer self-oscillating fiber actuators fabricated from soft tubular molds

“…The coupling between the liquid crystal orientation and crosslinked network elasticity can induce large, reversible anisotropic shape changes in response to external stimuli. 45–50 Patterning the molecular alignment into crosslinked networks can lead to diverse shape morphing forms of LCEs or LCNs and thus allow for the creation of the desired motion mode, including self-oscillation. 12–26 Traditional LCE or LCN light-propelled self-oscillators are often processed into strip-like geometries or cantilever types, and self-oscillations are triggered by alternate photoactivation of the two surfaces during cyclic motions of inertial bending and unbending.…”