Tough and Photo-Plastic Liquid Crystal Elastomer with a 2-Fold Dynamic Linker for Artificial Muscles

Dynamic Programme Locking of Isomerization Behavior of Molecular Switch in Liquid Crystal Elastomers

The reversible isomerization behavior of molecular switches in liquid crystal elastomers (LCEs) usually only can be monotonically repeated, because the molecular motion environment is the same for each isomerization cycle in a permanently cross-linked polymer network. Therefore, achieving a tunable photostationary state (PSS) in the same LCE material system is a significant challenge. Herein, a spiropyran-based material (SPBM) as the molecular switch is introduced into a LCE system, which constructed a typical photo-responsive material with reversible isomerization behavior. Furthermore, dynamic cross-linked polymer networks via diselenide bonds endow the SPBM in this system with a tunable molecular motion environment, which switches freely or restrictedly depending on the size of the free volume. Thus, the molecular switch can endow the LCE with programmable photo-response, and a program locking or unlocking is enabled by tuning the free volume. This post-programming locking (PPL) strategy may offer a new sight for promoting the higher controllability of the stimulus-responsive behavior of the smart materials.

Programmable, Self-Healable, and Photochromic Liquid Crystal Elastomers Based on Dynamic Hindered Urea Bonds for Biomimetic Flowers

Recently, researchers have been exploring the use of dynamic covalent bonds (DCBs) in the construction of exchangeable liquid crystal elastomers (LCEs) for biomimetic actuators and devices. However, a significant challenge remains in achieving LCEs with both excellent dynamic properties and superior mechanical strength and stability. In this study, a diacrylate-functionalized monomer containing dynamic hindered urea bonds (DA-HUB) is employed to prepare exchangeable LCEs through a self-catalytic Michael addition reaction. By incorporating DA-HUB, the LCE system benefits from DCBs and hydrogen bonding, leading to materials with high mechanical strength and a range of dynamic properties such as programmability, self-healing, and recyclability. Leveraging these characteristics, bilayer LCE actuators with controlled reversible thermal deformation and outstanding dimensional stability are successfully fabricated using a simple welding method. Moreover, a biomimetic triangular plum, inspired by the blooming of flowers, is created to showcase reversible color and shape changes triggered by light and heat. This innovative approach opens new possibilities for the development of biomimetic and smart actuators and devices with multiple functionalities.

Coiled Carbon Nanotube Fibers Sheathed by a Reinforced Liquid Crystal Elastomer for Strong and Programmable Artificial Muscles

Fibers of liquid crystal elastomers (LCEs) as promising artificial muscle show ultralarge and reversible contractile strokes. However, the contractile force is limited by the poor mechanical properties of the LCE fibers. Herein, we report high-strength LCE fibers by introducing a secondary network into the single-network LCE. The double-network LCE (DNLCE) shows considerable improvements in tensile strength (313.9%) and maximum actuation stress (342.8%) compared to pristine LCE. To facilitate the controllability and application, a coiled artificial muscle fiber consisting of DNLCE-coated carbon nanotube (CNT) fiber is prepared. When electrothermally driven, the artificial muscle fiber outputs a high actuation performance and programmable actuation. Furthermore, by knitting the artificial muscle fibers into origami structures, an intelligent gripper and crawling inchworm robot have been demonstrated. These demonstrations provide promising application scenarios for advanced intelligent systems in the future.

Tunable and Switchable Thermochromism in Cholesteric Liquid Crystalline Elastomers

Thermochromic materials have found widespread commercial use in packaging as temperature indicators. Often, these products utilize leuco dyes that are mixed into conventional polymeric resins to prepare coatings or films that exhibit temperature-dependent color change. Here, we consider a distinctive approach to thermochromism via the selective reflection of liquid crystalline elastomers that retain the helicoidal structure of the cholesteric phase (CLCEs). Upon heating, the order of the CLCEs reduces and approaches zero, resulting in a change in birefringence as well as material thickness, both of which manifest as changes in the selective reflection to heating. This examination systematically prepares CLCEs capable of reversible thermochromic response as a function of cross-link density and liquid crystalline composition. A particular focus of this examination is the preparation of CLCEs composed of chiral and achiral liquid crystalline monomers that reduce the strength of the mesogen-mesogen interaction and accordingly reduce the nematic-isotropic transition temperature. The low birefringence of some of the CLCE compositions facilitates thermochromic reflection tuning, followed by switching.