Liquid crystal elastomers (LCEs) are broadly recognized as programmable actuating materials that are responsive to external stimuli, typically heat or light. Yet, soft LCEs that respond to changes in environmental humidity are not reported, except a few examples based on rigid liquid crystal networks with limited processing. Herein, a new class of highly deformable hygroscopic LCE actuators that can be prepared by versatile processing methods, including surface alignment as well as 3D printing is presented. The dimethylamino‐functionalized LCE is prepared by the aza‐Michael addition reaction between a reactive LC monomer and N,N′‐dimethylethylenediamine as a chain extender, followed by photopolymerization. The humidity‐responsive properties are introduced by activating one of the LCE surfaces with an acidic solution, which generates cations on the surface and provides asymmetric hydrophilicity to the LCE. The resulting humidity‐responsive LCE undergoes programmed and reversible hygroscopic actuation, and its shape transformation can be directed by the cut angle with respect to a nematic director or by localizing activation regions in the LCE. Most importantly, various hygroscopic LCE actuators, including (porous) bilayers, a flower, a concentric square array, and a soft gripper, are successfully fabricated by using LC inks in UV‐assisted direct‐ink‐writing‐based 3D printing.

Artificial muscles are indispensable components for next-generation robotics capable of mimicking sophisticated movements of living systems. However, an optimal combination of actuation parameters, including strain, stress, energy density and high mechanical strength, is required for their practical applications. Here we report mammalian-skeletal-muscle-inspired single fibres and bundles with large and strong contractive actuation. The use of exfoliated graphene fillers within a uniaxial liquid crystalline matrix enables photothermal actuation with large work capacity and rapid response. Moreover, the reversible percolation of graphene fillers induced by the thermodynamic conformational transition of mesoscale structures can be in situ monitored by electrical switching. Such a dynamic percolation behaviour effectively strengthens the mechanical properties of the actuator fibres, particularly in the contracted actuation state, enabling mammalian-muscle-like reliable reversible actuation. Taking advantage of a mechanically compliant fibre structure, smart actuators are readily integrated into strong bundles as well as high-power soft robotics with light-driven remote control.

Despite many efforts in structuring surfaces using mechanical instabilities, the practical application of these structures to advanced devices remains a challenging task due to the limited capability to control the local morphology. A platform that programs the orientation of mechanically anisotropic molecules is demonstrated; thus, the surface wrinkles, promoted by such instabilities, can be patterned in the desired manner. The optics based on a spatial light modulator assembles wrinkle pixels of a notably small dimension over a large area at fast fabrication speed. Furthermore, these pixelated wrinkles can be formed on curved geometries. The pixelated wrinkles can record images, which are naturally invisible, by mapping the gray level to the orientation of wrinkles. They can retrieve those images using the patterned optical phase retardation generated under the crossed polarizers. As a result, it is shown that the pixelated wrinkles enable new applications in optics such as image storage, informative labeling, and anti‐counterfeiting.

A facile method for fabricating 3D-shaped liquid crystal elastomers at the macro- and microscales was developed by mechanical programming coupled with two-step photocrosslinking.

Poly(β-amino esters) (PBAEs), which include tertiary amines at the β-position of ester linkages, are promising in biomaterials due to their biodegradability and pH responsiveness. Such characteristics in the molecular structure are also appealing for designing catalyst-free covalent adaptable networks (CANs), but this has rarely been explored in the literature. Herein, we synthesize a series of PBAE-based CANs by aza-Michael addition, using diacrylate monomers with and without β-hydroxyl groups, and a triamine crosslinker. By leveraging hydrogen bonding, the thermal and mechanical properties of these PBAE-based CANs are effectively tuned through the monomer composition. Owing to the numerous tertiary amines serving as internal catalysts, these CANs undergo catalyst-free network exchange through a dynamic aza-Michael reaction. Interestingly, increasing the amount of βhydroxyl groups accelerates overall stress relaxation from the synergistic effects of transesterification (associative type) at lower temperatures and dynamic aza-Michael reaction (dissociative type) at higher temperatures. Based on these features, we successfully demonstrate the reprocessing and healing at elevated temperatures under mild pressure, as well as shape memory and shape reconfiguration. Thus, controlling the β-hydroxyl group concentration in PBAE-based CANs is a useful strategy for enhancing both the mechanical strength and reprocessing rate.

Globally rising environmental concerns have increased the demand for recyclable polymers and efficient recycling practices. The lack of melt-processability of thermosets significantly limits their recycling because the simplest and most...

Among the various types of shape changing materials, liquid crystal elastomers (LCEs) have received significant attention as they can undergo programmed and reversible shape transformations. The molecular engineering of LCEs is the key to manipulating their phase transition, mechanical properties, and actuation performance. In this work, LCEs containing three different types of butyl groups (n-, iso-, and sec-butyl) in the side chain were synthesized, and the effect of isomeric amine chain extenders on the thermal, mechanical, and actuation properties of the resulting LCEs was investigated. Because of the considerably low reactivity of the sec-butyl group toward the diacrylate in the LC monomer, only a densely crosslinked LCE was synthesized. Most interestingly, the mechanical properties, actuation temperature, and blocking stress of the LCEs comprising isobutyl groups were higher than those of the LCEs comprising n-butyl groups. This difference was attributed to the presence of branches in the LCEs with isobutyl groups, which resulted in a tighter molecular packing and reduced the free volume. Our results suggest a facile and effective method for synthesizing LCEs with tailored mechanical and actuation properties by the choice of chain extenders, which may advance the development of soft actuators for a variety of applications in aerospace, medicine, and optics.

The network structures of liquid crystal elastomers (LCEs) are crucial to impart rubbery behavior to LCEs and enable reversible actuation. Most LCEs developed to date are covalently linked, implying that the cross-links are fixed at a particular position. Herein, we report a new class of LCEs integrating polyrotaxanes (PRs) as slidable cross-links (PR-LCEs). Interestingly, the incorporation of a low loading (0.3–2.0 wt %) of the PR cross-linkers to the LCE causes a significant impact on various properties of the resulting PR-LCEs due to the pulley effect. The optimum PR loading is determined to be 0.5 wt %, at which point the toughness and damping behavior are maximized. The robust mechanical properties of the PR-LCE offers a superior actuation performance to that of the pristine LCE along with an excellent quadruple shape-memory effect. Furthermore, the incorporation of PR is useful to enhance the efficiency of shape-memory-assisted self-healing when heating above the nematic–isotropic transition.