Self-Folding Liquid Crystal Network Filaments Patterned with Vertically Aligned Mesogens

Fast and Slow-Twitch Actuation via Twisted Liquid Crystal Elastomer Fibers

The performance of robotic systems can benefit from low-density material actuators that emulate muscle typology (e.g., fast and slow twitch) of natural systems. Recent reports detail the thermomechanical, chemical, electrical, and pneumatic response of twisted and coiled fibers. The geometrical constraints imparted on typically commodity materials realize distinguished stimuli-induced actuation including low density, high force, and moderate stroke. Here, actuators are prepared by twisting fibers composed of liquid crystal elastomers (LCEs). The actuators combine the inherent stimuli-response of LCEs with the geometrical constraints of twisted fiber actuators to dramatically increase the deformation rate, specific work, and achievable force output. In some geometries, the thermomechanical response of the LCE exhibits a pseudo-first-order transition.

Sidewinder-Inspired Self-Adjusting, Lateral-Rolling Soft Robots for Autonomous Terrain Exploration

Helical structures of liquid crystal elastomers (LCEs) hold promise in soft robotics for self-regulated rolling motions. The understanding of their motion paths and potentials for terrain exploration remains limited. This study introduces a self-adjusting, lateral-rolling soft robot inspired by sidewinder snakes. The spring-like LCE helical filaments (HFs) autonomously respond to thermal cues, demonstrating dynamic and sustainable locomotion with adaptive rolling along non-linear paths. By fine-tuning the diameter, pitch, and modulus of the LCE HFs, and the environmental temperature, the movements of the LCE HFs, allowing for exploration of diverse terrains over a 600 cm2 area within a few minutes, can be programmed. LCE HFs are showcased to navigate through over nine obstacles, including maze escaping, terrain exploration, target hunting, and successfully surmounting staircases through adaptable rolling.

Exploiting Molecular Orders at the Interface of Microdroplets for Intelligent Materials

ConspectusThe intrinsic molecular order of liquid crystals (LCs) and liquid crystalline elastomers (LCEs) is the origin of their stimuli-responsive properties. The programmable responsiveness and functionality, such as shape morphing and color change under external stimuli, are the key features that attract interest in designing LC- and LCE-based intelligent material platforms. Methods such as mechanical stretching and shearing, surface alignment, and field-assisted alignment have been exploited to program the order of LC molecules for the desired responsiveness. However, the huge size mismatch between the nanometer-sized LC mesogens and the targeted macroscopic objects calls for questions about how to delicately control molecular order for desired performance. Microparticles that can be synthesized with intrinsic molecular order precisely controlled to micrometer size can be used as building blocks for bulk materials, thus offering opportunities to bridge the gap and transcend molecular orders across scales. By taking advantage of the interfacial anchoring effects, we can control and engineer the molecular orders inside the microdroplets, allowing for the realization of various responsive behaviors. Furthermore, designer LC microparticles with multiple responsiveness can be assembled and confined within a matrix, opening a new pathway to engineering LC-enabled intelligent materials.In this Account, we present our recent work on exploiting the molecular order inside microdroplets for the construction of intelligent materials. We briefly introduce the typical chemicals used in the synthesis and the methods developed to control LC molecular alignment within a microdroplets. We then present examples of microparticles synthesized from microdroplets that can transform into complex morphologies upon cooling from the isotropic to nematic phase or due to phase separation within the droplets coupled with the segregation of LC oligomers (LCOs) with polydisperse chain lengths. Furthermore, we show the synthesis of elliptical LCE microparticles and exploit their thermal and magnetic responsiveness to program shape-morphing behaviors and microarrays with switchable optical polarization. By mixing magnetic nanoparticles in cholesteric liquid crystals (CLCs) and silicone oils, we created Janus microparticles capable of color switching for camouflage and information encryption. Moreover, we can engineer complex molecular orders in LCE microparticles by mixing different surfactants, yielding microparticles of diverse anisotropic, temperature-responsive shapes after photopolymerization and extraction of the template LC molecules with different solvents. We conclude the Account with an outlook on the design of intelligent material systems via the design of unprecedented molecular ordering within the microparticles and their coupling with bulk materials.

High-Performance Electrochemical Actuator under an Ultralow Driving Voltage with a Mixed Electronic-Ionic Conductive Metal-Organic Framework

Although versatile deformation, high flexibility, and environmental friendliness of electrochemical actuators (EAs) have made them promising in bioinspired soft robots and biomedical devices, the relatively high driving voltages unfortunately impose great restrictions on their applications in low-energy and human-friendly electronics. Here, we find that the uses of a mixed electronic-ionic conductive metal-organic framework (c-MOF), i.e., Ni3(hexaiminotriphenylene)2 (Ni3(HITP)2), largely lower the driving voltage of EAs. The as-fabricated EA can work under a driving voltage as low as 0.1 V, representing the lowest value among those for the c-MOF-based EAs reported so far. The Ni3(HITP)2-based EA shows an excellent actuation performance such as a high bending strain difference of 0.48% (±0.5 V, 0.1 Hz) and long-term durability of >99% after 15,000 cycles due to the improved conductivity up to 1000 S·cm-1 and double-layer capacitance as high as 176.3 F·g-1 stemming from the mixed electronic-ionic conduction of Ni3(HITP)2.

Autonomous, untethered gait-like synchronization of lobed loops made from liquid crystal elastomer fibers via spontaneous snap-through

The transition from one equilibrium state to another via rapid snap-through can store elastic energy and release it as kinetic energy for rapid motion as seen in Venus flytrap and hummingbird to catch insects mid-flight. They are explored in soft robotics for repeated and autonomous motions. In this study, we synthesize curved liquid crystal elastomer (LCE) fibers as the building blocks that can undergo buckling instability upon heated on a hot surface, leading to autonomous snap-through and rolling behaviors. When they are connected into lobed loops, where each fiber is geometrically constrained by the neighboring ones, they demonstrate autonomous, self-regulated, and repeated synchronization with a frequency of ~1.8 Hz. By adding a rigid bead on the fiber, we can fine-tune the actuation direction and speed (up to ~2.4 mm/s). Last, we demonstrate various gait-like locomotion patterns using the loops as the robot's legs.