Reversible Curvature Reversal of Monolithic Liquid Crystal Elastomer Film and Its Smart Valve Application

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.

Shape programming of liquid crystal elastomers

Liquid crystal elastomers (LCEs) are shape-morphing materials that demonstrate reversible actuation when exposed to external stimuli, such as light or heat. The actuation's complexity depends heavily on the instilled liquid crystal alignment, programmed into the material using various shape-programming processes. As an unavoidable part of LCE synthesis, these also introduce geometrical and output restrictions that dictate the final applicability. Considering LCE's future implementation in real-life applications, it is reasonable to explore these limiting factors. This review offers a brief overview of current shape-programming methods in relation to the challenges of employing LCEs as soft, shape-memory components in future devices.

From Light-Powered Motors, to Micro-Grippers, to Crawling Caterpillars, Snails and Beyond-Light-Responsive Oriented Polymers in Action

"How would you build a robot, the size of a bacteria, powered by light, that would swim towards the light source, escape from it, or could be controlled by means of different light colors, intensities or polarizations?" This was the question that Professor Diederik Wiersma asked PW on a sunny spring day in 2012, when they first met at LENS-the European Laboratory of Nonlinear Spectroscopy-in Sesto Fiorentino, just outside Florence in northern Italy. It was not just a vague question, as Prof. Wiersma, then the LENS director and leader of one of its research groups, already had an idea (and an ERC grant) about how to actually make such micro-robots, using a class of light-responsive oriented polymers, liquid crystal elastomers (LCEs), combined with the most advanced fabrication technique-two-photon 3D laser photolithography. Indeed, over the next few years, the LCE technology, successfully married with the so-called direct laser writing at LENS, resulted in a 60 micrometer long walker developed in Prof. Wiersma's group (as, surprisingly, walking at that stage proved to be easier than swimming). After completing his post-doc at LENS, PW returned to his home Faculty of Physics at the University of Warsaw, and started experimenting with LCE, both in micrometer and millimeter scales, in his newly established Photonic Nanostructure Facility. This paper is a review of how the ideas of using light-powered soft actuators in micromechanics and micro-robotics have been evolving in Warsaw over the last decade and what the outcomes have been so far.

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

Fibrous soft actuators with high molecular anisotropy are of interest for shape morphing from 1D to 2D and 3D in response to external stimuli with high actuation efficiency. Nevertheless, few have fabricated fibrous actuators with controlled molecular orientations and stiffness. Here, we fabricate filaments from liquid crystal networks (LCNs) with segmental crosslinking density and gradient porosity from a mixture of di-acrylate mesogenic monomers and small-molecule nematic or smectic liquid crystals (LCs) filled in a capillary. During photopolymerization, phase separation between the small-molecule LCs and LCN occurs, making one side of the filament considerably denser than the other side. To direct its folding mode (bending or twisting), we control the alignment of LC molecules within the capillary, either along or perpendicular to the filament long axis. We show that the direction of UV exposure can determine the direction of phase separation, which in turn direct the deformation of the filament after removal of the small-molecule LCs. We find that the vertical alignment of LCs within the filament is essential to efficiently direct bending deformation. By photopatterning the filament with segmental crosslinking density, we can induce a reversible folding/unfolding into 2D and 3D geometries triggered by deswelling/swelling in an organic solvent. Moreover, by taking advantage of the large elastic modulus of LCNs and large contrast of the modulus before and after swelling, we show that the self-folded LCP filament could act as a strong gripper.

Light-Driven Linear Inchworm Motor Based on Liquid Crystal Elastomer Actuators Fabricated with Rubbing Overwriting

Linear displacement is used for positioning and scanning, e.g., in robotics at different scales or in scientific instrumentation. Most linear motors are either powered by rotary drives or are driven directly by pressure, electromagnetic forces or a shape change in a medium, such as piezoelectrics or shape-memory materials. Here, we present a centimeter-scale light-powered linear inchworm motor, driven by two liquid crystal elastomer (LCE) accordion-like actuators. The rubbing overwriting technique was used to fabricate the LCE actuators, made of elastomer film with patterned alignment. In the linear motor, a scanned green laser beam induces a sequence of travelling deformations in a pair of actuators that move a gripper, which couples to a shaft via friction moving it with an average speed in the order of millimeters per second. The prototype linear motor demonstrates how LCE light-driven actuators with a limited stroke can be used to drive more complex mechanisms, where large displacements can be achieved, defined only by the technical constrains (the shaft length in our case), and not by the limited strain of the material. Inchworm motors driven by LCE actuators may be scaled down to sub-millimeter size and can be used in applications where remote control and power supply with light, either delivered in free space beams or via fibers, is an advantage.