Liquid crystal elastomers (LCEs) offer promising prospect in applications such as soft robot actuators due to the fact that they can be chemically doped to have photo-responsive deformation ...characteristics. With the purpose of accurate control of LCE actuators in soft robot applications, the establishment of a model which quantitatively describes the deformation characteristics of LCE becomes essential. However, current models for LCE are very preliminary, which restricts the implementation of LCE actuators. This paper develops a model to describe the deformation of LCE actuators. First, the deformation process is discussed, which is in nature the macroscopic shape change corresponding to the phase change of LCE. Then, the relationship between the deformation and the temperature of LCE is established according to thermodynamic analysis on the free energy, and the phase transition process. Unknown parameters are determined through parameter identification with experimental data based on the non-linear least-squares method. This model has the advantage that it quantitatively describes the deformation characteristics of LCE without the aid of numerical simulation, and it reflects the physical nature of the deformation of LCE. This model lays a basis for the accurate control of the LCE actuators, which leads to future photo-responsive soft robot applications.
Anisotropic Mechanochromism
In article number 2310658, Suk‐kyun Ahn and co‐workers create cholesteric liquid crystal elastomers (CLCEs) with slanted helices via direct ink writing. Notably, the ...anisotropic mechanochromic response of the printed CLCE to being stretched relative to the printing direction is observed. The anisotropic mechanochromism enables the creation of a unique strain sensor displaying intricate and programmable color patterns upon stretching.
Digital Light Processing (DLP) 3D printing enables the creation of hierarchical complex structures with specific micro‐ and macroscopic architectures that are impossible to achieve through ...traditional manufacturing methods. Here, this hierarchy is extended to the mesoscopic length scale for optimized devices that dissipate mechanical energy. A photocurable, thus DLP‐printable main‐chain liquid crystal elastomer (LCE) resin is reported and used to print a variety of complex, high‐resolution energy‐dissipative devices. Using compressive mechanical testing, the stress–strain responses of 3D‐printed LCE lattice structures are shown to have 12 times greater rate‐dependence and up to 27 times greater strain–energy dissipation compared to those printed from a commercially available photocurable elastomer resin. The reported behaviors of these structures provide further insight into the much‐overlooked energy‐dissipation properties of LCEs and can inspire the development of high‐energy‐absorbing device applications.
Bespoke liquid crystal elastomer (LCE) lattice structures are 3D printed using Digital Light Processing from a custom thiol‐acrylate photocurable resin. The mechanical dissipation of these structures is explored and compared to a commercially available elastomer resin, TangoBlack. The LCE structures have greater reported rate‐dependence and dissipation properties. This can lead to the advent of better dissipative devices.
Three‐dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual ...thiol‐ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo‐responsive structures that sequentially and reversibly undergo multiple shape changes.
Novel inks for printable liquid crystal elastomers (LCEs) are reported herein. The 3D‐printed LCE structures undergo controlled and reversible shape change upon heating. By controlling the reaction parameters (e.g., reaction type, mesogen concentration, or crosslinking density), a wide range of LCEs are synthesized and characterized for their use as soft actuators.
Strain‐induced liquid crystallinity dramatically improves the toughness of elastomeric polymer networks. In their Communication on page 13744 ff., T. J. White et al. describe the mechanotropic phase ...transition of thiol‐ene photopolymers from a disorganized, isotropic state, to an organized, liquid crystalline state. Under stress, the liquid crystals reorient with the applied stress tensors resulting in significant strain hardening while maintaining rapid elastic recovery.
Liquid crystal elastomers (LCEs) are renowned for their large, reversible, and anisotropic shape change in response to various external stimuli due to their lightly cross‐linked polymer networks with ...an oriented mesogen direction, thus showing great potential for applications in robotics, bio‐medics, electronics, optics, and energy. To fully take advantage of the anisotropic stimuli‐responsive behaviors of LCEs, it is preferable to achieve a locally controlled mesogen alignment into monodomain orientations. In recent years, the application of 4D printing to LCEs opens new doors for simultaneously programming the mesogen alignment and the 3D geometry, offering more opportunities and higher feasibility for the fabrication of 4D‐printed LCE objects with desirable stimuli‐responsive properties. Here, the state‐of‐the‐art advances in 4D printing of LCEs are reviewed, with emphasis on both the mechanisms and potential applications. First, the fundamental properties of LCEs and the working principles of the representative 4D printing techniques are briefly introduced. Then, the fabrication of LCEs by 4D printing techniques and the advantages over conventional manufacturing methods are demonstrated. Finally, perspectives on the current challenges and potential development trends toward the 4D printing of LCEs are discussed, which may shed light on future research directions in this new field.
Liquid crystal elastomers (LCEs) exhibit attractive stimuli‐responsive properties, showing great application potential in soft robotics, biomedicine, optics, etc. The advent of 4D printing opens a new door for the design and fabrication of LCEs with programmable stimuli‐responsive properties and 3D geometries. The state‐of‐the‐art advances in 4D printing of LCEs are reviewed, with emphasis on both mechanisms and potential applications.
Nematic liquid crystal elastomers (LCEs) are advanced materials known for their shape-changing capability in response to external stimuli such as heat, light, solvents and electromagnetic fields. ...This makes them excellent candidates for applications like soft robotics and energy harvesting. While studies on their physical behavior have shed light on the complex nonlinear mechanics of LCEs, investigations through all-atom molecular dynamics (MD) simulations remain an underutilized avenue compared to experimental and theoretical analyses. This limited use is primarily due to the lack of well-established frameworks for conducting high-fidelity atomistic simulations of LCEs. To bridge this gap, we introduce an all-atom MD simulation framework based on the Polymer Consistent Force-Field (PCFF), which models the polymerization and crosslinking processes for a category of acrylate LCEs and captures their synthesis history- and composition-dependent properties. Our computational framework empowers us to simulate the spontaneous deformations and shape memory behavior upon temperature changes and enables us to observe the auxetic effect under elastic strains by generating models that closely replicate experimental findings. Moreover, this study not only validates the numerical models but opens up new avenues to explore the intricate behaviors of LCEs through their molecular structures and facilitate computational design advancements.
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•We develop all-atom molecular dynamics simulations for nematic LCE modeling.•The simulations capture synthesis history- and composition-dependent properties of LCEs.•The LCE models account for spontaneous deformations and shape memory effect upon temperature changes.•Auxetic behavior and the emergence of biaxial order are observed for a category of acrylate LCEs.•These LCE simulations enable further mechanistic understandings of nematic elastomers at molecular levels.
Direct ink writing of liquid crystal elastomers (LCEs) offers a new opportunity to program geometries for a wide variety of shape transformation modes toward applications such as soft robotics. So ...far, most 3D‐printed LCEs are thermally actuated. Herein, a 3D‐printable photoresponsive gold nanorod (AuNR)/LCE composite ink is developed, allowing for photothermal actuation of the 3D‐printed structures with AuNR as low as 0.1 wt.%. It is shown that the printed filament has a superior photothermal response with 27% actuation strain upon irradiation to near‐infrared (NIR) light (808 nm) at 1.4 W cm−2 (corresponding to 160 °C) under optimal printing conditions. The 3D‐printed composite structures can be globally or locally actuated into different shapes by controlling the area exposed to the NIR laser. Taking advantage of the customized structures enabled by 3D printing and the ability to control locally exposed light, a light‐responsive soft robot is demonstrated that can climb on a ratchet surface with a maximum speed of 0.284 mm s−1 (on a flat surface) and 0.216 mm s−1 (on a 30° titled surface), respectively, corresponding to 0.428 and 0.324 body length per min, respectively, with a large body mass (0.23 g) and thickness (1 mm).
3D‐printable photoresponsive gold nanorod/liquid crystal elastomer composite ink is formulated. Taking advantage of both the customizable printed structures from the 3D printing and the remoted, localized actuation from the NIR light, multiple shapes can be achieved, which allows more possible applications for artificial muscles, soft robotics, and other dynamic functional structures.
Stimulus responsive elastomers are advanced engineered materials that perform desired functionalities when triggered by external stimuli. Liquid crystal elastomers (LCEs) are one important example ...that exhibit reversible actuation when cycled above and below their nematic-to-isotropic transition temperature. Here, we propose a micromechanical-based model that is centered on the evolution of the chain distribution tensor of the LCE network. Our model, framed within the statistical model of the chain network, enables a mesoscale description of their mechanical response under an external thermal stimulus. We compare the model to prior experimental observations of the bending response of 3D printed LCE elements with controlled director alignment.
•A new light-fueled oscillatory self-snapping spherical shell is originally developed.•Two motion regimes of the static regime and the self-snapping regime are discovered.•The critical conditions of ...bistable state and light-driven contractions to trigger self-snapping are calculated.•Results are capable of aiding the design and control of the self-snapping LCE spherical shell.
Self-oscillation can absorb energy from constant external environment to maintain its own continuous motion, and has potential application in the fields of soft robotics, motors, military industry and so on. Inspired by the intermittent predation of Venus fly-trap, we creatively develop a pulsating self-snapping system in this paper, which is composed of liquid crystal elastomer (LCE) bilayer spherical shell under steady illumination. Based on shallow shell theory and dynamic LCE model, a nonlinear dynamic model of self-snapping shell is formulated. Through quasi-static analysis, the self-snapping of LCE bilayer shell under steady illumination is investigated by utilizing the modified iteration method. The LCE bilayer shell under steady illumination can develop into two motion regimes, namely the static regime and the self-snapping regime. The snapping-through of bilayer shell results from the light-driven bending moments tending to flatten the shell, and the self-snapping can be maintained by transforming between snap-through in illumination zone and snap-back in dark zone. In addition, the critical conditions for triggering self-snapping, and its energy release ratio are investigated in detail. Different from the existing abundant self-oscillating systems, this self-snapping system has advantages of large displacement, rapid energy release and high energy release ratio, and may pave a new way for the development of jumping robotics, actuated devices, military industry and so on.
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