Search Results (105)

Liquid crystal elastomers (LCEs) have shown great potential in the field of soft robotics due to their unique actuation capabilities. Despite the growing number of experimental studies in the soft robotics field, theoretical research remains limited. In this paper, a dynamic model of a bionic arm using an LCE fiber as artificial muscle is established, which exhibits periodic oscillation controlled by periodic illumination. Based on the assumption of linear damping and angular momentum theorem, the dynamics equation of the model oscillation is derived. Then, based on the assumption of linear elasticity model, the periodic spring force of the fiber is given. Subsequently, the evolution equations for the cis number fraction within the fiber are developed, and consequently, the analytical solution for the light-excited strain is derived. Following that, the dynamics equation is numerically solved, and the mechanism of the controllable oscillation is elucidated. Numerical calculations show that the stable oscillation period of the bionic arm depends on the illumination period. When the illumination period aligns with the natural period of the bionic arm, the resonance is formed and the amplitude is the largest. Additionally, the effects of various parameters on forced oscillation are analyzed. The results of numerical studies on the bionic arm can provide theoretical support for the design of micro-machines, bionic devices, soft robots, biomedical devices, and energy harvesters. Full article

Electroactive polymers (EAPs) represent a versatile class of smart materials capable of converting electrical stimuli into mechanical motion and vice versa, positioning them as key components in the next generation of actuators and sensors. This review summarizes recent developments in both electronic and ionic EAPs, highlighting their activation mechanisms, material architectures, and multifunctional capabilities. Representative systems include dielectric elastomers, ferroelectric and conducting polymers, liquid crystal elastomers, and ionic gels. Advances in fabrication methods, such as additive manufacturing, nanocomposite engineering, and patternable electrode deposition, are discussed with emphasis on miniaturization, stretchability, and integration into soft systems. Applications span biomedical devices, wearable electronics, soft robotics, and environmental monitoring, with growing interest in platforms that combine actuation and sensing within a single structure. Finally, the review addresses critical challenges such as long-term material stability and scalability, and outlines future directions toward self-powered, AI-integrated, and sustainable EAP technologies. Full article

The realization of broad-wavelength tunability of the structural color in Double layered Cholesteric Liquid Crystal Elastomers (DCLCEs), along with good flexibility and processability, presents a significant challenge. This research introduces a facile and effective fabrication technique, Solvent Evaporation-Induced Self-Assembly (SEISA), for the production of DCLCEs exhibiting broad wavelength tunability, superior flexibility, and robust mechanical characteristics. Focusing on initial color tuning, bubble defect minimization, UV photopolymerization, and coating procedures, this research systematically optimizes the fabrication process through experimental investigation of factors like chiral dopant amount, temperature, UV exposure duration, coating thickness, and speed. The method enabled the successful fabrication of DCLCEs with uniform and controllable coloration, demonstrating the effectiveness of this controlled synthesis approach in significantly enhancing structural color features. Upon stretching to 2.8 times its original length, the center wavelength shifted from 613 nm to 404 nm, yielding a tunable bandwidth of up to 209 nm across the visible spectrum. Full article

Metallic thin-walled porous tubes have been widely applied in energy absorption fields due to their unique mechanical properties. Inspired by foam-filled structures, liquid crystal elastomers as a new category of metamaterials were filled in metallic thin-walled porous tubes to obtain a novel composite energy-absorbing structure that can improve energy-absorbing capabilities. By means of experiments and numerical simulations, this paper investigated deformation modes and the energy-absorbing performance of metallic thin-walled porous tubes filled with liquid crystal elastomers under dynamic crush. Moreover, the effects of geometric parameters on deformation modes and the energy-absorbing performance of the metallic thin-walled porous tubes filled with liquid crystal elastomers were analyzed. The results show that liquid crystal elastomers can enhance energy-absorbing capabilities under dynamic crush and geometric parameters can affect deformation modes, further affecting the energy-absorbing performance of metallic thin-walled porous tubes filled with liquid crystal elastomers. Full article

Plant tendrils exhibit intriguing tropism motions like bending, twisting, and coiling. Herein, we report the application of a liquid crystal elastomer (LCE) to make a light-sensitive and biomimetic coil to replicate behaviors of plant tendrils. The LCE coil consists of diacrylate azobenzene, diacrylate mesogens, and thiol-based spacers. These components are first mixed to form a highly viscous prepolymer solution through a thiol-acrylate Michael addition reaction. Subsequently, an extrusion–rolling process is developed to draw the viscous solution into a coil, which is mechanically stretched in a single direction to align mesogens in the LCE. Finally, the coil is photopolymerized under UV light to form an LCE coil with a diameter of 375 µm. The LCE coil possesses good rigidity and flexibility and shows movement upon light exposure. For example, the LCE coil shows a reversible bending up to 120° to 365 nm UV and 30% contraction to 455 nm visible light, respectively, due to trans-cis photoisomerization of azobenzene derivatives. When the coil is irradiated with UV light with an intensity up to 10 mW cm⁻², it can twist and coil up. It can also wrap around the UV light tube in 6 s, similar to a plant tendril. This type of light-responsive coil has great potential in making biomimetic plants or soft robotics. Full article

While liquid crystal elastomers (LCEs) show promise for diverse soft actuators due to their strong stimulus responsiveness, limited investigation into their light perception and processing restricts their wider use in intelligent systems. This study employs a hollow double-layer structure to design light-controlled logic soft switches based on LCEs. The design realizes digital logic circuits including AND gates, OR gates, and NOT gates, as well as an optical switch array capable of converting light signals into visualized digital signals. These light-controlled soft switches exhibit strong photothermal responsiveness (~12 s), high programmability, and excellent cyclic stability (>500 times). This research provides a new perspective on light-controlled logic soft switches and their applications in logic circuits. Full article

The chemical response of liquid crystal elastomers (LCEs) offers substantial potential for applications in propulsion systems, micromechanical systems, and active smart surfaces. However, the shape-changing behaviors of LCEs in response to organic (isotropic) solvents remain scarcely explored, with most research focusing on liquid crystal (anisotropic) solvents. Herein, we prepared a series of aligned LCEs with varying crosslink densities using a surface alignment technique combined with an aza-Michael addition reaction, aiming to investigate their swelling behaviors in different isotropic solvents. We found that the rates of shape and volume variation modes, the elastic modulus of the LCEs, and the polarity of the solvent all significantly influence the swelling behavior. Specifically, when LCEs swell in acetone, dimethylformamide (DMF), and ethyl acetate, contraction occurs along the alignment direction. Conversely, extension along the alignment direction is observed when LCEs swell in toluene, anisole, and acrylic acid. Meanwhile, extension in the perpendicular direction is noted when LCEs swell in nearly all solvents. These shape changes can be attributed to the phase transitions of the LCEs. This research not only provides valuable insights into the swelling mechanisms of LCEs but also holds great promise for the development of solvent sensors and gas sensing applications. Full article

The development and electrochemical characteristics of ionic liquid crystal elastomers (iLCEs) are described for use as electrolyte components in lithium-ion batteries. The unique combination of elastic and liquid crystal properties in iLCEs grants them robust mechanical attributes and structural ordering. Specifically, the macroscopic alignment of phase-segregated, ordered nanostructures in iLCEs serves as an ion pathway, which can be solidified through photopolymerization to create ion-conductive solid-state polymer lithium batteries (SSPLBs) with high ionic conductivity (1.76 × 10⁻³ S cm⁻¹ at 30 °C), and a high (0.61) transference number. Additionally, the rubbery state ensures good interfacial contact with electrodes that inhibits lithium dendrite formation. Furthermore, in contrast to liquid electrolytes, the iLCE shrinks upon heating, thus preventing any overheating-related explosions. The Li/LiFePO₄ (LFP) cells fabricated using iLCE-based solid electrolytes show excellent cycling stability with a discharge capacity of ~124 mAh g⁻¹ and a coulombic efficiency close to 100%. These results are promising for the practical application of iLCE-based SSPLBs. Full article

Soft robots, constructed from deformable materials, offer significant advantages over rigid robots by mimicking biological tissues and providing enhanced adaptability, safety, and functionality across various applications. Central to these robots are electroactive polymer (EAP) actuators, which allow large deformations in response to external stimuli. This review examines various EAP actuators, including dielectric elastomers, liquid crystal elastomers (LCEs), and ionic polymers, focusing on their potential as artificial muscles. EAPs, particularly ionic and electronic varieties, are noted for their high actuation strain, flexibility, lightweight nature, and energy efficiency, making them ideal for applications in mechatronics, robotics, and biomedical engineering. This review also highlights piezoelectric polymers like polyvinylidene fluoride (PVDF), known for their flexibility, biocompatibility, and ease of fabrication, contributing to tactile and pressure sensing in robotic systems. Additionally, conducting polymers, with their fast actuation speeds and high strain capabilities, are explored, alongside magnetic polymer composites (MPCs) with applications in biomedicine and electronics. The integration of machine learning (ML) and the Internet of Things (IoT) is transforming soft robotics, enhancing actuation, control, and design. Finally, the paper discusses future directions in soft robotics, focusing on self-healing composites, bio-inspired designs, sustainability, and the continued integration of IoT and ML for intelligent, adaptive, and responsive robotic systems. Full article

Conventional machines often face limitations due to complex controllers and bulky power supplies, which can hinder their reliability and operability. In contrast, self-excited movements can harness energy from a stable environment for self-regulation. In this study, we present a novel model of a self-rowing boat inspired by paddle boats. This boat is powered by a liquid crystal elastomer (LCE) turntable that acts as a motor and operates under consistent illumination. We investigated the dynamic behavior of the self-rowing boat under uniform illumination by integrating the photothermal reaction theory of LCEs with a nonlinear dynamic framework. The primary equations were solved using the fourth-order Runge–Kutta method. Our findings reveal that the model exhibits two modes of motion under steady illumination: a static pattern and a self-rowing pattern. The transition between these modes is influenced by the interaction of the driving and friction torques generated by photothermal energy. This study quantitatively analyzes the fundamental conditions necessary for initiating a self-rowing motion and examines how various dimensionless parameters affect the speed of the self-rowing system. The proposed system offers several unique advantages, including a simple structure, easy control, and independence from electronic components. Furthermore, it has the potential for miniaturization and integration, enhancing its applicability in miniature machines and systems. Full article

The reliance of feedback mechanisms in conventional light-fueled self-oscillating systems on spatially distributed light and intricately designed structures impedes their application and development in micro-robots, miniature actuators, and other small-scale devices. This paper presents a straightforward rheostat feedback mechanism to create an electrically driven liquid crystal elastomer (LCE) self-oscillator which comprises an LCE fiber, a rheostat, a spring, and a mass. Based on the electrothermally responsive LCE model, we first derive the governing equation for the system’s dynamics and subsequently formulate the asymptotic equation. Numerical calculations reveal two motion phases, i.e., static and self-oscillating, and elucidate the mechanism behind self-oscillation. By employing the multi-scale method, we identify the Hopf bifurcation and establish the analytical solutions for amplitude and frequency. The influence of various system parameters on the amplitude and frequency of self-oscillation was analyzed, with numerical solutions being validated against analytical results to ensure consistency. The proposed rheostat feedback mechanism can be extended to cases with rheostats that have more general resistance properties and offers advantages such as simple design, adjustable dimensions, and rapid operation. The findings are expected to inspire broader design concepts for applications in soft robotics, sensors, and adaptive structures. Full article

Liquid crystal elastomers (LCEs) are innovative materials best known for their reversible shape and optical property changes in response to external stimuli such as heat, light, and mechanical forces. These unique features position them as promising candidates for applications in emerging technologies. The determination of the mechanical properties of these materials is important for the study of the interaction between orientational and mechanical deformations of LCEs. Importantly, thoroughly characterizing the mechanical and elastic properties of LCEs is essential for their efficient design and integration into various devices. In this study, a full elastic characterization of promising acrylate-based LCE materials that are auxetic above a material-dependent strain threshold (~0.4 for the material studied here) was carried out. Highly aligned macroscopic samples were fabricated, allowing us to determine, for the first time, the five elasticity coefficients that enter into the elastic-free energy density of acrylate-based LCE materials, as well as the Young’s moduli and Poisson ratios. Our approach involves connecting measured strains with elasticity coefficients and using data obtained from three tensile experiments. Specifically, the measured Young’s moduli are on the order of MPa, with an anisotropy ratio (E‖/E⊥) of ~4.5. Moreover, the longitudinal Poisson ratios are both close to 0.5, confirming a uniaxial elastic response at low strains in these LCE samples. These findings align with theoretical predictions, indicating a good correspondence between experimental results and established theories. Full article

Liquid crystal elastomers (LCE) are a promising material to achieve reversible actuation while being able to perform work, showing great potential as artificial muscles in soft robotics and medical technology. Here, a wet spinning process to prepare liquid crystal elastomer fibers (LCEF) with reversible actuation capability is presented. Furthermore, we demonstrate the ability to process side-chain liquid crystal (LC) 4-Methoxyphenyl 4-(3-butenyloxy)benzoate (MBB) into a fiber, enlarging the material variance available in this field. The wet spinning process is presented and discussed in terms of spinning parameters and their influence on fiber properties, especially LC orientation. Moderate draw ratios of up to 2.3 enable highly oriented mesogens (f = 0.64), enabling the contractile behavior. The generated MBB-based LCEF show low activation temperature (54.52 °C), temperature-dependent mechanical properties, reversible contraction behavior while lifting up to 140 times their own weight and are able to perform work of up to 3.857 J kg⁻¹. Actuation properties are compared with human skeletal muscle, and possible strategies of further enhancing the LCEF performance are discussed. The generated data show promising features of the LCEF for use as artificial muscle fibers in medical applications, e.g., prosthetics and artificial cardiac tissue. Full article

Self-excited systems rely on stable external stimuli to initiate and sustain oscillations via internal processes. However, these oscillations can compromise system stability and increase friction, limiting their practical applications. To overcome this issue, we propose the light-fueled stable self-rolling of a liquid crystal elastomer (LCE)-based wheel. A photothermal response model based on an LCE was used to analyze the temperature distribution within the LCE rods. The driving torque for self-rolling is generated by the contraction resulting from the LCE’s photothermal response, which displaces the wheel’s center of mass. We then derived the equilibrium equations and identified the critical conditions for achieving stable self-rolling motion. Through the interaction between the temperature field and driving torque, the wheel achieves continuous and stable self-rolling by absorbing thermal energy to counteract damping dissipation. Numerical simulations revealed that the stable self-rolling velocity is influenced by several key parameters, including heat flux, the contraction coefficient, gravitational acceleration, the initial damping torque, and the rolling damping coefficient. The proposed LCE-based wheel enhances system stability and significantly reduces frictional losses. These characteristics make it a promising candidate for applications in autonomous drive systems, micro-transportation devices, and photothermal energy conversion technologies. Full article

This work aims to determine the mechanism of the photomechanical response of poly(Methyl methacrylate) polymer doped with the photo-isomerizable dye Disperse Red 1 using the non-isomerizable dye Disperse Orange 11 as a control to isolate photoisomerization. Samples are free-standing thin films with thickness that is small compared with the optical skin depth to assure uniform illumination and photomechanical response throughout their volume, which differentiates these studies from most others. Polarization-dependent measurements of the photomechanical stress response are used to deconvolute the contributions of angular hole burning, molecular reorientation and photothermal heating. While photo-isomerization of dopant molecules is commonly observed in dye-doped polymers, the shape changes of a molecule might not couple strongly to the host polymer through steric mechanical interactions, thus not contributing substantially to a macroscopic shape change. To gain insights into the effectiveness of such mechanical coupling, we directly probe the dopant molecules using dichroism measurements simultaneously while measuring the photomechanical response and find mechanical coupling to be small enough to make photothermal heating—mediated by the transfer of optical energy as heat to the polymer—the dominant mechanism. We also predict the fraction of light energy converted to mechanical energy using a model whose parameters are thermodynamic material properties that are measured with independent experiments. We find that in the thin-film geometry, these dye-doped glassy polymers are as efficient as any other material but their large Young’s modulus relative to other organic materials, such as liquid crystal elastomers, makes them suitable in applications that require mechanically strong materials. The mechanical properties and the photomechanical response of thin films are observed to be significantly different than in fibers, suggesting that the geometry of the material and surface effects might play an important role. Full article