A Light-Powered Liquid Crystal Elastomer Spring Oscillator with Self-Shading Coatings

Fabrication and Photothermal Actuation Performances of Electrospun Carbon Nanotube/Liquid Crystal Elastomer Blend Yarn Actuators

Liquid crystal elastomers (LCEs) are a kind of polymer network that combines the entropic elasticity of polymer networks and the mesogenic unit by means of mild cross-linking. LCEs have been extensively investigated in various fields, including artificial muscles, actuators, and microrobots. However, LCEs are characterized by the poor mechanical properties of the light polymers themselves. In this study, we propose to prepare a carbon nanotube/liquid crystal elastomer (CNT/LCE) composite yarn by electrospinning technology and a two-step cross-linking strategy. The CNT/LCE composite yarn exhibits a reversible shrinkage ratio of nearly 70%, a tensile strength of 16.45 MPa, and a relatively sensitive response speed of ∼3 s, enabling a fast response by photothermal actuation. The research disclosed in this article may provide new insights for the development of artificial muscles and next-generation smart robots.

Liquid crystal elastomer self-oscillator with embedded light source

Light sources that switch periodically over time have a wide range of application value in life and engineering, and generally require additional controller to periodically switch circuits to achieve periodic lighting. In this paper, a self-oscillating spring oscillator based on optically responsive liquid crystal elastomer (LCE) fiber is constructed, which consists of a embedded light source and a LCE fiber. The spring oscillator can oscillate autonomously to achieve periodic switching of the light source. On the basis of the well-established dynamic LCE model, a nonlinear dynamic model is proposed and its dynamic behavior is studied. Numerical calculations demonstrate that the spring oscillator presents two motion regimes, namely the self-oscillation regime and the static regime. The self-oscillation of spring oscillator is maintained by the energy competition between light energy and damping dissipation. Furthermore, the critical conditions for triggering self-oscillation are also investigated in detail, as well as the key system parameters that affect its frequency and amplitude. Different from the existing abundant self-oscillating systems, this self-oscillating structure with simple structure and convenient fabrication does not require complex controller to obtain periodic lighting, and it is expected to provide more diversified design ideas for soft robots and sensors.

Self-sustained chaotic floating of a liquid crystal elastomer balloon under steady illumination

Self-sustained chaotic system has the capability to maintain its own motion through directly absorbing energy from the steady external environment, showing extensive application potential in energy harvesters, self-cleaning, biomimetic robots, encrypted communication and other fields. In this paper, a novel light-powered chaotic self-floating system is proposed by virtue of a nonlinear spring and a liquid crystal elastomer (LCE) balloon, which is capable of self-floating under steady illumination due to self-beating. The corresponding theoretical model is formulated by combining dynamic LCE model and Newtonian dynamics. Numerical calculations show that the periodic self-floating of LCE balloon can occur under steady illumination, which is attributed to the light-powered self-beating of LCE balloon with shading coating. Furthermore, the chaotic self-floating is presented to be developed from the periodic self-floating through period doubling bifurcation. In addition, the effects of system parameters on the self-floating behaviors of the system are also investigated. The detailed calculations demonstrate that the regime of self-floating LCE balloon depends on a combination of system parameters. The chaotic self-floating system of current study may inspire the design of other chaotic self-sustained motion based on stimuli-responsive materials, and have guiding significance for energy harvesters, self-cleaning, biomimetic robots, encrypted communication and other applications.

Thermally Driven Continuous Rolling of a Thick-Walled Cylindrical Rod

Self-sustained motion can take advantage of direct energy extraction from a steady external environment to maintain its own motion, and has potential applications in energy harvesting, robotic motion, and transportation. Recent experiments have found that a thermally responsive rod can perform self-sustained rolling on a flat hot plate with an angular velocity determined by the competition between the thermal driving moment and the friction moment. A rod with a hollow cross section tends to greatly reduce the frictional resistance, while promising improvements in thermal conversion efficiency. In this paper, through deriving the equilibrium equations for steady-state self-sustained rolling of the thick-walled cylindrical rod, estimating the temperature field on the rod cross-section, and solving the analytical solution of the thermally induced driving moment, the dynamic behavior of the thermally driven self-sustained rolling of the thick-walled cylindrical rod is theoretically investigated. In addition, we investigate in detail the effects of radius ratio, heat transfer coefficient, heat flux, contact angle, thermal expansion coefficient, and sliding friction coefficient on the angular velocity of the self-sustained rolling of the thick-walled cylindrical rod to obtain the optimal ratio of internal and external radius. The results are instructive for the application of thick-walled cylindrical rods in the fields of waste heat harvesters and soft robotics.

Dynamical Behaviors of a Translating Liquid Crystal Elastomer Fiber in a Linear Temperature Field

Liquid crystal elastomer (LCE) fiber with a fixed end in an inhomogeneous temperature field is capable of self-oscillating because of coupling between heat transfer and deformation, and the dynamics of a translating LCE fiber in an inhomogeneous temperature field are worth investigating to widen its applications. In this paper, we propose a theoretic constitutive model and the asymptotic relationship of a LCE fiber translating in a linear temperature field and investigate the dynamical behaviors of a corresponding fiber-mass system. In the three cases of the frame at rest, uniform, and accelerating translation, the fiber-mass system can still self-oscillate, which is determined by the combination of the heat-transfer characteristic time, the temperature gradient, and the thermal expansion coefficient. The self-oscillation is maintained by the energy input from the ambient linear temperature field to compensate for damping dissipation. Meanwhile, the amplitude and frequency of the self-oscillation are not affected by the translating frame for the three cases. Compared with the cases of the frame at rest, the translating frame can change the equilibrium position of the self-oscillation. The results are expected to provide some useful recommendations for the design and motion control in the fields of micro-robots, energy harvesters, and clinical surgical scenarios.

Photothermal Thin Films with Highly Efficient NIR Conversion for Miniaturized Liquid-Crystal Elastomer Actuators

This work presents the development of highly efficient photothermal thin films (PTFs) and the demonstration of their application on miniaturized polymer-based soft actuators. The proposed PTF, which comprises acrylic-based black paint and EGaIn liquid metal (LM) microdroplets, serves as an excellent absorber for efficiently converting near-infrared (NIR) irradiation into heat for actuating liquid-crystal elastomer (LCE) actuators. The introduction of LM microdroplets into the PTFs effectively increases the overall thermal efficiency of PTFs. Miniaturized soft crawlers monolithically integrated with the NIR-driven LCE actuators are also implemented for demonstrating the application of the proposed PTF. The crawler’s locomotion, which is inspired by the rectilinear movement of snakes, is generated with the proposed PTF for inducing the LC-to-isotropic phase transition of the LCEs. The experimental results show that introducing LM microdroplets into the PTF can effectively reduce the thermal time constants of LCE actuators by 70%. Under periodic on/off NIR illumination cycles, the locomotion of crawlers with different dimensions is also demonstrated. The measurement results indicate that the proposed PTF is not only essential for enabling photothermal LCE actuation but also quite efficient and durable for repeated operation.

Self-Jumping of a Liquid Crystal Elastomer Balloon under Steady Illumination

Self-oscillation capable of maintaining periodic motion upon constant stimulus has potential applications in the fields of autonomous robotics, energy-generation devices, mechano-logistic devices, sensors, and so on. Inspired by the active jumping of kangaroos and frogs in nature, we proposed a self-jumping liquid crystal elastomer (LCE) balloon under steady illumination. Based on the balloon contact model and dynamic LCE model, a nonlinear dynamic model of a self-jumping LCE balloon under steady illumination was formulated and numerically calculated by the Runge–Kutta method. The results indicated that there exist two typical motion regimes for LCE balloon under steady illumination: the static regime and the self-jumping regime. The self-jumping of LCE balloon originates from its expansion during contact with a rigid surface, and the self-jumping can be maintained by absorbing light energy to compensate for the damping dissipation. In addition, the critical conditions for triggering self-jumping and the effects of several key system parameters on its frequency and amplitude were investigated in detail. The self-jumping LCE hollow balloon with larger internal space has greater potential to carry goods or equipment, and may open a new insight into the development of mobile robotics, soft robotics, sensors, controlled drug delivery, and other miniature device applications.