Liquid crystal elastomers (LCEs) are of interest for applications such as soft robotics and shape‐morphing devices. Among the different actuation mechanisms, light offers advantages such as spatial ...and local control of actuation via the photothermal effect. However, the unwanted aggregation of the light‐absorbing nanoparticles in the LCE matrix will limit the photothermal response speed, actuation performance, and repeatability. Herein, a near‐infrared‐responsive LCE composite consisting of up to 0.20 wt% poly(ethylene glycol)‐modified gold nanorods (AuNRs) without apparent aggregation is demonstrated. The high Young's modulus, 20.3 MPa, and excellent photothermal performance render repeated and fast actuation of the films (actuation within 5 s and recovery in 2 s) when exposed to 800 nm light at an average output power of ≈1.0 W cm−2, while maintaining a large actuation strain (56%). Further, it is shown that the same sheet of AuNR/LCE film (100 µm thick) can be morphed into different shapes simply by varying the motifs of the photomasks.
A near‐infrared‐responsive gold nanorod/liquid crystal elastomer film is prepared, demonstrating excellent photothermal performance with fast actuation and recovery speed, cyclability, and the ability to achieve multiple shapes (both symmetric and asymmetric) from a single film with monodomain alignment of the liquid crystal director field through spatial modulation of the projected light to the film.
Strategies for obtaining materials that respond to external stimuli by changing shape are of intense interest for the replacement of traditional actuators. Here, a strategy that enables programmable, ...multiresponsive actuators that use either visible light or electric current to drive shape change in composites comprising carbon nanotubes (CNTs) in liquid crystal elastomers (LCEs) is presented. In the nanocomposites, the CNTs function not only in the traditional roles of mechanical reinforcement and enhancers of thermal and electrical conductivity but also serve as an alignment layer for the LCEs. By controlling the orientation, location, and quantity of layers of CNTs in LCE/CNT composites, programmed, patterned actuators are built that respond to visible light or electrical current. Photothermal LCE/CNT film actuators undergo fast shape change, within 1.2 s using 280 mW cm−2 light input, and complex, programmed localized deformations. Furthermore, twisting LCE/CNT composite films into a fiber increases uniaxial muscle stroke and work capacity for electrothermal actuation, thereby enabling about 12% actuation strain and 100 kJ m−3 of work capacity in response to an applied DC voltage of 15.1 V cm−1.
Programmable, multiresponsive liquid crystal elastomer/carbon nanotube (CNT) composites that change shape and accomplish work in response to optical or electrical stimuli are described. By designing the orientation and location of layers of CNT sheets, the stimulus response of the composite is programmed to provide complex macroscopic actuation.
3D printable and reconfigurable liquid crystal elastomers (LCEs) that reversibly shape‐morph when cycled above and below their nematic‐to‐isotropic transition temperature (TNI) are created, whose ...actuated shape can be locked‐in via high‐temperature UV exposure. By synthesizing LCE‐based inks with light‐triggerable dynamic bonds, printing can be harnessed to locally program their director alignment and UV light can be used to enable controlled network reconfiguration without requiring an imposed mechanical field. Using this integrated approach, 3D LCEs are constructed in both monolithic and heterogenous layouts that exhibit complex shape changes, and whose transformed shapes could be locked‐in on demand.
Reconfigurable liquid crystal elastomer (LCE) actuators that can reversibly shape‐morph prior to locking into their actuated shape upon exposure to UV light are synthesized and printed. Their director alignment is programmed by 3D printing, while light‐triggered activation of dynamic bonds within the LCE network facilitates their transition to a desired locked‐in state.
Liquid crystal elastomer (LCE) is a newly emerging soft actuating material that has been extensively explored for building novel soft robots and diverse active devices, thanks to its large actuation ...stress and strain, high work density, and versatile actuation modes. However, there have also been several widely recognized limitations of LCE-based actuators for practical applications, including slow response and narrow range of operation temperature. Herein, we develop fluid-driven disulfide LCE actuators through facile laminate manufacturing enabled by a dynamic bond exchange reaction. Because of the merits of the active heating/cooling mechanism of the fluidic structure, this newly developed disulfide LCE actuator can generate large cyclic actuation at a frequency around 1 Hz and can operate in a wide range of temperatures. The unique combination of the fluidic structure design and the dynamic covalent bonds in the elastomer has also enabled the full recyclability and self-repairability of the actuator. Using the newly developed actuator as building block, we further constructed soft robotic systems that can realize manipulating and programmable movement. The design principle demonstrated in the current work opens a promising avenue for exploring more novel applications of LCE-based soft actuators.
•A new light-fueled self-oscillating buckling and postbuckling disk is originally developed.•Two motion regimes of static regime and self-buckling regime are discovered.•The critical conditions for ...triggering self-buckling are calculated for different system parameters.•Results aid the design and control of self-oscillating buckling and postbuckling of the LCE disk.
Self-oscillating systems can absorb energy from steady environment to maintain continuous movements without the aid of extra controller. Different from the existing abundant self-oscillating systems, self-buckling has the advantages of sudden energy explosion and large displacement, and has potential application in the fields of jumping robots, rescue, military industries, mechano-logics and so on. However, it is a challenging task in avoiding the tendency of reaching thermodynamic equilibrium for a self-oscillating system. In this paper, we creatively develop a self-oscillating liquid crystal elastomer (LCE) disk, which is capable of buckling continuously and periodically under steady illumination. Based on nonlinear plate theory and dynamic LCE model, a nonlinear dynamic model of the self-buckling LCE disk is formulated. By series expansions and Runge-Kutta method, the dynamic buckling and postbuckling of the LCE disk under steady illumination is numerically calculated. The LCE disk under steady illumination can develop into two motion regimes: the static regime and the self-buckling regime, including alternating and unidirectional self-buckling regimes. The self-buckling of the disk can be triggered by controlling several key system parameters. In addition, the frequency and amplitude of the self-buckling can also be modulated by these parameters. The self-buckling LCE disk broadens the design ideas in the fields of new robots, energy conversion, and biomimetic.
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Liquid crystal elastomers (LCEs) are an attractive platform for dynamic shape‐morphing due to their ability to rapidly undergo large deformations. While recent work has focused on patterning the ...director orientation field to achieve desired target shapes, this strategy cannot be generalized to material systems where high‐resolution surface alignment is impractical. Instead of programming the local orientation of anisotropic deformation, an alternative strategy for prescribed shape‐morphing by programming the magnitude of stretch ratio in a thin LCE sheet with constant director orientation is developed here. By spatially patterning the concentration of gold nanoparticles, uniform illumination leads to gradients in photothermal heat generation and therefore spatially nonuniform deformation profiles that drive out‐of‐plane buckling of planar films into predictable 3D shapes. Experimentally realized shapes are shown to agree closely with both finite element simulations and geometric predictions for systems with unidirectional variation in deformation magnitude. Finally, the possibility to achieve complex oscillatory motion driven by uniform illumination of a free‐standing patterned sheet is demonstrated.
Light‐driven shape‐morphing via spatially patterned photothermal deformation of liquid crystal elastomers is demonstrated. Distinct from shape prescription via modulation of the director orientation, a general method for patterning deformation profiles in monodomain elastomers with a unidirectional director field is presented. A model for prescribing Gaussian curvature via continuous deformation profiles is presented and validated with experiments and finite element analysis.
Traditional hard robots often require complex motion‐control systems to accomplish various tasks, while applications of soft‐bodied robots are limited by their low load‐carrying capability. Herein, a ...hybrid tensegrity robot composed of both hard and soft materials is constructed, mimicking the musculoskeletal system of animals. Employing liquid crystal elastomer–carbon nanotube composites as artificial muscles in the tensegrity robot, it is demonstrated that the robot is extremely deformable, and its multidirectional locomotion can be entirely powered by light. The tensegrity robot is ultralight, highly scalable, has high load capacity, and can be precisely controlled to move along different paths on multiterrains. In addition, the robot also shows excellent resilience, deployability, and impact‐mitigation capability, making it an ideal platform for robotics for a wide range of applications.
Inspired by the musculoskeletal system of animals, a tensegrity robot, composed of stiff rods and soft artificial muscle fibers, is constructed. The robot is ultralight, highly scalable, has a high load capacity, and can be precisely controlled to move along different paths on multiterrains. It also shows excellent resilience, deployability, and impact‐mitigation capability.
Stimuli‐responsive and active materials promise radical advances for many applications. In particular, soft magnetic materials offer precise, fast, and wireless actuation together with versatile ...functionality, while liquid crystal elastomers (LCEs) are capable of large reversible and programmable shape‐morphing with high work densities in response to various environmental stimuli, e.g., temperature, light, and chemical solutions. Integrating the orthogonal stimuli‐responsiveness of these two kinds of active materials could potentially enable new functionalities and future applications. Here, magnetic microparticles (MMPs) are embedded into an LCE film to take the respective advantages of both materials without compromising their independent stimuli‐responsiveness. This composite material enables reconfigurable magnetic soft miniature machines that can self‐adapt to a changing environment. In particular, a miniature soft robot that can autonomously alter its locomotion mode when it moves from air to hot liquid, a vine‐like filament that can sense and twine around a support, and a light‐switchable magnetic spring are demonstrated. The integration of LCEs and MMPs into monolithic structures introduces a new dimension in the design of soft machines and thus greatly enhances their use in applications in complex environments, especially for miniature soft robots, which are self‐adaptable to environmental changes while being remotely controllable.
A liquid crystal elastomer material with embedded ferromagnetic microparticles takes advantage of both magnetic and thermal stimuli‐responsiveness. Such a monolithic soft material enables reconfigurable magnetic soft miniature machines that self‐adapt to changing environmental conditions. The hybrid material introduces a multi‐modal actuation and physical intelligence capability for wireless soft machines.
Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable and rapid actuation capabilities. Recent progress has been made ...on direct ink writing (DIW) or Digital Light Processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, a novel method to 4D print freestanding LCEs on‐the‐fly by using laser‐assisted DIW with an actuation strain up to −40% is proposed. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one‐step additive process. Various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW‐printed functionally freestanding LCEs with the DLP‐printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices.
A novel hybrid 4D printing method, which integrates laser‐assisted direct ink writing and Digital Light Processing, is developed to fabricate freestanding liquid crystal elastomers (LCEs) “on‐the‐fly” with optional structural or removable materials. Various architectures, including hybrid active lattices, active tensegrities, loading‐bearing actuators, and spatial LCE lattices, can be successfully fabricated.
A strip of a liquid crystal elastomer doped with a near‐infrared dye with one side crosslinked monodomain and the other crosslinked polydomain along the thickness behaves like a multifunctional ...photoactuator without the need for a support. A flat strip with two ends fixed on substrate surface forms a moving bump under laser scanning, which can be used as light‐fueled conveyor to transport an object. Cutting off and laser scanning the bump with two free ends makes a soft and flexible millimeter‐scale crawler that can not only move straight and climb an inclined surface, but also undergo light‐guided turning to right or left as a result of combined out‐of‐plane and in‐plane actuation. Based on the self‐shadowing mechanism, with one end of the strip fixed on substrate surface, it can execute a variety of autonomous arm‐like movements under constant laser illumination, such as bending–unbending and twisting, depending on the laser incident angles with respect to the strip actuator.
Jack of all trades: A photocrosslinkable liquid‐crystal polymer doped with a near‐infrared (NIR) dye acts as a multitasking soft actuator. It can be made to act as light‐driven walking belt for object transportation, a micro‐crawler capable of turning in its movement, and a self‐sustained oscillating arm.
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