True Low‐Power Self‐Locking Soft Actuators

Natural double‐layered structures observed in living organisms are known to exhibit asymmetric volume changes with environmental triggers. Typical examples are natural roots of plants, which show unique self‐organized bending behavior in response to environmental stimuli. Herein, light‐ and electro‐active polymer (LEAP) based actuators with a double‐layered structure are reported. The LEAP actuators exhibit an improvement of 250% in displacement and hold an object three times heavier as compared to that in the case of conventional electro‐active polymer actuators. Most interestingly, the bending motion of the LEAP actuators can be effectively locked for a few tens of minutes even in the absence of a power supply. Further, the self‐locking LEAP actuators show a large and reversible bending strain of more than 2.0% and require only 6.2 mW h cm^?2 of energy to hold an object for 15 min at an operating voltage of 3 V. These novel self‐locking soft actuators should find wide applicability in artificial muscles, biomedical microdevices, and various innovative soft robot technologies.     

Soft Actuators for Small‐Scale Robotics

This review comprises a detailed survey of ongoing methodologies for soft actuators, highlighting approaches suitable for nanometer‐ to centimeter‐scale robotic applications. Soft robots present a special design challenge in that their actuation and sensing mechanisms are often highly integrated with the robot body and overall functionality. When less than a centimeter, they belong to an even more special subcategory of robots or devices, in that they often lack on‐board power, sensing, computation, and control. Soft, active materials are particularly well suited for this task, with a wide range of stimulants and a number of impressive examples, demonstrating large deformations, high motion complexities, and varied multifunctionality. Recent research includes both the development of new materials and composites, as well as novel implementations leveraging the unique properties of soft materials.     

Light‐Directed Liquid Manipulation in Flexible Bilayer Microtubes

Flexible microfluidic systems have potential in wearable and implantable medical applications. Directional liquid transportation in these systems typically requires mechanical pumps, gas tanks, and magnetic actuators. Herein, an alternative strategy is presented for light‐directed liquid manipulation in flexible bilayer microtubes, which are composed of a commercially available supporting layer and the photodeformable layer of a newly designed azobenzene‐containing linear liquid crystal copolymer. Upon moderate visible light irradiation, various liquid slugs confined in the flexible microtubes are driven in the preset direction over a long distance due to photodeformation‐induced asymmetric capillary forces. Several light‐driven prototypes of parallel array, closed‐loop channel, and multiple micropump are established by the flexible bilayer microtubes to achieve liquid manipulation. Furthermore, an example of a wearable device attached to a finger for light‐directed liquid motion is demonstrated in different gestures. These unique photocontrollable flexible microtubes offer a novel concept of wearable microfluidics.     

3D Printing of Liquid Crystal Elastomeric Actuators with Spatially Programed Nematic Order

Liquid crystal elastomers (LCEs) are soft materials capable of large, reversible shape changes, which may find potential application as artificial muscles, soft robots, and dynamic functional architectures. Here, the design and additive manufacturing of LCE actuators (LCEAs) with spatially programed nematic order that exhibit large, reversible, and repeatable contraction with high specific work capacity are reported. First, a photopolymerizable, solvent‐free, main‐chain LCE ink is created via aza‐Michael addition with the appropriate viscoelastic properties for 3D printing. Next, high operating temperature direct ink writing of LCE inks is used to align their mesogen domains along the direction of the print path. To demonstrate the power of this additive manufacturing approach, shape‐morphing LCEA architectures are fabricated, which undergo reversible planar‐to‐3D and 3D‐to‐3D′ transformations on demand, that can lift significantly more weight than other LCEAs reported to date.     

Biomimetic Locomotion of Electrically Powered “Janus” Soft Robots Using a Liquid Crystal Polymer

Oriented liquid crystal networks (LCNs) can undergo reversible shape change at the macroscopic scale upon an order–disorder phase transition of the mesogens. This property is explored for developing soft robots that can move under external stimuli, such as light in most studies. Herein, electrically driven soft robots capable of executing various types of biomimetic locomotion are reported. The soft robots are composed of a uniaxially oriented LCN strip, a laminated Kapton layer, and thin resistive wires embedded in between. Taking advantage of the combined attributes of the actuator, namely, easy processing, reprogrammability, and reversible shape shift between two 3D shapes at electric power on and off state, the concept of a “Janus” soft robot is demonstrated, which is built from a single piece of the material and has two parts undergoing opposite deformations simultaneously under a uniform stimulation. In addition to complex shape morphing such as the movement of oarfish and sophisticated devices like self‐locking grippers, electrically powered “Janus” soft robots can accomplish versatile locomotion modes, including crawling on flat surfaces through body arching up and straightening down, crawling inside tubes through body stretching and contraction, walking like four‐leg animals, and human‐like two‐leg walking while pushing a load forward.     

Self-Assembled Microactuators Using Chiral Liquid Crystal Elastomers

Materials that undergo reversible changes in form typically require top-down processing to program the microstructure of the material. As a result, it is difficult to program microscale, 3D shape-morphing materials that undergo non-uniaxial deformations. Here, a simple bottom-up fabrication approach to prepare bending microactuators is described. Spontaneous self-assembly of liquid crystal (LC) monomers with controlled chirality within 3D micromold results in a change in molecular orientation across thickness of the microstructure. As a result, heating induces bending in these microactuators. The concentration of chiral dopant is varied to adjust the chirality of the monomer mixture. Liquid crystal elastomer (LCE) microactuators doped with 0.05 wt% of chiral dopant produce needle-shaped actuators that bend from flat to an angle of 27.2 ± 11.3° at 180 °C. Higher concentrations of chiral dopant lead to actuators with reduced bending, and lower concentrations of chiral dopant lead to actuators with poorly controlled bending. Asymmetric molecular alignment inside 3D structure is confirmed by sectioning actuators. Arrays of microactuators that all bend in the same direction can be fabricated if symmetry of geometry of the microstructure is broken. It is envisioned that the new platform to synthesize microstructures can further be applied in soft robotics and biomedical devices.     

Tunable Photocontrolled Motions Using Stored Strain Energy in Malleable Azobenzene Liquid Crystalline Polymer Actuators

A new strategy for enhancing the photoinduced mechanical force is demonstrated using a reprocessable azobenzene‐containing liquid crystalline network (LCN). The basic idea is to store mechanical strain energy in the polymer beforehand so that UV light can then be used to generate a mechanical force not only from the direct light to mechanical energy conversion upon the trans–cis photoisomerization of azobenzene mesogens but also from the light‐triggered release of the prestored strain energy. It is shown that the two mechanisms can add up to result in unprecedented photoindued mechanical force. Together with the malleability of the polymer stemming from the use of dynamic covalent bonds for chain crosslinking, large‐size polymer photoactuators in the form of wheels or spring‐like “motors” can be constructed, and, by adjusting the amount of prestored strain energy in the polymer, a variety of robust, light‐driven motions with tunable rolling or moving direction and speed can be achieved. The approach of prestoring a controllable amount of strain energy to obtain a strong and tunable photoinduced mechanical force in azobenzene LCN can be further explored for applications of light‐driven polymer actuators.     

含环氧键的液晶高分子改性环氧树脂的研究

利用自制含有环氧健的液晶高分子对环氧树脂／芳香胺固化体系进行改性并对样品进行各种测试。对比了改性前后环氧树脂的性能,发现含环氧健的液晶高分子能显著提高环氧树脂的韧性,同时耐热性也有较大程度地改善采用SEM分析了改性体系的断面结构。     

Continuous Flow Microfluidic Production of Arbitrarily Long Tubular Liquid Crystal Elastomer Peristaltic Pump Actuators

While liquid crystal elastomers (LCEs) are ideal materials for soft-robotic actuators, filling the role of muscle and shape-defining material simultaneously, it is non-trivial to give them ground state shapes beyond simple sheets or fibers. Here tubular LCE actuators scalable to arbitrary length are produced using a continuous three-phase coaxial flow microfluidic process. By pumping an oligomeric precursor solution between inner and outer aqueous phases in a cylindrically symmetric nested capillary set-up, and by reducing the interfacial tension to negligible values using surfactants adapted to each phase, the tubular liquid flow is stabilized over distances more than 200 times the diameter or 2000 times the thickness. In situ photocrosslinking of the middle phase turns it into an LCE network that is flow-aligned by the shear gradient over the phase. The reversible actuation of the tubes upon heating yields a reduction of the interior space, pumping out enclosed fluid, and the relaxation upon cooling leads to the fluid being sucked back in. By moving a local heat source along the tube, it acts as a peristaltic pump. It is proposed that the tubes could, pending functionalization for light-triggered actuation, function as active synthetic vasculature in biological contexts.