Selective Decrosslinking in Liquid Crystal Polymer Actuators for Optical Reconfiguration of Origami and Light‐Fueled Locomotion

The ability to optically reconfigure an existing actuator of a liquid crystal polymer network (LCN) so that it can display a new actuation behavior or function is highly desired in developing materials for soft robotics applications. Demonstrated here is a powerful approach relying on selective polymer chain decrosslinking in a LCN actuator with uniaxial LC alignment. Using an anthracene‐containing LCN, spatially controlled optical decrosslinking can be realized through photocleavage of anthracene dimers under 254 nm UV light, which alters the distribution of actuation (crosslinked) and non‐actuation (decrosslinked) domains and thus determines the actuation behavior upon order‐disorder phase transitions. Based on this mechanism, a single actuator having a flat shape can be reconfigured in an on‐demand manner to exhibit reversible shape transformation such as self‐folding into origami three‐dimensional structures. Moreover, using a dye‐doped LCN actuator, a light‐fueled microwalker can be optically reconfigured to adopt different locomotion behaviors, changing from moving in the laser scanning direction to moving in the opposite direction.     

In-situ polymerization for mechanical strong composite actuators based on anisotropic wood and thermoresponsive polymer

Stimuli-responsive hydrogels hold an irreplaceable statue in intelligent actuation materials because of their reversible stretchability and excellent biocompatibility. However, the poor mechanical performance and complicated fabrication process of anisotropic structures severely limit their further applications.Herein, we report a high-strength thermoresponsive wood-PNIPAM composite hydrogel actuator with complex deformations, through a simple in-situ polymerization. In this composite hydrogel a...     

Liquid-Crystalline Soft Actuators with Switchable Thermal Reprogrammability

Thermal reprogrammability is essential for new-generation large dry soft actuators, but the realization sacrifices the favored actuation performance. The contradiction between thermal reprogrammability and stability hampers efforts to design high-performance soft actuators to be robust and thermally adaptable. Now, a strategy has been developed that relies on repeatedly switching on/off thermal reprogrammability in liquid-crystalline elastomer (LCE) actuators to resolve this problem. By post-synthesis swelling, a latent siloxane exchange reaction can be induced in the common siloxane LCEs (switching on), enabling reprogramming into on-demand 3D-shaped actuators; by switching off the dynamic network by heating, actuation stability is guaranteed even at high temperature (180 °C). Using partially black-ink-patterned LCEs, selectively switching off reprogrammability allows integration of completely different actuation modes in one monolithic actuator for more delicate and elaborate tasks.     

Liquid‐Crystalline Soft Actuators with Switchable Thermal Reprogrammability

Thermal reprogrammability is essential for new‐generation large dry soft actuators, but the realization sacrifices the favored actuation performance. The contradiction between thermal reprogrammability and stability hampers efforts to design high‐performance soft actuators to be robust and thermally adaptable. Now, a strategy has been developed that relies on repeatedly switching on/off thermal reprogrammability in liquid‐crystalline elastomer (LCE) actuators to resolve this problem. By post‐synthesis swelling, a latent siloxane exchange reaction can be induced in the common siloxane LCEs (switching on), enabling reprogramming into on‐demand 3D‐shaped actuators; by switching off the dynamic network by heating, actuation stability is guaranteed even at high temperature (180 °C). Using partially black‐ink‐patterned LCEs, selectively switching off reprogrammability allows integration of completely different actuation modes in one monolithic actuator for more delicate and elaborate tasks.     

Springtail-inspired Light-driven Soft Jumping Robots Based on Liquid Crystal Elastomers with Monolithic Three-leaf Panel Fold Structure

Jump is an important form of motion that enables animals to escape from predators, increase their range of activities, and better adapt to the environment. Inspired by springtails, we describe a light-driven soft jumping robot based on a double-folded liquid crystal elastomer (LCE) ribbon actuator with a monolithic three-leaf panel fold structure. This robot can achieve remarkable jumping height, jumping distance, and maximum take-off velocity, of up to 87 body length (BL), 65 BL, and 930 BL s⁻¹, respectively, under near-infrared light irradiation. Further, it is possible to control the height, distance, and direction of jump by changing the size and crease angle of the double-folded LCE ribbon actuators. These robots can efficiently jump over obstacles and can jump continuously, even in complex environments. Our simple design strategy improves the performance of jumping actuators and we expect it to have a wide-ranging impact on the strength, continuity, and adaptability of future soft robots.     

Thermoplastic Dielectric Elastomer of Triblock Copolymer with High Electromechanical Performance

Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single‐component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene‐b‐butyl acrylate‐b‐styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g^–1 within the excitation frequency range of 300–800 Hz.     

Electroactive-paper actuator made with cellulose/NaOH/urea and sodium alginate

In an earlier work we reported the discovery of cellulose as a smart material that can be used in sensors and actuators. While the cellulose-based Electro-Active Paper (EAPap) actuator has many merits – lightweight, dry condition, biodegradability, sustainability, large displacement output and low actuation voltage – its performance is sensitive to humidity. We report here on an EAPap made with a cellulose and sodium alginate that produces its maximum displacement at a lower humidity level than the earlier one. To fabricate this EAPap, we dissolved cellulose fibers into a aqueous solution of NaOH/urea. Sodium alginate (0, 5 or 10% by weight) was then added to this cellulose solution. The solution was cast into a sheet and hydrolyzed to form a wet cellulose-sodium alginate blend film. After drying, a bending EAPap actuator was made by depositing thin gold electrodes on both sides of it. The performance of the EAPap actuator was then evaluated in terms of free displacement and blocked force with respect to the actuation frequency, activation voltage and content of sodium alginate. The actuation principle is also discussed.     

响应性交联液晶高分子仿生致动器的研究进展

交联液晶高分子兼具液晶取向有序性和交联聚合物熵弹性等特点,能够以动态可调节和可逆的方式来模仿生物体的行为,在仿生器件、柔性机器人、智能表面、生物医药等领域具有良好的应用前景.本综述总结了近几年智能响应性交联液晶高分子在仿生致动器方面的研究进展,从响应性交联液晶高分子的结构和驱动机理出发,讨论了响应性交联液晶高分子的合成工艺、制备技术和成型方法,以及响应性交联液晶高分子对光、热、磁、湿度的响应.此外,介绍了响应性交联液晶高分子致动器在柔性机器人、人工肌肉、微流体运输等领域的应用.最后,对响应性交联液晶高分子的发展前景进行了展望.这项工作主要讨论了响应性交联液晶高分子,旨在为具有新颖功能和更有挑战性的智能微型致动器提供新的设计思路.     

电机械聚合物人工肌肉材料的研究进展

模拟肌肉组织进行信息传递、能量转换、传动的人工肌肉驱动器成为新材料研发焦点。智能聚合物可以对外界刺激发生响应,产生形变,是制备人工肌肉的良好材料,已被广泛地用于机器人与智能机械系统,成为众多肌肉驱动器中的研究重点。本文主要总结电机械聚合物人工肌肉材料的研究进展,论述了静电作用、电热驱动、水/湿度驱动三种驱动方式的工作机理和研究进展,分析了聚合物人工肌肉材料驱动器发展过程中受到限制的关键因素,并对未来人工肌肉材料研究提出展望。     

Polypyrrole stretchable actuators

Here, we report a simple way to prepare stretchable polypyrrole (PPy)‐based actuator materials that can be operated over a wide dynamic strain range and generate useable actuation displacements and pressures. The stretchable actuators were prepared as a laminated composite of PPy and a gold‐coated roughened rubber sheet. By manipulating the corrugated surface of the rubber substrate, the stretchability of PPy was greatly improved. Gold‐coated rubbers could be stretched to 30% without significant change in electrical resistance. The corrugated PPy/gold/rubber laminates successfully showed ～1% of actuation strain even when prestretched to 24%. The actuation strains were smaller than for similar free‐standing PPy films and a detailed analysis of the effects of corrugation and of the rubber substrate are presented to predict actuation strain under various prestretch strains. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Characterisation of torsional actuation in highly twisted yarns and fibres

Highly twisted oriented polymer fibres and carbon nanotube yarns show large scale torsional actuation from volume expansion that can be induced, for example, thermally or by electrochemical charging. When formed into spring-like coils, the torsional actuation within the fibre or yarn generates powerful tensile actuation per muscle weight. For further development of these coil actuators and for the practical application of torsional actuators, it is important to standardise methods for characterising both the torsional stroke (rotation) and torque generated. By analogy with tensile actuators, we here introduce a method to measure both the free stroke and blocked torque in a one-end-tethered fibre. In addition, the torsional actuation can be measured when operating against an externally applied torque (isotonic) and actuation against a return spring fibre (variable torque). A theoretical treatment of torsional actuation was formulated using torsion mechanics and evaluated using a commercially available highly-oriented polyamide fibre. Good agreement between experimental measurements and calculated values was obtained. The analysis allows the prediction of torsional stroke under any external loading condition based on the fundamental characteristics of the actuator: free stroke and stiffness.     

A Multifunctional Dye‐doped Liquid Crystal Polymer Actuator: Light‐Guided Transportation,Turning in Locomotion,and Autonomous Motion

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.     

A Multifunctional Dye‐doped Liquid Crystal Polymer Actuator: Light‐Guided Transportation,Turning in Locomotion,and Autonomous Motion

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.     

A naturally crosslinked chitosan based ionic actuator with cathode deflection phenomenon

In this communication, we introduce a chitosan polymer gel ionic actuator with dilute acid as electrolyte solution replacing ionic liquid. Interestingly, the switch not only produces obvious improvements in actuation performance, but the actuator bends towards the opposite direction. It presents a cathode deflection phenomenon instead of the usual anode deflection. Moreover, ion channels inside the electrolyte layer are obtained through a natural crosslinking treatment, so it allows an effective ions transportation inside the electrolyte layer.     

Dithienylethene-Based Single Molecular Photothermal Linear Actuator

By employing a mechanically controllable break junction technique, we have realized an ideal single molecular linear actuator based on dithienylethene (DTE) based molecular architecture, which undergoes reversible photothermal isomerization when subjected to UV irradiation under ambient conditions. As a result, open form (compressed, UV OFF) and closed form (elongated, UV ON) of dithienylethene-based molecular junctions are achieved. Interestingly, the mechanical actuation is achieved without changing the conductance of the molecular junction around the Fermi level over several cycles, which is an essential property required for an ideal single molecular actuator. Our study demonstrates a unique example of achieving a perfect balance between tunneling width and barrier height change upon photothermal isomerization, resulting in no change in conductance but a change in the molecular length, which results in mechanical actuation at the single molecular level.     

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo-Responsive Actuators

Arbitrary shape (re)programming is appealing for fabricating untethered shape-morphing photo-actuators with intricate configurations and features. We present re-programmable light-responsive thermoplastic actuators with arbitrary initial shapes through spray-coating of polyethylene terephthalate (PET) with an azobenzene-doped light-responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami-like folds and left- and right-handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area-specific actuation such as winding, unwinding and unfolding. By shape re-programming, the same sample can be re-designed and light-actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo-responsive actuators with highly tuneable geometries and actuation modes.     

本征导电聚合物的智能性

在化学掺杂或电化学掺杂过程中，性质发生可逆性变化的本征导电聚合物是一种潜在的智能材料，可望实现或部分实现传感、处理和执竽功能，适于制成电机执行器、智能窗、化学分离与释放体系、传感器和非线性光学器件等。     

Sensor–actuator system for dynamic chloride ion determination

Chloride is a crucial anion for various analytical applications from biological to environmental applications. In order to measure the chloride ion concentration, a measurement system is needed which can detect this concentration for prolonged times reliably. Chronopotentiometry is a technique which does not need a long term stable reference electrode and is therefore very suitable for prolonged ion concentration measurements. As the used electrode might be fouled by reaction products, this work focuses on a chronopotentiometric approach with a separated sensing electrode (sensor) and actuating electrode (actuator). Both actuation and sensor electrode are made of Ag/AgCl. A constant current is applied to the actuator and will start the reaction between Ag and Clˉ, while the resulting Clˉ ion concentration change is observed through the sensor, which is placed close to the actuator. The time it takes to locally deplete the Clˉ ions is called transition time. Experiments were performed to verify the feasibility of this approach. The performed experiments show that the sensor detects the local concentration changes resulting from the current applied to the actuator. A linear relation between the Clˉ ion concentration and the square root of the transition time was observed, just as was predicted by theory. The calibration curves for different chips showed that both a larger sensor and a larger distance between sensor and actuator resulted in a larger time delay between the transition time detected at the actuator and the sensor.     

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

Arbitrary shape (re)programming is appealing for fabricating untethered shape‐morphing photo‐actuators with intricate configurations and features. We present re‐programmable light‐responsive thermoplastic actuators with arbitrary initial shapes through spray‐coating of polyethylene terephthalate (PET) with an azobenzene‐doped light‐responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami‐like folds and left‐ and right‐handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area‐specific actuation such as winding, unwinding and unfolding. By shape re‐programming, the same sample can be re‐designed and light‐actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo‐responsive actuators with highly tuneable geometries and actuation modes.