Higher efficiency, lower cost refrigeration is needed for both large and small scale cooling. Refrigerators using entropy changes during cycles of stretching or hydrostatically compression of a solid are possible alternatives to the vapor-compression fridges found in homes. We show that high cooling results from twist changes for twisted, coiled, or supercoiled fibers, including those of natural rubber, NiTi, and polyethylene fishing line. By using opposite chiralities of twist and coiling, supercoiled natural rubber fibers and coiled fishing line fibers result that cool when stretched. A demonstrated twistbased device for cooling flowing water provides a high cooling energy and device efficiency. Theory describes the axial and spring index dependencies of twist-enhanced cooling and its origin in a phase transformation for polyethylene fibers.Summary: Twist-exploiting mechanocaloric cooling is demonstrated for rubber fibers, fishing line fibers, and NiTi shape-memory wires.3

Artificial muscles triggered by light are of great importance, especially for the development of non-contact and remotely controlled materials. Common materials for synthesis of photoinduced artificial muscles typically rely on polymer-based photomechanical materials. Herein, we are able to prepare artificial muscles using a mixed-matrix membrane strategy to incorporate photomechanical molecular crystals with connective polymers (e.g. PVDF). The formed hybrid materials inherit not only the advantages of the photomechanical crystals, including faster light response, higher Young's modulus and ordered structure, but also the elastomer properties from polymers. This new type of artificial muscles demonstrates various muscle movements, including lifting objects, grasping objects, crawling and swimming, triggered by light irradiation. These results open a new direction to prepare light-driven artificial muscles based on molecular crystals.

Photothermal bimorph actuators are widely used for smart devices, which are generally operated in a room temperature environment, therefore a low temperature difference for actuation without deteriorating the performance is preferred. The strategy for the actuator is assembling a broadband‐light absorption layer for volume expansion and an additional water evaporation layer for cooling and volume shrinkage on a passive layer. The response time and temperature‐change‐normalized bending speed under NIR, white, and blue light illumination are at the same level of high performance, fast photothermal actuators based on polymer or polymer composites. The classical beam theory and finite element simulations are also conducted to understand the actuation mechanism of the actuator. A new type of light mill is designed based on a wing‐flapping mechanism and a light‐modulated frequency switch. A fast‐walking robot (with a speed of 26 mm s−1) and a fast‐and‐strong mechanical gripper with a large weight‐lifting ratio (≈2142), respectively, are also demonstrated.

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In recent years, significant progresses have been recorded in the development of soft actuators regarding the material and structural designs. [11,[13][14][15][16][17] Improved actuation speed was obtained by decreasing the response time of volume change; [9][10][11][18][19][20] and enhanced actuation force was realized by increasing the rigidity of the actuator material; [19,[21][22][23][24][25][26] and increased bending curvature was achieved by increasing the asymmetric volume change. [27,28] For example, fast response can be realized employing the following strategies, for example, by increasing absorption/desorption of vapor molecules by the actuator film, [18][19][20] or by increasing the shrinking of the film by photothermal-induced water-desorption, [9,10] or by increasing polymer volume expansion via the photothermal effect of carbon nanomaterials. [11] The bimorph actuators fabricated from soft materials (e.g., elastomers and hydrogels) commonly exhibit a larger bending curvature, [29][30][31] but lower actuation force and response rate compared with those fabricated from rigid materials. Contrarily, the rigidmaterial-based actuators can generate relatively faster actuation speed and larger force, [16,21,25] but smaller bending curvature compared to those fabricated from soft materials. Therefore, it is challenging to simultaneously achieve high actuation force and large bending curvature within a short response time.Until now, there are only a few successful designs of thinfilm jumping actuators by different delicate approaches. [9][10][11][12] Aida group reported a π-stacked carbon nitride polymer (CNP) thin film actuator exhibiting a tough, ultra-lightweight and highly anisotropic layered structure, which responded to the adsorption and desorption of a minute amount of water and is extremely rapid (50 ms by one curl). The film can jump 10-mmhigh on light irradiation by losing the adsorbed water. [10] Wang group reported graphene oxide (GO)/CNT bilayer actuator, where the GO layer allowed fast diffusion of water molecules and the aligned CNT layer imposed constrain. The actuator showed fast response (0.08 s) with large bending curvature, which demonstrated jumping actuation under photothermal induced water desorption from the GO layer. [9] Chen and coworkers prepared a jumping actuator by mimicking flicking finger motion, employing the rolled CNT/polydimethylsiloxane (PDMS) bilayer composite. The unique combination of loosely CNT network, good photo-thermal effect of CNT, and the large difference between thermal expansion coefficient between the two layers resulted in light-induced jumping up to five times higher than its own height. [11] Cai group reported a jumping actuator by mimicking the fruit fly larva, employing CNT/ liquid crystal elastomer (LCE) bilayer composite. Under light It is highly desirable to develop compact-and robust-film jumping robots that can withstand severe conditions. Besides, the demands for strong actuation force, large bending curvature in a short response time, and good e...

No abstract

Artificial muscles triggered by light are of great importance, especially for the development of non‐contact and remotely controlled materials. Common materials for synthesis of photoinduced artificial muscles typically rely on polymer‐based photomechanical materials. Herein, we are able to prepare artificial muscles using a mixed‐matrix membrane strategy to incorporate photomechanical molecular crystals with connective polymers (e.g. PVDF). The formed hybrid materials inherit not only the advantages of the photomechanical crystals, including faster light response, higher Young's modulus and ordered structure, but also the elastomer properties from polymers. This new type of artificial muscles demonstrates various muscle movements, including lifting objects, grasping objects, crawling and swimming, triggered by light irradiation. These results open a new direction to prepare light‐driven artificial muscles based on molecular crystals.

It is highly desirable to develop fiber materials with high strength and toughness while increasing fiber strength always results in a decrease in toughness. Spider silk is a natural fiber material with an excellent combination of high strength and toughness, which is produced from the spinning dope solution by gelation and drawing spinning process. This encourages people to prepare artificial fibers by mimicking the material, structure, and spinning of natural spider silk. In this review, we first summarized the preparation of artificial spider silk prepared via such a gelation process from different types of materials, including nonrecombinant proteins, recombinant proteins, polypeptides, synthetic polymers, and polymer nanocomposites. In addition, different spinning approaches for spinning artificial spider silk are also summarized. In the third section, some novel application scenarios of the artificial spider silk were summarized, such as artificial muscles, sensing, and smart fibers.