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.     

All‐Optical Control of Shape

Photoresponsive liquid crystal elastomers (LCEs) are a unique class of anisotropic materials capable of undergoing large‐scale, macroscopic deformations when exposed to light. Here, surface‐aligned, azobenzene‐functionalized LCEs are prepared via a radical‐mediated, thiol‐acrylate chain transfer reaction. A long‐lived, macroscopic shape deformation is realized in an LCE composed with an o‐fluorinated azobenzene (oF‐azo) monomer. Under UV irradiation, the oF‐azo LCE exhibits a persistent shape deformation for >72 h. By contrasting the photomechanical response of the oF‐azo LCE to analogs prepared from classical and m‐fluorinated azobenzene derivatives, the origin of the persistent deformation is clearly attributed to the underlying influence of positional functionalization on the kinetics of cis→trans isomerization. Informed by these studies and enabled by the salient features of light‐induced deformations, oF‐azo LCEs are demonstrated to undergo all‐optical control of shape deformation and shape restoration.     

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.     

Self‐Regulating Iris Based on Light‐Actuated Liquid Crystal Elastomer

The iris, found in many animal species, is a biological tissue that can change the aperture (pupil) size to regulate light transmission into the eye in response to varying illumination conditions. The self‐regulation of the eye lies behind its autofocusing ability and large dynamic range, rendering it the ultimate “imaging device” and a continuous source of inspiration in science. In optical imaging devices, adjustable apertures play a vital role as they control the light exposure, the depth of field, and optical aberrations of the systems. Tunable irises demonstrated to date require external control through mechanical actuation, and are not capable of autonomous action in response to changing light intensity without control circuitry. A self‐regulating artificial iris would offer new opportunities for device automation and stabilization. Here, this paper reports the first iris‐like, liquid crystal elastomer device that can perform automatic shape‐adjustment by reacting to the incident light power density. Similar to natural iris, the device closes under increasing light intensity, and upon reaching the minimum pupil size, reduces the light transmission by a factor of seven. The light‐responsive materials design, together with photoalignment‐based control over the molecular orientation, provides a new approach to automatic, self‐regulating optical systems based on soft smart materials.     

Superior Self‐Powered Room‐Temperature Chemical Sensing with Light‐Activated Inorganic Halides Perovskites

Hybrid halide perovskite is one of the promising light absorber and is intensively investigated for many optoelectronic applications. Here, the first prototype of a self‐powered inorganic halides perovskite for chemical gas sensing at room temperature under visible‐light irradiation is presented. These devices consist of porous network of CsPbBr₃ (CPB) and can generate an open‐circuit voltage of 0.87 V under visible‐light irradiation, which can be used to detect various concentrations of O₂ and parts per million concentrations of medically relevant volatile organic compounds such as acetone and ethanol with very quick response and recovery time. It is observed that O₂ gas can passivate the surface trap sites in CPB and the ambipolar charge transport in the perovskite layer results in a distinct sensing mechanism compared with established semiconductors with symmetric electrical response to both oxidizing and reducing gases. The platform of CPB‐based gas sensor provides new insights for the emerging area of wearable sensors for personalized and preventive medicine.     

Photoaligned Nanorod Enhancement Films with Polarized Emission for Liquid‐Crystal‐Display Applications

Semiconductor nanorods (NR) emit polarized light, which is expected to bring manifold benefits, in terms of brightness and color enhancement, for modern liquid‐crystal displays (LCD). In this regard, photoaligned nanorod enhancement films (NREF) for color and polarization conversion for LCD backlights are introduced here. The photoinduced anchoring forces, by the photoalignment layer, stimulate well‐ordered self‐assembly of NR in the thin polymer films. Green and red emitting NR with a quantum yield of ≈80% are aligned unidirectionally and in‐plane, showing a polarization ratio of >7:1 and a degree of polarization of >0.81. The photoalignment technique facilitates the fabrication of mixed and multiple stacked NREF for LCDs, which improves the color gamut and polarization efficiency, and is thus expected to increase the optical efficiency of conventional LCDs by ≈60%.     

A Self‐Powered and Flexible Organometallic Halide Perovskite Photodetector with Very High Detectivity

Flexible and self‐powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self‐powered and flexible PD based on the methylammonium lead iodide (CH₃NH₃PBI₃) perovskite is demonstrated. Such a self‐powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high‐quality CH₃NH₃PBI₃ perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 10¹³ Jones. In the self‐powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW^?1 cm^?2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self‐powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real‐world sensing capability, suggests a new direction for next‐generation optical communications, sensing, and imaging applications.     

Stretchable Thin‐Film Electrodes for Flexible Electronics with High Deformability and Stretchability

Flexible and stretchable electronics represent today's cutting‐edge electronic technologies. As the most‐fundamental component of electronics, the thin‐film electrode remains the research frontier due to its key role in the successful development of flexible and stretchable electronic devices. Stretchability, however, is generally more challenging to achieve than flexibility. Stretchable electronic devices demand, above all else, that the thin‐film electrodes have the capacity to absorb a large level of strain (>>1%) without obvious changes in their electrical performance. This article reviews the progress in strategies for obtaining highly stretchable thin‐film electrodes. Applications of stretchable thin‐film electrodes fabricated via these strategies are described. Some perspectives and challenges in this field are also put forward.