Azo Polymer Janus Particles and Their Photoinduced, Symmetry-Breaking Deformation

We report the successful fabrication of photoresponsive Janus particles (JPs) composed of a methacrylate-based azo polymer (PAZO-ADMA) and poly­(methyl methacrylate) (PMMA). The JPs are obtained through microphase separation in a confined volume of the dispersed droplets, which incorporates the azo polymer and PMMA into one single particle in a core-compartmentalized manner. It is observed that several unique types of symmetry-breaking deformations are induced upon irradiation with a linearly polarized laser beam at 488 nm. The JPs with such properties are valuable for fundamental understanding and smart photofabrication in micrometer scale

Shape-Memory Actuation in Aligned Zirconia Nanofibers for Artificial Muscle Applications at Elevated Temperatures

Artificial muscle is one of the key technologies to accelerate the development of robotics, automation, and artificial-intelligence-embedded systems. This work aims to develop shape-memory ceramic (SMC) nanofiber-based coiled yarns for artificial muscle applications at elevated temperatures. Highly aligned SMC nanofiber (zirconia-based) yarns and springs have been successfully fabricated by electrospinning. The microstructure and tensile properties of the SMC nanofibers and the shape-memory actuation performance of the SMC yarns/springs have been characterized. A significant shape-memory effect with a recoverable strain of up to ∼5% and short recovery time (0.16 s) has been demonstrated in the SMC yarns at actuation temperatures of 328–388 °C. The SMC springs can lift up to 87 times their own weight when heated by a Bunsen burner, and the stroke is ∼3.9 mm. The SMC yarns/springs exhibit an output stress of 14.5–22.6 MPa, a work density of ∼15–20 kJ//m3, and a tensile strength of ∼100–200 MPa, which are much higher than those of human muscles and some other polymer-based artificial muscles. Benefiting from the advantages of large output stress, high tensile strength, high actuation temperatures, and fast response, the SMC nanofiber-based yarns/springs have a great potential to be used as artificial muscles at elevated temperatures

Breathable Metal–Organic Framework Enhanced Humidity-Responsive Nanofiber Actuator with Autonomous Triboelectric Perceptivity

Autonomous object manipulation and perception with environmental factor-triggered and self-powered actuation is one of the most attractive directions for developing next-generation soft robotics with a smart human-machine-environment interface. Humidity, as a sustainable energy source ubiquitous in the surrounding environment, can be used for triggering smart grippers. In this work, it is proposed that by contacts between the gripper and objects upon humidity-induced actuation, real-time distinguishable triboelectric signals can be generated to realize the humidity-driven object manipulation and identification. Herein, a thermo-modified electrospun polyvinylpyrrolidone/poly­(acrylic acid)/MIL-88A (T-PPM) nanofibrous film with micro-to-nano cross-scale porosity is developed, and a bilayer humidity-responsive actuator (T-HRA) was designed, mimicking the tamariskoid spikemoss to enhance the humidity-driven actuation. The breathing effect of MIL-88A and hierarchical porous structure of the T-PPM facilitate moisture diffusion and offer huge actuation (2.41 cm–1) with a fast response (0.084 cm–1 s–1). For autonomous object manipulation perception, T-PPM was verified as a tribo-positive material located between paper and silk. Accordingly, the T-HRA was demonstrated as a smart soft gripper that generates a different electric signal upon contact with objects of different material. This work proposes a concept of soft robots that are interactive with the environment for both autonomous object manipulation and information acquisition

Bridging Molecule Assisted Organic–Inorganic Interface Coassembly to Rationally Construct Metal Oxide Mesostructures

Mesostructured materials exhibit unique properties and attract great attention in many applications, but it is still challenging to synthesize mesostructured late transition metal oxides (e.g., ZnO and CuO) based on the conventional coassembly of surfactants and corresponding molecular precursors. In this work, a bridging molecule assisted coassembly strategy was developed by using ligand-capped crystalline ZnO and CuO nanocrystals (NCs) as a building block to assemble structure directing agent block copolymers (BCPs). Various mesostructured materials, including mesoporous metal oxide films and striped ellipsoidal particles, were obtained in elaborately controlled synthesis. Particularly, the structure variation under different conditions was systematically investigated by manipulating colloidal NCs–BCPs interface interactions during coassembly. Through calcination treatment to selectively decompose BCPs, a mesoporous metal oxide can be readily obtained. Taking the obtained mesoporous ZnO as an example, it exhibits excellent acetone sensing performance with high sensitivity and superior selectivity under a low working temperature (180 °C), because of the advantages of a high specific surface area (92 m2/g), rich active sites, and the unique NCs assembled framework. This bottom-up NCs–BCPs interface assembly approach can be well expanded to construct other mesostructure systems (e.g., noble metals and metal oxides–metal nanocrystal heterojunctions), serving as a universal methodology for the rational design of functional mesoporous materials with rich structural and compositional diversities

Breathable Metal–Organic Framework Enhanced Humidity-Responsive Nanofiber Actuator with Autonomous Triboelectric Perceptivity

Autonomous object manipulation and perception with environmental factor-triggered and self-powered actuation is one of the most attractive directions for developing next-generation soft robotics with a smart human-machine-environment interface. Humidity, as a sustainable energy source ubiquitous in the surrounding environment, can be used for triggering smart grippers. In this work, it is proposed that by contacts between the gripper and objects upon humidity-induced actuation, real-time distinguishable triboelectric signals can be generated to realize the humidity-driven object manipulation and identification. Herein, a thermo-modified electrospun polyvinylpyrrolidone/poly­(acrylic acid)/MIL-88A (T-PPM) nanofibrous film with micro-to-nano cross-scale porosity is developed, and a bilayer humidity-responsive actuator (T-HRA) was designed, mimicking the tamariskoid spikemoss to enhance the humidity-driven actuation. The breathing effect of MIL-88A and hierarchical porous structure of the T-PPM facilitate moisture diffusion and offer huge actuation (2.41 cm–1) with a fast response (0.084 cm–1 s–1). For autonomous object manipulation perception, T-PPM was verified as a tribo-positive material located between paper and silk. Accordingly, the T-HRA was demonstrated as a smart soft gripper that generates a different electric signal upon contact with objects of different material. This work proposes a concept of soft robots that are interactive with the environment for both autonomous object manipulation and information acquisition

Breathable Metal–Organic Framework Enhanced Humidity-Responsive Nanofiber Actuator with Autonomous Triboelectric Perceptivity

Autonomous object manipulation and perception with environmental factor-triggered and self-powered actuation is one of the most attractive directions for developing next-generation soft robotics with a smart human-machine-environment interface. Humidity, as a sustainable energy source ubiquitous in the surrounding environment, can be used for triggering smart grippers. In this work, it is proposed that by contacts between the gripper and objects upon humidity-induced actuation, real-time distinguishable triboelectric signals can be generated to realize the humidity-driven object manipulation and identification. Herein, a thermo-modified electrospun polyvinylpyrrolidone/poly­(acrylic acid)/MIL-88A (T-PPM) nanofibrous film with micro-to-nano cross-scale porosity is developed, and a bilayer humidity-responsive actuator (T-HRA) was designed, mimicking the tamariskoid spikemoss to enhance the humidity-driven actuation. The breathing effect of MIL-88A and hierarchical porous structure of the T-PPM facilitate moisture diffusion and offer huge actuation (2.41 cm–1) with a fast response (0.084 cm–1 s–1). For autonomous object manipulation perception, T-PPM was verified as a tribo-positive material located between paper and silk. Accordingly, the T-HRA was demonstrated as a smart soft gripper that generates a different electric signal upon contact with objects of different material. This work proposes a concept of soft robots that are interactive with the environment for both autonomous object manipulation and information acquisition

Robust Trioptical-State Electrochromic Energy Storage Device Enabled by Reversible Metal Electrodeposition

Reversible electrochemical mirror (REM) electrochromic devices based on reversible metal electrodeposition are exciting alternatives compared with conventional electrochromic because they offer electrochemical tunability in multiple optical states, long durability, and high contrast. Different from conventional electrochromic materials, of which the color change depends on the intercalation/deintercalation of ions into electrochromic films, the change in the optical states of REMs is based on the reversible electrodeposition and dissolution of metal. In this study, a REM electrochromic device with a Cu hybrid electrolyte composed of aqueous and nonaqueous components is proposed, which serves as an electrolyte reservoir that hosts Cu ions for reversible electrodeposition/dissolution. The hybrid electrolyte promotes the electrochemical reversibility of the Cu redox, an enhanced electrochromic performance, and a robust cycling stability of 5000 cycles (minor degradation of 4.71%). The investigation of the discharging/charging of the Cu hybrid REM device reveals that the Cl–/ClO– redox mechanism occurs at the cathode. Finally, an unprecedented dual-functional Cu hybrid REM energy storage device has been realized

Cementing Mesoporous ZnO with Silica for Controllable and Switchable Gas Sensing Selectivity

Nanostructured ZnO semiconductors as gas sensing materials have attracted great attention due to their high sensitivities, especially to reducing gases. However, ZnO based gas sensors lack controllable sensing selectivity. Herein, for the first time novel silica-cemented mesoporous ZnO materials with different contents of silica, high surface areas, and well-interconnected pores (∼29 nm) are synthesized through the evaporation-induced co-assembly (EICA) approach, and these amorphous ZnO materials exhibit controlled selectivity to ethanol or acetone. Strikingly, pure ZnO is found to exhibit better sensitivity to ethanol than that of acetone, while 2 wt % silica cemented mesoporous ZnO exhibits oppositely a selectively higher response to acetone than that of ethanol. In situ gas chromatograph–mass spectrum (GC-MS) analysis during the sensing process, in combination with intelligent gravimetric analyzer (IGA) measurement, reveals that such a preferential enhancement of acetone sensitivity by silica modification is mainly attributed to the dramatically improved adsorption of polar acetone molecules with a larger dipole moment of 2.88 D on the silica-cemented ZnO materials with higher surface polarity imparted by rich Zn–O–Si–OH bonds, and the acetone sensing process on pure ZnO and silica-cemented ZnO is found to experience a different reaction pathway

General Synthesis of Mixed Semiconducting Metal Oxide Hollow Spheres with Tunable Compositions for Low-Temperature Chemiresistive Sensing

Metal oxide hollow spheres (MOHSs) with multicomponent metal elements exhibit intriguing properties due to the synergistic effects of different components. However, it remains a great challenge to develop a general method to synthesize multicomponent MOHSs due to the different hydrolysis and condensation rates of precursors for different metal oxides. Herein, we demonstrate a general strategy for the controllable synthesis of MOHSs with up to five metal elements by decomposition of metal-phenolic coordination polymers (MPCPs), which are prepared by chelation of tannic acid with various metal ions. After calcination to burn out the organic component and induce heterogeneous contraction of MPCPs, a series of MOHSs with multishell structure, high specific surface area (55–171 m2/g), and crystalline mesoporous framework are synthesized, including binary (Fe–Co, Ni–Zn, and Ni–Co oxides), ternary (Ni–Co–Mn and Ni–Co–Zn oxides), and quinary (Ni–Co–Fe–Cu–Zn oxides) MOHSs. The gas sensing nanodevices based on quinary MOHSs show much higher response (10.91) than those based on single component toward 50 ppm of ethanol at 80 °C with the response/recovery time of 85/160 s. The quinary oxides sensor also displays high selectivity toward ethanol against other interfering gases (e.g., methanol, formadehyde, toluene, methane, and hydrogen) and long-term stability (∼94.0% after 4 weeks), which are extremely favorable for practical applications