Ultrasensitive Biomimetic Skin with Multimodal and Photoelectric Dual-Signal Sensing.

Mimicking biological skin enabling direct, intelligent interaction between users and devices, multimodal sensing with optical/electrical (OE) output signals is urgently required. Owing to this, this work aims to logically design a stretchable OE biomimetic skin (OE skin), which can sensitively sense complex external stimuli of pressure, strain, temperature, and localization. The OE skin consists of elastic thin polymer-stabilized cholesteric liquid crystal films, an ion-conductive hydrogel layer, and an elastic protective membrane formed with thin polydimethylsiloxane. The as-designed OE skin exhibits customizable structural color on demand, good thermochromism, and excellent mechanochromism, with the ability to extend the full visible spectrum, a good linearity of over 0.99, fast response speed of 93 ms, and wide temperature range of 119 °C. In addition, the conduction resistance variation of ion-conductive hydrogel exhibits excellent sensing capabilities under pressure, stretch, and temperature, endowing a good linearity of 0.99998 (stretching from 0 to 150%) and high thermal sensitivity of 0.86% per °C. Such an outstanding OE skin provides design concepts for the development of multifunctional biomimetic skin used in human-machine interaction and can find wide applications in intelligent wearable devices and human-machine interactions.

Michael Addition Inducing Self-Assembly to Construct Mechanochromic BP Film.

Liquid crystalline blue phase (BP) with 3D cubic nanostructure has attracted much interest in the fields of photonic crystals due to their unique optical properties and the ability to control the flow of light. However, there remains a challenge for simultaneously achieving self-assembly and mechanochromic response of soft 3D cubic nanostructures. Herein, a scalable strategy for the preparation of soft 3D cubic nanostructured films using oligomerization of the Michael addition reaction, which can induce the assembly of double-twisted cylinders for collective replication, remodeling, recombination, and growth, with a phase transition from BPII to BPI, and to chiral nematic phase, is presented. The prepared BP patterns can be obtained by Michael addition oligomerization reaction and composite mask photopolymerization, which present distinct mechanochromic sensitive due to patterns derived from different BP state, and the pattern can be reversibly erased and recurred by mechanical force and temperature. The average domain size of BPII prepared using this strategy can achieve 96 µm, which is 2.5 times larger than that obtained using the conventional cooling approach. This work provides new insights into the self-assembly and selective chemochromism of functional materials and devices.

Rapid Yet Efficient Reduction of Graphene Oxide Triggered by Semi-Molten Metals.

Reduced graphene oxide (rGO) has garnered extensive attention as electrodes, sensors, and membranes, necessitating the efficient reduction of graphene oxide (GO) for optimal performance. In this work, a swift reduction of GO that involves bringing GO foam in contact with semi-molten metals like tin (Sn) and lithium (Li) is presented. These findings reveal that the electrical resistance of GO foam is significantly diminished by its interaction with these metals, even in dry air. Taking inspiration from this technique, Sn foil is employed to encase the GO foam, followed by a calcination in 15 vol% H2 /Ar environment at 235 °C to fabricate the rGO, which demonstrates a remarkably lower electrical resistivity of 0.42 Ω cm when compared to the chemically reduced GO via hydrazine hydrate (650 Ω cm). The reduction mechanism entails the migration of Sn on GO and its subsequent reaction with oxygen functional groups. SnO/Sn(OH)2 formed from the reaction can be subsequently reversed through reduction by H2 to Sn. Utilizing this rGO as the host material for a sulfur cathode, a lithium-sulfur battery is constructed that displays a specific capacity of 1146 mAh g-1 and maintains a capacity retention of 68.4% after 300 cycles at a rate of 0.2 C.

Effect of Carbonate Source on the Dehydrofluorination Process in Polyvinylidene Fluoride/Alkali Metal Carbonate Composites.

In this paper, Raman and X-ray photoelectron spectroscopies were applied to analyze compositional and structural variations of the generated activated carbon (AC), as induced by changing carbonate source in three different types of systems, PVDF/M2CO3 (M = Li, Na, and K). According to the variations of I D/I G and sp2/sp3 ratios, a strong dependence of the AC structure on the type and content of the initial carbonate was found, determined by practical dehydrofluorination reactions associated with oxygen incorporation in AC and side reactions, because of the property variation induced by the difference in the cation of the carbonate sources. This procedure clarified the process of PVDF dehydrofluorination and the formation of activated carbon, which helps to optimize the material performance of the percolative composite for flexible energy storage applications.

Design of Size-Controlled Sulfur Nanoparticle Cathodes for Lithium-Sulfur Aviation Batteries.

Lithium-sulfur (Li-S) battery has been considered as a strong contender for commercial aerospace battery, but the commercialization requires Ah-level pouch cells with both efficient discharge at high rates and ultra-high energy density. In this paper, the application of lithium-sulfur batteries for powering drones by using the cathode of highly dispersed sulfur nanoparticles with well-controlled particle sizes have been realized. The sulfur nanoparticles are prepared by a precipitation method in an eco-friendly and efficient way, and loaded on graphene oxide-cetyltrimethylammonium bromide by molecular grafting to realize a large-scale fabrication of sulfur-based cathodes with superior electrochemical performance. A button cell based on the cathode exhibits an excellent discharge capacity of 62.8 mAh cm-2 at a high sulfur loading of 60 mg cm-2 (i.e., 1046.7 mAh g-1 ). The assembled miniature pouch cell (PCmini) shows a discharge capacity of 130 mAh g-1 , while the formed Ah-level pouch cell (PCAh) achieves energy density of 307 Wh kg-1 at 0.3C and 92 Wh kg-1 at 4C. Especially, a four-axis propeller drone powered by the PC has successfully completed a long flight (>3 min) at high altitudes, demonstrating the practical applicability as aviation batteries.

Local chiral inversion of chiral nematic liquid crystals in cylinders.

On the basis of Landau-de Gennes theory and the finite-difference iterative method, the autonomic modulation of chiral inversion in a cylindrical cavity with degenerate planar anchoring is investigated. Under the applied helical twisting power (inversely related to the pitch P), a chiral inversion can be achieved due to the nonplanar geometry effect, and the inversion capacity rises with the increase of the helical twisting power. The combined effect of the saddle-splay K_{24} contribution (corresponding to the L_{24} term in Landau-de Gennes theory) and the helical twisting power are analyzed. It is found that the chiral inversion is more strongly modulated on the condition that the chirality of spontaneous twist is opposite to that of applied helical twisting power. Further, larger values of K_{24} will induce larger modulation of the twist degree and smaller modulation of the inverted region. The autonomic modulation of chiral inversion shows great potential for chiral nematic liquid crystal materials to be used in smart devices, such as light-controlled switches and nanoparticle transporters.

Origin of Surface Reconstruction in Lattice Oxygen Oxidation Mechanism Based-Transition Metal Oxides: A Spontaneous Chemical Process.

A fundamental understanding of surface reconstruction process is pivotal to developing highly efficient lattice oxygen oxidation mechanism (LOM) based electrocatalysts. Traditionally, the surface reconstruction in LOM based metal oxides is believed as an irreversible oxygen redox behavior, due to the much slower rate of OH- refilling than that of oxygen vacancy formation. Here, we found that the surface reconstruction in LOM based metal oxides is a spontaneous chemical reaction process, instead of an electrochemical reaction process. During the chemical process, the lattice oxygen atoms were attacked by adsorbed water molecules, leading to the formation of hydroxide ions (OH- ). Subsequently, the metal-site soluble atoms leached from the oxygen-deficient surface. This work also suggests that the enhancement of surface hydrophilicity could accelerate the surface reconstruction process. Hence, such a finding could add a new layer for the understanding of surface reconstruction mechanism.

Battery-like bismuth oxide anodes for soft-packed supercapacitors with high energy storage performance.

Bismuth compounds are of interest because of abundant reserves and high theoretical capacity for use as anodes in supercapacitors. In this work, bismuth oxycarbonate is synthesized by a hydrothermal method, and bismuth oxide is obtained by the subsequent calcination process, both of which possess high specific capacity. In particular, Bi2O3 possesses a specific capacity of 1178 F g-1 (1178 C g-1, 327 mA h g-1) at a current density of 1 A g-1, and still retains 94.9% capacity at 20 A g-1, indicating excellent rate capability. Furthermore, Ni(OH)2 is prepared with a specific capacity of 2447 F g-1 at 1 A g-1. Using Bi2O3 as the anode and Ni(OH)2 as the cathode, respectively, the soft-packed supercapacitors are assembled with a large voltage window of 1.75 V. The energy density is as high as 139.7 W h kg-1 at a power density of 874.8 W kg-1. Even at 18 000 W kg-1, the device retains an energy density of 94 W h kg-1. Connecting two devices in series as a power source can light up 88 light emitting diodes (LEDs) for 2 hours, and drive a tiny fan to run for 18 seconds. The work provides new ways for the practical application of supercapacitors.

Facile syntheses of Fe2O3-rGO and NiCo-LDH-rGO nanocomposites for high-performance electrochemical capacitors.

Faraday-type electrode materials and devices for electrochemical capacitors have been widely investigated. However, their applications are severely limited by the preparation method and cost of electrode materials. In this work, high-performance electrochemical capacitors were successfully assembled using Fe2O3-decorated reduced graphene oxide (rGO) nanocomposites and NiCo-Layered Double Hydroxides (LDH) as the anode and cathode, respectively. An easy and efficient approach (the modified precipitation method) for the large-scale fabrication was used to prepare Fe2O3 and NiCo-LDH, supported by rGO sheets, respectively. The anode material, Fe2O3-rGO, exhibited an excellent specific capacitance (Csp) of 1073 F g-1 at a current density of 1 A g-1 and a retention rate of 92 % at 10 A g-1, while the NiCo-LDH-rGO cathode material provided a Csp of 1850 F g-1 at 1 A g-1 and maintained 84 % at 10 A g-1. The effective combination of these electrodes for the NiCo-LDH-rGO//Fe2O3-rGO electrochemical capacitors resulted in an excellent energy density of 108 Wh/kg at a power density of 884 W/kg, with remarkable cycling stability (80 % after 1000 cycles at 10 A g-1). We believe that this work, including the proposed method and electrode materials, will advance the further development and commercialization of electrochemical capacitors.

Anisotropic porous designed polymer coatings for high-performance passive all-day radiative cooling.

Porous polymer radiative cooling coatings (PPCs) have attracted attention due to their ability of drawing and radiating heat from a hot object into the outer space, without any energy consumption. However, high performance of PPCs has yet to be achieved and the large-scale production of radiative cooling technology is still facing high cost and complex manufacturing constraints. Here, we propose a simple, inexpensive, scalable approach to fabricate anisotropic (P(VdF-HFP))ap PPCs (TPCs) by dissolution and diffusion between solvent and non-solvent-induced phase separation. By adjusting the porosity, pore size, and geometry, a sub-ambient temperature drop of ∼6.3°C in daytime and 10.1°C in night-time was achieved under a solar reflectance of 0.92 and an atmospheric window emittance of 0.96. A thermoelectric generator with an output voltage of almost zero reached 7 V/m2 after coating with TPCs. This could provide a convenient, economical, and environment-friendly way for PPCs materials toward efficient cooling and power generations.

Evolution analysis of FRIZZY PANICLE (FZP) orthologs explored the mutations in DNA coding sequences in the grass family (Poaceae).

FRIZZY PANICLE (FZP), an essential gene that controls spikelet differentiation and development in the grass family (Poaceae), prevents the formation of axillary bud meristems and is closely associated with crop yields. It is unclear whether the FZP gene or its orthologs were selected during the evolutionary process of grass species, which possess diverse spike morphologies. In the present study, we adopted bioinformatics methods for the evolutionary analysis of FZP orthologs in species of the grass family. Thirty-five orthologs with protein sequences identical to that of the FZP gene were identified from 29 grass species. Analysis of conserved domains revealed that the AP2/ERF domains were highly conserved with almost no amino acid mutations. However, species of the tribe Triticeae, genus Oryza, and C4 plants exhibited more significant amino acid mutations in the acidic C-terminus region. Results of the phylogenetic analysis showed that the 29 grass species could be classified into three groups, namely, Triticeae, Oryza, and C4 plants. Within the Triticeae group, the FZP genes originating from the same genome were classified into the same sub-group. When selection pressure analysis was performed, significant positive selection sites were detected in species of the Triticeae and Oryza groups. Our results show that the FZP gene was selected during the grass family's evolutionary process, and functional divergence may have already occurred among the various species. Therefore, researchers investigating the FZP gene's functions should take note of the possible presence of various roles in other grass species.

Template-Free Fabrication of Refractive Index Tunable Polysiloxane Coating Using Homogeneous Embedding Strategy: Application in High-Power Laser System.

A refractive index (RI) tunable polysiloxane coating was fabricated based on the cross-linked network structure embedded with mesoporous silica nanoparticles (MSNs), in which the MSNs were utilized to modulate the RI as well as to support the interior structure of the polysiloxane coating. The Si-O-Si inorganic backbone structure in combination with characteristics from the photopolymerization of active bonds produced the main cross-linked network structure, and controllable embedding of MSNs constructed the network-sphere structure. This approach eliminated the high-temperature post-treatment that was needed to remove the template, which ensures the safe application for temperature-sensitive laser crystal substrates and avoids coating structure collapse. In addition, degradation of the resulting coating can be minimized due to the similar chemical formation between MSN and polysiloxane coating. Hereby, a polysiloxane coating with expected spectral and laser damage-resistant properties can be obtained. This will facilitate the fabrication and application of a laser component with both high-transmission and high-flux capability for a high-power laser system.

Symmetric Continuously Tunable Photonic Band Gaps in Blue-Phase Liquid Crystals Switched by an Alternating Current Field.

Symmetric continuously tunable three-dimensional (3D) liquid photonic crystals have been investigated using self-organized blue-phase liquid crystal films. The photonic band gap in the overall visible spectrum can be tuned continuously, reversibly, and rapidly as the applied electric field changes. After driven by the applied field, four-time enhancement of the reflectivity results in more vivid reflection colors. A lasing emission of tuning working wavelength has been demonstrated by using the dye-doped blue-phase liquid crystal film. With the advantages of fast response speed, no alignment layer, large-scale electrically shift of the photonic band gap, and macro optical isotropy, this self-assembled soft material has many potential applications in high-performance reflective full-color display, 3D tunable lasers, and nonlinear optics.

Effect of component content variation on composition and structure of activated carbon in PVDF:K2CO3.

Percolative composites consisting of potassium carbonate dispersed in polyvinylidene fluoride (PVDF) polymeric matrix have shown high dielectric constant and electrical conductivity due to the formation of chemically activated carbon interfaces in the composite. In this paper, a series of PVDF/K2CO3 films with different component contents were prepared and investigated by Raman and X-ray photoelectron spectroscopies to clarify chemical composition, structure and formation mechanism of activated carbon. The results revealed the presence of a reaction loop to consume both constituent phases and the formation of sp2 carbon rings in the yielded activated carbon due to cross-linking dehydrofluorination of PVDF during thermal treatment. The sp2 content showed a non-linear dependence on K2CO3 content with the presence of an optimal value corresponding to the highest dielectric constant and electrical conductivity. This study thus can give a direction for future fabrication of PVDF/K2CO3 electrode materials for supercapacitors.

Fe substitution in urchin-like NiCo2O4 for energy storage devices.

A composite of NiCo2-x Fe x O4 was designed to investigate the effects of Fe substitution on its energy storage performance. Urchin-like products composed of nanowires were successfully synthesized through the hydrothermal method and calcinations. Scanning electron microscopy (SEM) images revealed that Fe substitution could reduce the diameter of the nanowires and hinder the urchin-like sphere construction. X-ray diffraction (XRD), energy dispersive X-ray mapping (EDS-mapping) and X-ray photoelectron spectroscopy (XPS) revealed the successful Fe substitution for Co. More importantly, the specific capacity could be largely improved from 359 C g-1 (826 F g-1) for x = 0 to 523 C g-1 (1188 F g-1) for x = 0.3 at 1 A g-1. Moreover, with x = 0.3, a specific capacity of 788 F g-1 could be maintained as the current density was increased to 20 A g-1. Asymmetric supercapacitors based on this compound exhibited an energy density of 26.6 W h kg-1 at a power density of 370 W kg-1.

Enhancement of Image Quality in LCD by Doping γ-Fe2O3 Nanoparticles and Reducing Friction Torque Difference.

Improving image sticking in liquid crystal display (LCD) has attracted tremendous interest because of its potential to enhance the quality of the display image. Here, we proposed a method to evaluate the residual direct current (DC) voltage by varying liquid crystal (LC) cell capacitance under the combined action of alternating current (AC) and DC signals. This method was then used to study the improvement of image sticking by doping γ-Fe2O3 nanoparticles into LC materials and adjusting the friction torque difference of the upper and lower substrates. Detailed analysis and comparison of residual characteristics for LC materials with different doping concentrations revealed that the LC material, added with 0.02 wt% γ-Fe2O3 nanoparticles, can absorb the majority of free ions stably, thereby reducing the residual DC voltage and extending the time to reach the saturated state. The physical properties of the LC materials were enhanced by the addition of a small amount of nanoparticles and the response time of doping 0.02 wt% γ-Fe2O3 nanoparticles was about 10% faster than that of pure LC. Furthermore, the lower absolute value of the friction torque difference between the upper and lower substrates contributed to the reduction of the residual DC voltage induced by ion adsorption in the LC cell under the same conditions. To promote the image quality of different display frames in the switching process, we added small amounts of the nanoparticles to the LC materials and controlled friction technology accurately to ensure the same torque. Both approaches were proven to be highly feasible.

Ni-Co layered double hydroxide on carbon nanorods and graphene nanoribbons derived from MOFs for supercapacitors.

In this study, carbon nanorods (CNR) and graphene nanoribbons (GNR) derived from metal-organic frameworks (MOFs) were first prepared by solvothermal method. Then, Ni-Co layered double hydroxide (LDH)/CNR and LDH/GNR composite materials for supercapacitors were synthesized using a facile co-precipitation method. With the help of GNR, the Ni-Co LDH/GNR composite material showed great specific capacity (1765 F g-1), rate performance (68% capacity retention when current density increased from 1 to 20 A g-1) and cycling stability (83% capacity retention after 2000 charge-discharge cycles at 5 A g-1). Furthermore, an asymmetric supercapacitor (ASC) with Ni-Co LDH/GNR as positive and activated carbon (AC) as negative electrodes was fabricated. The ASC device delivered a high energy density of 25.4 W h kg-1 at power density of 749 W kg-1 and exhibited excellent cycling stability (96% specific capacity retention after 5000 cycles).

Continuously adjustable period optical grating based on flexoelectric effect of a bent-core nematic liquid crystal in planar cells.

The structures of flexodomains, which are similar to optical gratings and can be controlled by the amplitude of applied voltage and temperature, were verified through polarizing microscopy and light diffraction techniques. The properties of the optical grating induced by a bent-core nematic liquid crystal in planar cells with varied cell gaps and pretilt angles were studied. The period of optical grating decreases with the increase in the amplitude of the applied voltage and pretilt angle. In addition, the period increases with the increase in cell gap and temperature. The period of optical grating has a linear relationship with temperature. The continuously adjustable period has the potential to become an important and extended application of optical grating.

Fast Switchable Dual-Model Grating by Using Polymer-Stabilized Sphere Phase Liquid Crystal.

We demonstrated a fast switchable dual-model grating based on a polymer-stabilized sphere phase liquid crystal. To form binary periodicity layers, the polymer-stabilized sphere phase liquid crystal precursor was sequence ultraviolet cured at an isotropic and sphere phase. This grating jointly modulated both the phase and the amplitude, had six times the diffraction efficiency of that fabricated with polymer-stabilized blue phase liquid crystal. Moreover, the dual-model tunable grating shown polarization-independent and submillisecond response time, which may hold a great potential application in diffractive optics.

Tailoring morphology of cobalt-nickel layered double hydroxide via different surfactants for high-performance supercapacitor.

Tailoring the morphology of cobalt-nickel layered double hydroxide (LDH) electrode material was successfully achieved via the process of cathodic electrodeposition by adding different surfactants (hexamethylenetetramine, dodecyltrimethylammonium bromide (DTAB) or cetyltrimethylammonium bromide). The as-prepared Co0.75Ni0.25(OH)2 samples with surfactants exhibited wrinkle-like, cauliflower-like or net-like structures that corresponded to better electrochemical performances than the untreated one. In particular, a specific capacitance of 1209.1 F g-1 was found for the cauliflower-like Co0.75Ni0.25(OH)2 electrode material using DTAB as the surfactant at a current density of 1 A g-1, whose structure boosted ion diffusion to present a good rate ability of 64% with a 50-fold increase in current density from 1 A g-1 to 50 A g-1. Accordingly, the asymmetric supercapacitor assembled by current LDH electrode and activated carbon electrode showed an energy density as high as 21.3 Wh kg-1 at a power density of 3625 W kg-1. The relationship between surfactant and electrochemical performance of the LDH electrode materials has been discussed.