Mechanical Chameleon through Dynamic Real-Time Plasmonic Tuning

The development of camouflage methods, often through a general resemblance to the background, has recently become a subject of intense research. However, an artificial, active camouflage that provides fast response to color change in the full-visible range for rapid background matching remains a daunting challenge. To this end, we report a method, based on the combination of bimetallic nanodot arrays and electrochemical bias, to allow for plasmonic modulation. Importantly, our approach permits real-time light manipulation readily matchable to the color setting in a given environment. We utilize this capability to fabricate a biomimetic mechanical chameleon and an active matrix display with dynamic color rendering covering almost the entire visible region

Mechanical Chameleon through Dynamic Real-Time Plasmonic Tuning

The development of camouflage methods, often through a general resemblance to the background, has recently become a subject of intense research. However, an artificial, active camouflage that provides fast response to color change in the full-visible range for rapid background matching remains a daunting challenge. To this end, we report a method, based on the combination of bimetallic nanodot arrays and electrochemical bias, to allow for plasmonic modulation. Importantly, our approach permits real-time light manipulation readily matchable to the color setting in a given environment. We utilize this capability to fabricate a biomimetic mechanical chameleon and an active matrix display with dynamic color rendering covering almost the entire visible region

Simplified Synthesis of Fluoride-Free Ti₃C₂T_<i>x</i> via Electrochemical Etching toward High-Performance Electrochemical Capacitors

MXenes have been intensively studied for electrochemical energy storage and other applications. However, time-consuming multistep procedures involving hypertoxic HF or alike are utilized in conventional synthesis methods of MXenes. Besides, −F terminal functional groups inevitably exist in these MXenes, detrimental to supercapacitor and battery performances. Herein, we develop a facile and time-saving electrochemical etching method to synthesize F-free and Cl-containing Ti3C2Tx in a mixed LiOH and LiCl aqueous solution with an etching efficiency of 92.2%. During the synthesis, sonification alone is able to delaminate Ti3C2Tx without using any hazardous organic intercalant. The obtained delaminated Ti3C2Tx flakes are ∼3.8 μm in lateral size and ∼3.9 nm in thickness, and can be stable in an aqueous dispersion for at least 15 days. The filtrated Ti3C2Tx film is 20.5 MPa in tensile strength, 13.4 GPa in Young’s modulus, and 1663 S cm–1 in electrical conductivity, and exhibits specific capacitances of 323.7 F g–1, 1.39 F cm–2, and 1160 F cm–3 for supercapacitors. Also, a flexible zinc-ion hybrid capacitor with energy density values of 20.8 mWh cm–3 and 249.9 μWh cm–2 is assembled by using the Ti3C2Tx film as the cathode, and can maintain almost all its capacity under bending

Ultrafast Self-Healing Nanocomposites via Infrared Laser and Their Application in Flexible Electronics

The continuous evolution toward flexible electronics with mechanical robust property and restoring structure simultaneously places high demand on a set of polymeric material substrate. Herein, we describe a composite material composed of a polyurethane based on Diels–Alder chemistry (PU-DA) covalently linked with functionalized graphene nanosheets (FGNS), which shows mechanical robust and infrared (IR) laser self-healing properties at ambient conditions and is therefore suitable for flexible substrate applications. The mechanical strength can be tuned by varying the amount of FGNS and breaking strength can reach as high as 36 MPa with only 0.5 wt % FGNS loading. On rupture, the initial mechanical properties are restored with more than 96% healing efficiency after 1 min irradiation time by 980 nm IR laser. Especially, this is the highest value of healing efficiency reported in the self-healable materials based on DA chemistry systems until now, and the composite exhibits a high volume resistivity up to 5.6 × 10¹¹ Ω·cm even the loading of FGNS increased to 1.0 wt %. Moreover, the conductivity of the broken electric circuit which was fabricated by silver paste drop-cast on the healable composite substrate was completely recovered via IR laser irradiating bottom substrate mimicking human skin. These results demonstrate that the FGNS-PU-DA nanocomposite can be used as self-healing flexible substrate for the next generation of intelligent flexible electronics

Electrodeposition of Co(OH)₂ Improving Carbonized Melamine Foam Performance for Compressible Supercapacitor Application

In the development of commercial wearable electronic devices with improved mechanical and electrochemical performance, flexible supercapacitors can retain their original properties even under and during recovery from various mechanical deformations and have caused considerable attention because of their outstanding mechanical and electrochemical performance. In this work, a carbonized melamine foam /Co­(OH)2 (CMF/Co­(OH)2) compressible electrode material with a three-dimensional interconnected network structure was prepared by high-temperature carbonization and electrochemical deposition for developing a flexible supercapacitor. In the CMF/Co­(OH)2 compressible material, Co­(OH)2 nanosheets were vertically deposited on the CMF fiber surface with significantly increased specific surface area, illustrating a volumetric capacitance of 2.51 F/cm3 at 5 mA/cm3. Particularly, the CMF/Co­(OH)2 material delivers a remarkable compression performance with 97.80% volumetric capacitance retention in 60% compression strain. Moreover, we assembled an asymmetrical all-solid compressible supercapacitor based on CMF/Co­(OH)2 and surveyed its electrochemical performance to investigate the applicability of the compressible electrode material, and it has been demonstrated that two devices in series can drive a red light-emitting diode and work properly even under different compressions. These wonderful electrochemical and compression performances enable CMF/Co­(OH)2 to be a favorable compressible electrode material in flexible supercapacitors, expanding the application fields of flexible supercapacitors

Electrodeposition of Co(OH)₂ Improving Carbonized Melamine Foam Performance for Compressible Supercapacitor Application

In the development of commercial wearable electronic devices with improved mechanical and electrochemical performance, flexible supercapacitors can retain their original properties even under and during recovery from various mechanical deformations and have caused considerable attention because of their outstanding mechanical and electrochemical performance. In this work, a carbonized melamine foam /Co­(OH)2 (CMF/Co­(OH)2) compressible electrode material with a three-dimensional interconnected network structure was prepared by high-temperature carbonization and electrochemical deposition for developing a flexible supercapacitor. In the CMF/Co­(OH)2 compressible material, Co­(OH)2 nanosheets were vertically deposited on the CMF fiber surface with significantly increased specific surface area, illustrating a volumetric capacitance of 2.51 F/cm3 at 5 mA/cm3. Particularly, the CMF/Co­(OH)2 material delivers a remarkable compression performance with 97.80% volumetric capacitance retention in 60% compression strain. Moreover, we assembled an asymmetrical all-solid compressible supercapacitor based on CMF/Co­(OH)2 and surveyed its electrochemical performance to investigate the applicability of the compressible electrode material, and it has been demonstrated that two devices in series can drive a red light-emitting diode and work properly even under different compressions. These wonderful electrochemical and compression performances enable CMF/Co­(OH)2 to be a favorable compressible electrode material in flexible supercapacitors, expanding the application fields of flexible supercapacitors

Controlled Triphenylphosphine Reactivity for Epoxy Resin Cure by Transition-Metal β‑Diketonates

Cure kinetics control of epoxy resins is critical for the realization of many structures and processes and is often manipulated by catalyst design. We here show an example of switchable Lewis base catalytic activity through ligand-controlled metal coordination. Divalent first-row transition-metal (Co, Ni, Cu, Zn) β-diketonates with methyl or trifluoromethyl end groups have found distinguished thermal latent curing behaviors in triphenylphosphine (TPP)-catalyzed epoxy resins, namely, a deceleration pattern for metal acetylacetonates (acac2) and an inhibition pattern for metal hexafluoroacetylacetonates (6Facac2). Comparative analysis exposed the major initiation mechanism as phosphine attack on epoxide rings, where the phosphine reactivity was regulated by metal coordination whose strength depends on the original diketone ligands. TPP further stabilized the metal chelates and suppressed their dissociation. Feed ratio studies of Co­(II) chelates revealed an equilibrium built upon TPP, metal chelate, and the formed passivated complex through numerical analysis. Further, temperature dependence of the equilibrium constants suggested a reversed metal-base affinity evolution of the two chelates during heating, which determines the equivalent TPP concentration. Chemical and thermal characterizations on the formed complexation states identified structural changes during high-temperature treatment and, along with density functional theory (DFT) calculation, verified the Co–P binding energy that marks the TPP “effectiveness” in each stage to catalyze epoxy cure. It was found that the competition between incoming phosphine and original diketone ligands, depending on the basicity of the latter, dictates the initial relative affinity between metal and phosphine, while beyond phosphine ligand stabilization, the diketone ligand dynamics at elevated temperatures were accompanied by the respective Co–P affinity change. Across different metals, the deviation from the “natural order” in metal-phosphine affinity can also be qualitatively understood from the ligand competition concept, where the same ligand effects on the field stabilization schemes are expected as the distinctions caused by ligand fluorination were consistent throughout d7–d10 metal cations. The knowledge gained from this work could benefit future design of thermal latent catalysts and shed light on the capability of Lewis base reactivity control through adjusting transition-metal coordination spheres

High-Strength, Tough, Fatigue Resistant, and Self-Healing Hydrogel Based on Dual Physically Cross-Linked Network

Hydrogels usually suffer from low mechanical strength, which largely limit their application in many fields. In this Research Article, we prepared a dual physically cross-linked hydrogel composed of poly­(acrylamide-<i>co</i>-acrylic acid) (PAM-<i>co</i>-PAA) and poly­(vinyl alcohol) (PVA) by simple two-steps methods of copolymerization and freezing/thawing. The hydrogen bond-associated entanglement of copolymer chains formed as cross-linking points to construct the first network. After being subjected to the freezing/thawing treatment, PVA crystalline domains were formed to serve as knots of the second network. The hydrogels were demonstrated to integrate strength and toughness (1230 ± 90 kPa and 1250 ± 50 kJ/m³) by the introduction of second physically cross-linked network. What̀s more, the hydrogels exhibited rapid recovery, excellent fatigue resistance, and self-healing property. The dynamic property of the dual physically cross-linked network contributes to the excellent energy dissipation and self-healing property. Therefore, this work provides a new route to understand the toughness mechanism of dual physically cross-linked hydrogels, hopefully promoting current hydrogel research and expanding their applications

Water-Assisted Transformation of Aluminum Alloys to Ceramic Nanowires and Aerogels

Ceramic nanowires (NWs) and their-based aerogels hold great promise for manufacturing and applications of polymer nanocomposites with otherwise unattainable mechanical and thermal properties. Unfortunately, conventional routes for the synthesis of ceramic NWs commonly suffer from the use of costly or toxic chemicals, low production rate, and complex and expensive procedures. Here, we report on a water-assisted route for the cost-effective, scalable transformation of bulk aluminum–lithium alloys into ceramic alumina NWs and aerogels. In this study, we employ water as the intermediary solvent for dealloying to form monolithic porous Li-doped aluminum metal, which can then be converted to ultralong metal–organic NWs, then to hydroxide NWs after hydrolysis and finally to NW aerogels after freeze-drying. As a high-performance thermal interface material for electronic devices, the oxidized alumina NW aerogels infiltrated with epoxy show significantly improved thermal properties. Our study shows great potential for the scalable production of ceramic NWs using a low-cost and environmental-friendly route for various applications

Metal-Level Thermally Conductive yet Soft Graphene Thermal Interface Materials

Along with the technology evolution for dense integration of high-power, high-frequency devices in electronics, the accompanying interfacial heat transfer problem leads to urgent demands for advanced thermal interface materials (TIMs) with both high through-plane thermal conductivity and good compressibility. Most metals have satisfactory thermal conductivity but relatively high compressive modulus, and soft silicones are typically thermal insulators (0.3 W m–1 K–1). Currently, it is a great challenge to develop a soft material with the thermal conductivity up to metal level for TIM application. This study solves this problem by constructing a graphene-based microstructure composed of mainly vertical graphene and a thin cap of horizontal graphene layers on both the top and bottom sides through a mechanical machining process to manipulate the stacked architecture of conventional graphene paper. The resultant graphene monolith has an ultrahigh through-plane thermal conductivity of 143 W m–1 K–1, exceeding that of many metals, and a low compressive modulus of 0.87 MPa, comparable to that of silicones. In the actual TIM performance measurement, the system cooling efficiency with our graphene monolith as TIM is 3 times as high as that of the state-of-the-art commercial TIM, demonstrating the superior ability to solve the interfacial heat transfer issues in electronic systems