Core-Shell Engineering of Conductive Fillers toward Enhanced Dielectric Properties: A Universal Polarization Mechanism in Polymer Conductor Composites

Recyclable and elastic highly thermally conductive epoxy-based composites with covalent-noncovalent interpenetrating networks

High-power electronic architectures and devices require elastic thermally conductive materials. The use of epoxy resin in thermal management is limited due to its rigidity. Here, based on epoxy vitrimer, flexible polyethylene glycol (PEG) chains are introduced into covalent adaptable networks to construct covalent-noncovalent interpenetrating networks, enabling the elasticity of epoxy resins. Compared to traditional silicone-based thermal interface materials, the newly developed elastic epoxy resin shows the advantages of reprocessability, self-healing, and no small molecule release. Results show that, even after being filled with boron nitride and liquid metal, the material maintains its resilience, reprocessability and self-healing properties. Leveraging these characteristics, the composite can be further processed into thin films through a repeated pressing-rolling technique that facilitates the forced orientation of the fillers. Subsequently, the bulk composites are reconstructed using a film-stacking method. The results indicate that the thermal conductivity of the reconstructed bulk composite reaches 3.66 W m-1 K-1, achieving a 68% increase compared to the composite prepared through blending. Due to the existence of covalent adaptable networks, the inorganic and inorganic components of the composite prepared in this work can be completely separated under mild conditions, realizing closed-loop recycling.

Chain-Like Semiconductive Fillers for Dielectric Enhancement and Loss Reduction of Polymer Composites

Dielectric loss is a crucial factor in determining the long-term endurance for security and energy loss of dielectric composites. Here, chain-like semiconductive fibers of titanium oxide, indium, and niobium-doped titanium oxide are used for enhancing the complex dielectric properties of a polymer through composite construction, which involves significant interface enhancements. The chain-like fibers significantly enhance the dielectric constant owing to the special morphology of the fillers and their interfacial polarization, especially at higher temperatures. The dielectric loss and electrical conductivity of the composites are substantially reduced across the entire investigated temperature range, achieved by passivating the fiber surface with an alumina shell using atomic layer deposition. The as-deposited alumina shell transformed from an amorphous to a crystalline phase through thermal annealing results in a porous shell and more effective suppression of the loss tangent and electrical conductivity. A plausible mechanism for loss suppression is associated with carrier movement along the surface of the fibers and bulk, leading to a higher loss tangent. The alumina shell blocks the carrier transport path, particularly at the interfaces, resulting in a reduced interfacial polarization contribution and energy storage loss. This study provides a method for inhibiting dielectric loss by fabricating fillers with special surfaces.

Enhanced Energy Storage in PVDF-Based Nanocomposite Capacitors through (00l)-Oriented BaTiO3 Single-Crystal Platelets

Flexible nanocomposite dielectrics with inorganic nanofillers exhibit great potential for energy storage devices in advanced microelectronics applications. However, high loading of inorganic nanofillers in the matrix results in an inhomogeneous electric field distribution, thereby hindering the improvement of the energy storage density (Ue) of the dielectrics. Herein, we proposed a strategy that utilized (00l)-oriented barium titanate (BT) single-crystal platelets to fabricate trilayered nanocomposite dielectrics for energy storage applications. The trilayered nanocomposites consisted of two high-permittivity layers of (Ta2O5, Al2O3) codoped TiO2 nanoparticles (Ta-Al@TiO2 nps) dispersed in a poly(vinylidene fluoride) (PVDF) matrix to facilitate large electric displacement and a middle layer of (00l)-oriented BT single-crystal platelets to provide high breakdown strength. Hence, the trilayered PVDF/Ta-Al@TiO2 nps/BT single-crystal platelet nanocomposite film attains an outstanding Ue of 16.9 J cm-3 at 370 kV mm-1, which is ∼625% higher than that of the single-layer PVDF/Ta-Al@TiO2 nps film. Finite element simulation further clarified that the successive inner layer of highly (00l)-oriented BT single-crystal platelets could effectively restrain the propagation of electrical treeing in trilayered nanocomposites. This research offers an effective approach for developing flexible dielectric capacitors with an excellent energy storage performance.

Soft Gel Filler Embedded Elastomer with Surfactant Improved Interface for Dielectric Elastomer Actuators

Stretchable materials are the foundation of dielectric actuators (DEAs) for artificial muscle. However, the inadequate dielectric constant of stretchable materials has always greatly limited the performance of artificial muscle. Recently, soft fillers have been proposed to improve the dielectric property and preserve the stretchability for softness, aiming to avoid the stiffening effect of traditional rigid fillers. As composites, an amount of interfacial region is generated, which remarkably affects composites' performance from dielectrics to mechanics. Herein, we demonstrate that the size effect, interfacial binding, and compatibility have a great impact on soft filler doped composites. Particularly, according to the liquid characteristics of soft fillers, we explore an interfacial modification method using surfactants. Composite breakdown strength is thus enhanced 2.2-fold from that in the control group due to the reduction of mismatch between fillers and matrix. Moreover, surfactants alleviate the well-known stiffening effect in small fillers. The area strain of the composites reaches 10.3 ± 0.4% at a low electric field of 7 MV/m, and a soft micropump is successfully assembled. These findings demonstrate a unique and combined interfacial influence of soft filler doped elastomer, which promotes the advancements of the dielectric elastomer artificial muscle.

Self-Assembled MXene@Fluorographene Hybrid for High Dielectric Constant and Low Loss Ferroelectric Polymer Composite Films

Modern electrical applications urgently need flexible polymer films with a high dielectric constant (εr) and low loss. Recently, the MXene-filled percolative composite has emerged as a potential material choice because of the promised high εr. Nevertheless, the typically accompanied high dielectric loss hinders its applications. Herein, a facile and effective surface modification strategy of cladding Ti3C2Tx MXene (T = F or O; FMX) with fluorographene (FG) via self-assembly is proposed. The obtained FMX@FG hybrid yields high εr (up to 108 @1 kHz) and low loss (loss tangent tan δ = 1.16 @ 1 kHz) in a ferroelectric polymer composite at a low loading level (the equivalent of 1.5 wt % FMX), which is superior to its counterparts in our work (e.g., FMX: εr = 104, tan δ = 10.71) and other studies. It is found that the FG layer outside FMX plays a critical role in both the high dielectric constant and low loss from experimental characterizations and finite element simulations. For one thing, FG with a high F/C ratio would induce a favorable structure of high β-phase crystallinity, extensive microcapacitor networks, and abundant interfacial dipoles in polymer composites that account for the high εr. For another, FG, as a highly insulating layer, can inhibit the formation of conductive networks and inter-FMX electron tunneling, which is responsible for conduction loss. The results demonstrate the potential of a self-assembled FMX@FG hybrid for high εr and low loss polymer composite films and offer a new strategy for designing advanced polymer composite dielectrics.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Constructing Deep Traps to Achieve Excellent Dielectric Properties in Crystal-Based HfO2/PEI Nanocomposite Films with Ultralow Filler Loadings

Mixing fillers featured with wide band gaps in polymers can effectively meet the requirement of higher energy storage densities. However, the fundamental relationship between the crystal structures of fillers and the dielectric properties of the corresponding nanocomposites is still unclear. Accordingly, we introduced ultralow contents of the synthesized cubic Hafnium dioxide (c-HfO2) or monoclinic Hafnium dioxide (m-HfO2) as deep traps into poly(ether imide) (PEI) to explore their effects on dielectric properties and the charge-blocking mechanism. m-HfO2/PEI showed better charge trapping due to the higher electron affinity and deeper trap energy. At room temperature, the 0.4 vol % m-HfO2/PEI maintains an ultralow dielectric loss of 0.008 while obtaining a dielectric constant twice that of pure PEI at 1 kHz, simultaneously outperforming in terms of leakage current density, breakdown strength (452 kV mm-1), discharge energy density (Ud, 5.03 J cm-3), charge-discharge efficiency (η, 92%), and dielectric thermal stability. At 125 °C, it exhibits a considerable Ud of 2.48 J cm-3 and a high η of 85% at 300 kV mm-1, surpassing the properties of pure PEI. This promising work opens up a new path for studying HfO2-derived dielectrics with unique crystal structures.

A Review of Polymer-Based Environment-Induced Nanogenerators: Power Generation Performance and Polymer Material Manipulations

Natural environment hosts a considerable amount of accessible energy, comprising mechanical, thermal, and chemical potentials. Environment-induced nanogenerators are nanomaterial-based electronic chips that capture environmental energy and convert it into electricity in an environmentally friendly way. Polymers, characterized by their superior flexibility, lightweight, and ease of processing, are considered viable materials. In this paper, a thorough review and comparison of various polymer-based nanogenerators were provided, focusing on their power generation principles, key materials, power density and stability, and performance modulation methods. The latest developed nanogenerators mainly include triboelectric nanogenerators (TriboENG), piezoelectric nanogenerators (PENG), thermoelectric nanogenerators (ThermoENG), osmotic power nanogenerator (OPNG), and moist-electric generators (MENG). Potential practical applications of polymer-based nanogenerator were also summarized. The review found that polymer nanogenerators can harness a variety of energy sources, with the basic power generation mechanism centered on displacement/conduction currents induced by dipole/ion polarization, due to the non-uniform distribution of physical fields within the polymers. The performance enhancement should mainly start from strengthening the ion mobility and positive/negative ion separation in polymer materials. The development of ionic hydrogel and hydrogel matrix composites is promising for future nanogenerators and can also enable multi-energy collaborative power generation. In addition, enhancing the uneven distribution of temperature, concentration, and pressure induced by surrounding environment within polymer materials can also effectively improve output performance. Finally, the challenges faced by polymer-based nanogenerators and directions for future development were prospected.

High Thermal Conductivity and Radiative Cooling Designed Boron Nitride Nanosheets/Silk Fibroin Films for Personal Thermal Management

The implementation of passive cooling strategies is crucial for transitioning from the current high-power- and energy-intensive thermal management practices to more environmentally friendly and carbon-neutral alternatives. Among the various approaches, developing thermal management materials with high thermal conductivity and emissivity for effective cooling of personal and wearable devices in both indoor and outdoor settings poses significant challenges. In this study, we successfully fabricated a cooling patch by combining biodegradable silk fibroin with boron nitride nanosheets. This patch exhibits consistent heat dissipation capabilities under different ambient conditions. Leveraging its excellent radiative cooling efficiency (Rsolar = 0.89 and εLWIR = 0.84) and high thermal conductivity (in-plane 27.58 W m-1 K-1 and out-plane 1.77 W m-1 K-1), the cooling patch achieves significant simulated skin temperature reductions of approximately 2.5 and 8.2 °C in outdoor and indoor conditions, respectively. Furthermore, the film demonstrates excellent biosafety and can be recycled and reused for at least three months. This innovative BNNS/SF film holds great potential for advancing the field of personal thermal management materials.

Core@Double-Shell Engineering of Zn Particles toward Elevated Dielectric Properties: Multiple Polarization Mechanisms in Zn@Znch@PS/PVDF Composites

Flexible dielectrics with large dielectric constant (ε') coupled with low loss are highly pursued in many applications. To bolster the ε' of raw Zn (zinc)/poly(vinylidene fluoride, PVDF) while maintaining pimping dielectric loss, in this study, the core@double-shell structured Zn@zinc carbonate (ZnCH)@polystyrene (PS) particles are first synthesized through a suspension polymerization of styrene, and then composited with PVDF to elevate the ε' and keep low loss of the composites. By optimizing the PS shells' thickness and tailoring the electrical resistivity of Zn@ZnCH@PS particles, both the slow inter-particle polarization and fast intra-particle polarization in the composites can be decoupled and synergistically tuned, thus, the Zn@ZnCH@PS/PVDF achieves a much higher ε' and lower dielectric loss, simultaneously, which far exceed the unmodified Zn/PVDF. Both experiment and theoretic calculation reveal that the double-shell ZnCH@PS not only induces and promotes multiple polarizations enhancing the composites' ε', especially at the optimized PS's thickness, but also maintains suppressed loss and conductivity thanks to their obvious barrier effect on long-range charge migration. The core@double-shell filler design strategy facilitates the development of polymer composites with desirable dielectric properties for applications in electronic and electrical power systems.

Synthesis of Hierarchical CF@Fe3O4 Fibers Decorated with MoS2 Layers Forming Core-Sheath Microstructure toward Tunable and Efficient Electromagnetic Wave Absorption

Hierarchical structural design has been verified as a feasible strategy to fabricate effective electromagnetic wave (EMW) absorbers, so we designed hierarchical core-sheath composites with magnetic particles and dielectric layers. In this work, a hierarchical structure of carbon fiber (CF)@Fe3O4@MoS2 (CPDF7-M) was prepared by introducing Fe3O4 and depositing MoS2 layers on the surface of fibers. Due to the synergistic effects from the CF@Fe3O4 increasing the conductive and magnetic loss and the outer MoS2 layers improving the impedance matching, the optimal reflection loss (RL) value was -63.1 dB at 2.7 mm and the effective absorption bandwidth (EAB) was 9.1 GHz covering the X and Ku band. Moreover, the EAB values were adjusted with a specific MoS2 loading at different thicknesses, which provided the necessary reference for the construction of efficient and flexible absorbers in the EMW absorption fields.

Recent Study Advances in Flexible Sensors Based on Polyimides

With the demand for healthy life and the great advancement of flexible electronics, flexible sensors are playing an irreplaceably important role in healthcare monitoring, wearable devices, clinic treatment, and so on. In particular, the design and application of polyimide (PI)-based sensors are emerging swiftly. However, the tremendous potential of PI in sensors is not deeply understood. This review focuses on recent studies in advanced applications of PI in flexible sensors, including PI nanofibers prepared by electrospinning as flexible substrates, PI aerogels as friction layers in triboelectric nanogenerator (TENG), PI films as sensitive layers based on fiber Bragg grating (FBG) in relative humidity (RH) sensors, photosensitive PI (PSPI) as sacrificial layers, and more. The simple laser-induced graphene (LIG) technique is also introduced in the application of PI graphitization to graphene. Finally, the prospect of PIs in the field of electronics is proposed in the review.

Effect of copper doping on plasmonic nanofilms for high performance photovoltaic energy applications

In the current era, alternative but environment-friendly sources of energy have gained attention to meet the growing energy demands. In particular, the focus of research has been solar energy and using it to fulfill energy demands. Solar energy is either directly converted into electrical energy or stored for later use. Solar cells are a practical way to turn solar energy into electrical energy. Various materials are being investigated to manufacture solar cell devices that can absorb a maximum number of photons present in sunlight. The present study reports thermally evaporated in situ Cu-doped SnS photon absorber thin films with tunable physical properties. This study mainly explored the effects of changing Cu concentrations on the physical features of light absorption of SnS thin films. The thin films were formed by simultaneous resistive heating of Cu and SnS powders on glass substrates at 150 °C. The X-ray diffraction patterns revealed pure SnS thin films having orthorhombic polycrystalline crystal structures oriented preferentially along the (111) plane. Raman spectroscopy confirmed this phase purity. Photoconductivity studies showed phase dependence on Cu content that improved with increasing concentrations of Cu. The optical bandgap energy was also found to be dependent on Cu content and was observed at 1.10-1.47 eV for SnS thin films with variation in the Cu content, i.e., 0-18%. According to the hot probe method, all films displayed p-type conductivity for the substitution of Cu metal atoms. These findings demonstrated that the prepared thin films are substantial candidates as low-cost, suitably efficient, thin-film solar cells featuring environmentally-friendly active layers that absorb sunlight.

In Situ Construction of High-Thermal-Conductivity and Negative-Permittivity Epoxy/Carbon Fiber@Carbon Composites with a 3D Network by High-Temperature Chemical Vapor Deposition

Modern highly integrated microelectronic devices are unable to dissipate heat over time, which greatly affects the operating efficiency and service life of electronic equipment. Constructing high-thermal-conductivity composites with 3D network structures is a hot research topic. In this article, carbon fiber felt (CFF) was prepared by airflow netting forming technology and needle punching combined with stepped heat treatment. Then, carbon-coated carbon fiber felt (C@CFF) with a three-dimensional network structure was constructed in situ by high-temperature chemical vapor deposition (CVD). Finally, high-temperature treatment was used to improve the degree of crystallinity of C@CFF and further enhance its graphitization. The epoxy (EP) composites were prepared by simple vacuum infiltration-molding curing. The test results showed that the in-plane thermal conductivity (K∥) and through-plane thermal conductivity (K⊥) of EP/C@CFF-2300 °C could reach up to 13.08 and 2.78 W/mK, respectively, where the deposited carbon content was 11.76 vol %. The in-plane thermal conductivity enhancement (TCE) of EP/C@CFF-2300 °C was improved by 6440 and 808% compared to those of pure EP and EP/CFF, respectively. The high-temperature treatment greatly provides an improvement in thermal conductivity for the in-plane and the through-plane. Infrared imaging showed excellent thermal management properties of the prepared epoxy composites. EP/C@CFF-2300 °C owned an in-plane AC conductivity of up to 0.035 S/cm at 10 kHz, and Lorentz-Drude-type negative permittivity behaviors were observed at the tested frequency region. The CFF thermally conductive composites prepared by the above method have a broad application prospect in the field of advanced thermal management and electromagnetics.

Progress of Polymer-Based Dielectric Composites Prepared Using Fused Deposition Modeling 3D Printing

Polymer-based dielectric composites are of great importance in advanced electronic industries and energy storage because of their high dielectric constant, good processability, low weight, and low dielectric loss. FDM (Fused Deposition Modeling) is a greatly accessible additive manufacturing technology, which has a number of applications in the fabrication of RF components, but the unavoidable porosity in FDM 3D-printed materials, which affects the dielectric properties of the materials, and the difficulty of large-scale fabrication of composites by FDM limit its application scope. This study's main focus is on how the matrix, filler, interface, and FDM 3D printing parameters influence the electrical properties of FDM-printed polymer-based dielectric composites. This review article starts with the fundamental theory of dielectrics. It is followed by a summary of the factors influencing dielectric properties in recent research developments, as well as a projection for the future development of FDM-prepared polymer-based dielectric composites. Finally, improving the comprehensive performance of dielectric composites is an important direction for future development.

Heterodimensional Structure Switching Multispectral Stealth and Multimedia Interaction Devices

Lightweight and flexible electronic materials with high energy attenuation hold an unassailable position in electromagnetic stealth and intelligent devices. Among them, emerging heterodimensional structure draws intensive attention in the frontiers of materials, chemistry, and electronics, owing to the unique electronic, magnetic, thermal, and optical properties. Herein, an intrinsic heterodimensional structure consisting of alternating assembly of 0D magnetic clusters and 2D conductive layers is developed, and its macroscopic electromagnetic properties are flexibly designed by customizing the number of oxidative molecular layer deposition (oMLD) cycles. This unique heterodimensional structure features highly ordered spatial distribution, with an achievement of electron-dipole and magnetic-dielectric double synergies, which exhibits the high attenuation of electromagnetic energy (160) and substantial improvement of dielectric loss tangent (≈200%). It can respond to electromagnetic waves of different bands to achieve multispectral stealth, covering visible light, infrared radiation, and gigahertz wave. Importantly, two kinds of ingenious information interaction devices are constructed with heterodimensional structure. The hierarchical antennas allow precise targeting of operating bands (S- to Ku- bands) by oMLD cycles. The strain imaging device with high sensitivity opens a new horizon for visual interaction. This work provides a creative insight for developing advanced micro-nano materials and intelligent devices.

Dielectric and energy storage properties of surface-modified BaTi0.89Sn0.11O3@polydopamine nanoparticles embedded in a PVDF-HFP matrix

In the most recent electronic and electric sectors, ceramic-polymer nanocomposites with high dielectric permittivity and energy density are gaining popularity. However, the main obstacle to improving the energy density in flexible nanocomposites, besides the size and morphology of the ceramic filler, is the low interfacial compatibility between the ceramic and the polymer. This paper presents an alternative solution to improve the dielectric permittivity and energy storage properties for electronic applications. Here, the poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix is filled with surface-modified BaTi0.89Sn0.11O3/polydopamine nanoparticles (BTS11) nanoparticles, which is known for exhibiting multiphase transitions and reaching a maximum dielectric permittivity at room temperature. BTS11 nanoparticles were synthesized by a sol-gel/hydrothermal method at 180 °C and then functionalized by polydopamine (PDA). As a result, the nanocomposites exhibit dielectric permittivity (εr) of 46 and a low loss tangent (tan δ) of 0.017 at 1 kHz at a relatively low weight fraction of 20 wt% of BTS11@PDA. This is approximately 5 times higher than the pure PVDF-HFP polymer and advantageous for energy storage density in nanocomposites. The recovered energy storage for our composites reaches 134 mJ cm-3 at an electric field of 450 kV cm-1 with a high efficiency of 73%. Incorporating PDA-modified BTS11 particles into the PVDF-HFP matrix demonstrates highly piezo-active regions associated with BTS11 particles, significantly enhancing functional properties in the polymer nanocomposites.

MOF-Derived Nitrogen-Doped Porous Carbon Polyhedrons/Carbon Nanotubes Nanocomposite for High-Performance Lithium-Sulfur Batteries

Nanocomposites that combine porous materials and a continuous conductive skeleton as a sulfur host can improve the performance of lithium-sulfur (Li-S) batteries. Herein, carbon nanotubes (CNTs) anchoring small-size (~40 nm) N-doped porous carbon polyhedrons (S-NCPs/CNTs) are designed and synthesized via annealing the precursor of zeolitic imidazolate framework-8 grown in situ on CNTs (ZIF-8/CNTs). In the nanocomposite, the S-NCPs serve as an efficient host for immobilizing polysulfides through physical adsorption and chemical bonding, while the interleaved CNT networks offer an efficient charge transport environment. Moreover, the S-NCP/CNT composite with great features of a large specific surface area, high pore volume, and short electronic/ion diffusion depth not only demonstrates a high trapping capacity for soluble lithium polysulfides but also offers an efficient charge/mass transport environment, and an effective buffering of volume changes during charge and discharge. As a result, the Li-S batteries based on a S/S-NCP/CNT cathode deliver a high initial capacity of 1213.8 mAh g-1 at a current rate of 0.2 C and a substantial capacity of 1114.2 mAh g-1 after 100 cycles, corresponding to a high-capacity retention of 91.7%. This approach provides a practical research direction for the design of MOF-derived carbon materials in the application of high-performance Li-S batteries.

Design of Polymer Nanodielectrics for Capacitive Energy Storage

Polymer nanodielectrics present a particularly challenging materials design problem for capacitive energy storage applications like polymer film capacitors. High permittivity and breakdown strength are needed to achieve high energy density and loss must be low. Strategies that increase permittivity tend to decrease the breakdown strength and increase loss. We hypothesize that a parameter space exists for fillers of modest aspect ratio functionalized with charge-trapping molecules that results in an increase in permittivity and breakdown strength simultaneously, while limiting increases in loss. In this work, we explore this parameter space, using physics-based, multiscale 3D dielectric property simulations, mixed-variable machine learning and Bayesian optimization to identify the compositions and morphologies which lead to the optimization of these competing properties. We employ first principle-based calculations for interface trap densities which are further used in breakdown strength calculations. For permittivity and loss calculations, we use continuum scale modelling and finite difference solution of Poisson's equation for steady-state currents. We propose a design framework for optimizing multiple properties by tuning design variables including the microstructure and interface properties. Finally, we employ mixed-variable global sensitivity analysis to understand the complex interplay between four continuous microstructural and two categorical interface choices to extract further physical knowledge on the design of nanodielectrics.

Dual Reversible Network Nanoarchitectonics for Ultrafast Light-Controlled Healable and Tough Polydimethylsiloxane-Based Composite Elastomers

It is highly desirable to develop polydimethylsiloxane (PDMS) elastomers with high self-healing efficiency and excellent mechanical properties. However, most self-healable materials reported to date still take several hours to self-heal and improving the self-healing property often comes at the expense of mechanical properties. Herein, a simple design strategy of dual reversible network nanoarchitectonics is reported for constructing ultrafast light-controlled healable (40 s) and tough (≈7.2 MJ m-3) PDMS-based composite elastomers. The rupture reconstruction of dynamic bonds and the reinforcement effect of carbon nanotubes (10 wt %) endowed our composite elastomer with excellent fracture toughness that originated from a good yield strength (≈1.1 MPa) and stretchability (≈882%). Moreover, carbon nanotubes can quickly and directly heat the damaged area of the composite to achieve its ultrafast repair with the assistance of dynamic polymer/filler interfacial interaction, greatly shortening the self-healing time (12 h). The self-healing performance is superior to that of reported self-healable PDMS-based materials. This novel strategy and the as-prepared supramolecular elastomer can inspire further various practical applications, such as remote anti-icing/deicing materials.

Design and characterization of molecular, crystal and interfacial structures of PVDF-based dielectric nanocomposites for electric energy storage

PVDF-based polymers with polar covalent bonds are next-generation dielectric materials for electric energy storage applications. Several types of PVDF-based polymers, such as homopolymers, copolymers, terpolymers and tetrapolymers, were synthesized by radical addition reactions, controlled radical polymerizations, chemical modifications or reduction with the monomers of vinylidene fluoride (VDF), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), hexafluoropropylene (HFP) and chlorotrifluoroethylene (CTFE). Owing to rich molecular structures and complicated crystal structures, PVDF-based dielectric polymers can show versatile dielectric polarization properties, including normal ferroelectrics, relaxor ferroelectrics, anti-ferroelectrics and linear dielectrics, which are beneficial for designing polymer films with high capacity and high charge-discharge efficiency for capacitor applications. Furthermore, to satisfy the requirements of practical high-capacity capacitors, the polymer nanocomposite method is another promising strategy to achieve high-capacitance dielectric materials by the addition of high-dielectric ceramic nanoparticles, moderate-dielectric nanoparticles (MgO, and Al₂O₃), high-insulation nanosheets (BN), etc. It is concluded with the current problems and future perspectives of interfacial engineering, such as core-shell strategies and hierarchical interfaces in polymer-based composite dielectrics for high-energy-density capacitor applications. In addition, an in-depth understanding of the roles of interfaces on the dielectric properties of nanocomposites can be achieved by indirect analysis techniques (theoretical simulation) and direct analysis techniques (scanning probe microscopy). Our systematic discussions on molecular, crystal and interfacial structures provide guidance for designing fluoropolymer-based nanocomposites for high-performance capacitor applications.

Recent Advances in Porous Carbon Materials as Electrodes for Supercapacitors

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors.

Carbon dots as specific fluorescent sensors for Hg2+ and glutathione imaging

Nitrogen-doped carbon dots (NCDs) have been constructed in which coal washing wastewater is used as carbon precursor, tryptophan is added for nitrogen doping and surface functional together with polyethylene glycol. The nitrogen doping and surface functional with electron rich groups resulted in excellent fluorescent properties regarding stability, reversibility, printability with high quantum yield which not only enable the NCDs as fluorescent ink for advanced message encryption, but also realize specific on-off-on fluorescent sensing of Hg2+ and GSH as solution, hydrogel and filter paper sensors. The NCDs had a linear range of 0.01-100 μM and a detection limit of 6.27 nM (RSD 0.33%) for Hg2+ and the NCDs@Hg2+ had a linear range of 0.01-60 μM and a detection limit of 3.53 nM (RSD 1.53%) for GSH in sensing studies with aqueous solutions. In addition, with the low cytotoxicity and good biocompatibility NCDs have been successfully used for imaging Hg2+ and GSH in living MG-63 cells. The presented NCDs recycle waste coal washing water into worthwhile material which can be implemented as promising anti-counterfeiting and message encryption candidates as well as effective Hg2+ and GSH sensing, tracking and removing tools in complicated environmental and biological systems.

Electromagnetic Response of Multistage-Helical Nano-Micro Conducting Polymer Structures and their Enhanced Attenuation Mechanism of Multiscale-Chiral Synergistic Effect

Nowadays, the rapidly development of advanced antidetection technology raises stringent requirements for microwave absorption materials (MAMs) to focus more attention on wider bandwidth, thinner thickness, and lower density. Adding magnetic medium to realize broadband absorption may usually result in the decline of service performance and accelerating corrosion of MAMs. Chiral MAMs can produce extra magnetic loss without adding magnetic medium due to the unique electromagnetic cross polarization effect. However, more efforts should be taken to furtherly promote efficient bandwidth of chiral MAMs and reveal attenuation mode and modulation method of chiral structure. Herein, a novel superhelical nano-microstructure based on chiral polyaniline and helical polypyrrole is successfully achieved via in situ polymerization strategy. The enhanced multiscale-chiral synergistic effect contributes to broaden effective absorption bandwidth, covering 8.6 GHz at the thickness of 3.6 mm, and the minimum reflection loss can reach -51.3 dB simultaneously. Besides, to further explain response modes and loss mechanism of superhelical nano-microstructures, the electromagnetic simulation and test analysis are applied together to reveal their synergistic enhancement attenuation mechanism. Taken together, this strategy gives a new thought of how to design, prepare, and optimize the hierarchical structure materials to achieving broadband and high-performance microwave absorption.

Interfacial Insight of Charge Transport in BaTiO3/Epoxy Composites

Space charge accumulation greatly influences the dielectric performance of epoxy composites under high voltage. It has been reported that nano-fillers can suppress the charge accumulation in the bulk of insulation materials. However, it is still unclear how the nano-fillers influence the charge distribution at the interface between the filler and polymeric matrix. In this work, the dielectric properties and the local dynamic charge mobility behavior at the interface of barium titanate/epoxy resin (BTO/EP) composites were investigated from both bulk and local perspectives based on the macroscopic test techniques and in-situ Kelvin probe force microscopy (KPFM) methods. Charge injection and dissipation behavior exhibited significant discrepancies at different interfaces. The interface between BTO and epoxy is easy to accumulates a negative charge, and nanoscale BTO (n-BTO) particles introduces deeper traps than microscale BTO (m-BTO) to inhibit charge migration. Under the same bias condition, the carriers are more likely to accumulate near the n-BTO than the m-BTO particles. The charge dissipation rate at the interface region in m-BTO/EP is about one order of magnitude higher than that of n-BTO/EP. This work offers experimental support for understanding the mechanism of charge transport in dielectric composites.

Significantly Suppressed Dielectric Loss and Enhanced Breakdown Strength in Core@Shell Structured Ni@TiO2/PVDF Composites

An insulating shell on the surface of conductive particles is vital for restraining the dielectric loss and leakage current of polymer composites. So as to inhibit the enormous loss and conductivity of pristine nickel (Ni)/poly(vinylidene fluoride)(PVDF) composites but still harvest a high dielectric permittivity (ε_r) when filler loading approaches or exceeds the percolation threshold (f_c), pristine Ni particles were covered by a layer of titanium dioxide (TiO₂) shell via a sol-gel approach, and then they were composited with PVDF. The impacts of the TiO₂ coating on the dielectric performances of the Ni/PVDF composites were explored as a function of the filler concentration, the shell thickness and frequency. In addition, the dielectric performances were fitted using the Havriliak-Negami (H-N) equation in order to further understand the TiO₂ shell's effect on polarization mechanism in the composites. The Ni@TiO₂/PVDF composites exhibit high ε_r and enhanced breakdown strength (E_b) but remarkably suppressed loss and conductivity when compared with pristine Ni/PVDF because the TiO₂ shell can efficiently stop the direct contact between Ni particles thereby suppressing the long-range electron transportation. Further, the dielectric performances can be effectively tuned through finely adjusting the TiO₂ shell' thickness. The resulting Ni@TiO₂/PVDF composites with high ε_r and E_b but low loss show appealing applications in microelectronics and electrical fields.

Lithium Vanadium Oxide/Graphene Composite as a Promising Anode for Lithium-Ion Batteries

Lithium vanadium oxide (Li₃VO₄, LVO) is a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity (394 mAh g^-1) and safe working potential (0.5-1.0 V vs. Li⁺/Li). However, its electrical conductivity is low which leads to poor electrochemical performance. Graphene (GN) shows excellent electrical conductivity and high specific surface area, holding great promise in improving the electrochemical performance of electrode materials for LIBs. In this paper, LVO was prepared by different methods. SEM results showed the obtained LVO by sol-gel method possesses uniform nanoparticle morphology. Next, LVO/GN composite was synthesized by sol-gel method. The flexible GN could improve the distribution of LVO, forming a high conductive network. Thus, the LVO/GN composite showed outstanding cycling performance and rate performance. The LVO/GN composite can provide a high initial capacity of 350.2 mAh g^-1 at 0.5 C. After 200 cycles, the capacity of LVO/GN composite remains 86.8%. When the current density increased from 0.2 C to 2 C, the capacity of LVO/GN composite only reduced from 360.4 mAh g^-1 to 250.4 mAh g^-1, demonstrating an excellent performance rate.