Excellent Dielectric Properties Research Articles

Highly Anisotropic Thermally Conductive Dielectric Polymer/Boron Nitride Nanotube Composites for Directional Heat Dissipation.

An ideal dielectric material for microelectronic devices requires a combination of high anisotropic thermal conductivity and low dielectric constant (ɛ') and loss (tan δ). Polymer composites of boron nitride nanotubes (BNNTs), which offer excellent thermal and dielectric properties, show promise for developing these dielectric polymer composites. Herein, a simple method for fabricating polymer/BNNT composites with high directional thermal conductivity and excellent dielectric properties is presented. The nanocomposites with directionally aligned BNNTs are fabricated through melt-compounding and in situ fibrillation, followed by sintering the fibrous nanocomposites. The fabricated nanocomposites show a significant enhancement in thermal properties, with an in-plane thermal conductivity (K‖) of 1.8 Wm-1K-1-a 450% increase-yielding a high anisotropy ratio (K‖/K⊥) of 36, a 1700% improvement over isotropic samples containing only 7.2 vol% BNNT. These samples exhibit a 120% faster in-plane heat dissipation compared to the through-plane within 2 s. Additionally, they display low ɛ'of ≈3.2 and extremely low tan δ of ≈0.014 at 1kHz. These results indicate that this method provides a new avenue for designing and creating polymer composites with enhanced directional heat dissipation properties along with high K‖, suitable for thermal management applications in electronic packaging, thermal interface materials, and passive cooling systems.

Development of copper-boron nitride core-shell structured fillers and surface treatment for thermally conductive composites

Core-shell structured copper-boron nitride (Cu@BN) spherical fillers were synthesized to fabricate thermally conductive composites. To enhance the interaction between the fillers and the matrix, polysilazane (PSZ) was coated on the surface of the filler. The resultant composite exhibited remarkable characteristics, including a substantial tensile strength of 32.36MPa, excellent electrical insulation properties, and impressive thermal conductivity of 3.47W/mK. When applied in a light-emitting diode (LED) application, the composite effectively managed heat, reducing the operating temperature by 34 °C. The epoxy/PSZ-Cu@BN composites hold great promise for improving thermal management in electronic devices.

In Situ Exsolution-Prepared Solid-Solution-Type Sulfides with Intracrystal Polarization for Efficient and Selective Absorption of Low-Frequency Electromagnetic Wave.

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid-solution-type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high-purity solid-solution-type sulfides is proposed based on solid-phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl-LDH/MIL-88A composite as a precursor, Fe0.8Co0.2S single-phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low-frequency region (2-6GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high-purity solid-solution-type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance.

Tailoring the physicochemical and dielectric properties of natural polymer using graphene nanoplatelet as filler

AbstractBio‐based flexible dielectric substrates have gained tremendous attention for their potential to reduce environmental risks from nonbiodegradable electronic waste. The present study demonstrates the fabrication of facile, nontoxic, and biodegradable chitosan‐based flexible dielectric substrate using graphene nanoplatelet (GNP) as a nanofiller. The detailed impact of different concentrations of GNP (1, 2, and 3 wt%) into the chitosan (CS) matrix was studied on physicochemical, morphological, mechanical, electrical, and thermal properties. The fabricated CS/GNP composites showed improved mechanical strength, thermal stability, and electrical properties compared with unmodified CS film. The composites exhibited excellent thermal stability (200°C) with a promising biodegradation rate (within 6 days). The mechanical strength of the unmodified CS film was increased unequivocally with 2 wt% GNP loading with tensile strength of 23.56 Mpa. Furthermore, the current–voltage (I–V) characteristic curves for CS/GNP (2%) and CS/GNP (3%) showed similar current conduction and ohmic behavior in flat, bending, and flat‐after‐bending modes. The dielectric measurements revealed that the CS/GNP composite with 2 wt% filler exhibited optimal performance having permittivity (έ) of 32.71 (at 102 Hz) with low dielectric loss of 0.04 (at 106 Hz). These results suggest that the dielectric films offer strong prospects as an eco‐friendly alternative for various applications.Highlights Biodegradable chitosan‐based flexible dielectric films were prepared. Films were made using a simple solvent casting method with 1–3 wt% GNP filler. Optimum physicochemical and electrical properties were seen at 2 wt% GNP. CS/GNP (2%) film exhibited ohmic behavior in both flat and bending modes. Excellent dielectric properties were achieved at 2 wt% GNP filler.

Preparation of highly tunable ZnO/Al2O3-bst50 composite ceramics via defect engineering and composite effect

A series of new x (yZnO/Al2O3)-(1-x)Ba0·5Sr0·5TiO3 (x = 10, 20, 50 wt%, y = 1, 1.3, 1.5 mol) ceramics were prepared by solid-phase method. The effects of ion diffusion and compound effect on the lattice vibration and dielectric properties of Ba0·5Sr0·5TiO3 were studied. When ZnO and Al2O3 are equimolar, the two react to form ZnAl2O4. Under the composite effect, the dielectric permittivity of Ba0·5Sr0·5TiO3 is effectively reduced, Tc moves to high temperature, and the tunability gradually increases. When ZnO is in excess, Tc remains basically unchanged, proving the unique role of the spinel structure. Because ZnO can fully diffuse into Ba0·5Sr0·5TiO3, extremely high tunability is achieved through defect engineering. 50 wt% (ZnO/Al2O3)-50 wt%Ba0·5Sr0·5TiO3 achieved excellent microwave dielectric properties, with dielectric permittivity, tunability and Q value of 201, 23.6 % and 368, respectively. In addition, ZnAl2O4–Ba0.5Sr0·5TiO3 composite ceramics were successfully prepared by directly compounding Ba0·5Sr0·5TiO3 with oxides, which greatly reduced energy loss.

Spectroscopic analysis of defect-induced luminescent and dielectric properties of MgO-based composites on varying dopant concentration

In this novel study, we prepared MgO matrix composites reinforced with varying weight percent ZnO using a solid-state reaction (SSR) method at 500 °C. We aimedto explore the potentialof these composites for high-frequency electronic devices.We conducted a comprehensive structural analysis of these MgO-based composites using various spectroscopic and microscopic techniques. Thisinclusive analysis revealed the morphology, particle size, elemental composition, valence states of elements, and defects in the composites. The Rietveld refinement of XRD data confirmed the presence of binary phase and the phase % of the constituents of composites. XPS spectra demonstrated the isovalent character of Zn/Mg elements and the presence of low-coordinated oxygen ions at the surface of the composites. The UV–visible-based spectroscopic techniques (Absorption and Photoluminescence) further supported the presence of low-coordinated surface O2– ions and F-center defects that caused a significant reduction in the bandgap of the samples. Photoluminescence (PL) analysis suggested the passivation of F-center defects in composites. We also investigated the effect of ZnO concentration and multiple excitation energies on the site-specific localized F-center defects to understand the defect distribution in the composites relative to the host.The dielectric properties of ZnO/MgO composites were assessed through impedance spectroscopy. We observed a significant enhancement in the dielectric constant (∼ 28.69–32.60) of the composites compared to pure MgO (∼12.2) at 1 kHz. This enhancement along with the smaller impedance of the composites relative to the host, as endorsed by the PL results,suggests areduction in F-centers (electrical barriers). This exciting finding paves the way forthe synthesis of ceramic composites with excellent dielectric and optical properties, indicating their potential applications in high-frequency electronic devices.

Relationship between structure and microwave dielectric properties of new low-K garnet-type Ca3Cr2Ge3O12 ceramics

In order to solve the problem of signal delay, a novel low-K Ca3Cr2Ge3O12 ceramic for 5G and millimeter-wave communication was prepared by a solid-state reaction method. XRD and Rietveld refinement results confirm that it belongs to the garnet structure with the Ia-3d space group. The shrinkage rate of the sample sintered at 1350 °C reached 11.9 %, and the relative density exceeded 94.3 %. Excellent microwave dielectric properties were obtained. The permittivity was 8.38, the quality factor was 23,107 GHz, and the temperature coefficient of resonant frequency was −43.57 ppm/°C. The relationship between the crystal structure and microwave dielectric properties of ceramics was further studied. The results show that lattice vibration, stacking fraction and bond strength have a great influence on the Q × f value of ceramics, and the bond valence parameter is the key factor affecting the temperature stability. In addition, the theoretical quality factor of the ceramic can reach ∼13,0000 GHz by far-infrared reflection spectroscopy, and the ceramic has great research potential. The development of Ca3Cr2Ge3O12 ceramics and the study of microwave dielectric properties have filled the research gap of related systems. The excellent microwave dielectric properties indicate that it can be used as an alternative material for the preparation of components in the field of communication.

Comparative Study of Natural Fibres to Improve Insulation in Wooden Beehives Using Sensor Networks

The beekeeping sector is increasingly focused on creating optimal and natural environments for honeybees to reduce dependence on external factors, especially given progressively hotter summers. Improving hive thermal conditions can enhance bee wellbeing and production. While pinewood hives are predominant, some have started using insulating materials like polystyrene. However, many synthetic materials, despite their excellent insulation properties, are incompatible with organic food production, requiring alternative solutions. This study compares the thermal insulation properties of various natural materials, including white and black agglomerated cork, wood fibres, and rock mineral wool. These materials are potentially compatible with organic food production. Additionally, the research evaluates cost-effective sensor networks to monitor bioclimatic variables in real time. Lab tests using a Langstroth-type hive with a controlled heat source were conducted, monitoring temperature and humidity inside and outside the hive. The results revealed that all selected materials provided similar thermal insulation, superior to a hive without insulation. This finding suggests that using natural materials can enhance hive thermal comfort (i.e., the material’s ability to maintain a stable internal temperature), thereby improving honeybee wellbeing and productivity in a manner compatible with organic food production.

The thermal conductivity of graphite composite insulation boards: A theoretical and experimental study

Graphite composite insulation boards (GCIB) have emerged as a promising solution in the construction industry, offering a combination of fire resistance, high temperature stability, and excellent insulation properties. As their usage continues to increase, it is crucial to develop and validate a more accurate theoretical model for the effective design and optimization of building insulation systems. Traditional models including series and parallel models are employed for estimating the thermal conductivity of GCIB but revealed higher relative errors and lower theoretical calculation accuracy. Therefore, the primary objective is to design and validate a more efficient theoretical model for thermal conductivity prediction in GCIB. This paper investigates the thermal conductivity of GCIB under varying composition ratios by designing a novel Parallel-Series Parallel (PSP) approach. The PSP model is designed based on a single basic cell where the graphite polystyrene particles are employed as the matrix material while cement, vitrified microspheres, and silica fume are used as inclusion materials. Then, the thermal conductivity unit is divided into three parallel heat conduction subunits where the matrix materials and inclusion materials in the three subunits are integrated in a series-parallel manner to provide a more realistic representation of the heat transfer mechanisms within the composite. For a comprehensive assessment, the study encompasses theoretical analysis, empirical assessment, and finite element (FE) simulations to illustrate its thermal properties. The predicted thermal conductivity reveals perfect consensus in comparison with the FE and experimental test outcomes by achieving lower relative errors of 2.7 %∼3.8 % and 1.9 %∼ 3.0 % respectively. The model validated through numerical simulations and sample experiments illustrates a significant improvement in accuracy of about 76.4 %∼94.3 % when compared to traditional series and parallel methods. Prominently, the findings indicate that the thermal conductivity of GCIBs declines considerably as the volumetric ratio of graphite polystyrene particles (Ф1/Ф3) increases and stabilizes when the proportion reaches 10, emphasizing the importance of optimizing material composition to enhance the thermal performance of GCIB. Overall, the validated PSP model by accurately determining the thermal conductivity of GCIB serves as a reliable tool for designing and optimizing high-performance insulation materials, contributing to energy efficiency and sustainability in building and construction industries.

Multi-physical field coupling modeling of microwave heating and reduction behavior of zinc oxide

Microwave heating provides a cleaner pyrometallurgical method for separating zinc from electric arc furnace dust (EAFD, a solid waste generated during steel production with excellent dielectric properties). Despite its undisputed heating efficiency, the impact of microwave heating characteristics on the zinc removal process from EAFD remains unclear. This paper focuses on ZnO, one of the primary components of EAFD, and develops an electromagnetic-thermal-chemical reaction model to analyze the effects of microwave power and graphite addition on heating behavior, reduction reactions, field distributions, and reaction kinetics. The results indicate that the heat generated from the interaction between microwaves and materials exhibits inherent non-uniformity, leading to the localized thermal effect and making the error of general temperature measurement methods. Increasing microwave power and adding graphite enhance heating efficiency and promote the reduction reaction but also result in significant internal-external temperature disparity and worse temperature distribution. At 1000 W, with 1.2 times the stoichiometric amount of graphite addition, the temperature measurement error reaches approximately 200 °C, potentially affecting the kinetic results to a certain degree. The non-isothermal kinetics results from simulations indicate that the localized thermal region exhibits a lower average activation energy of 47.5 kJ/mol compared to experimental results, suggesting that the lower activation energy of the ZnO reduction reaction during microwave heating is primarily caused by the localized thermal effect rather than the non-thermal effect. Additionally, in the energy distribution, the higher proportion of return loss during heating underscores the importance of a well-designed microwave heating system.

Polyphenylene oxide/SiO2 composites: Towards ultra-low dielectric loss and high thermal conductivity of microwave substrates

With the rapid development of electronic information industry has raised the requirements for the performance of electronic components. Therefore, it is essential to research dielectric substrate materials with excellent dielectric properties and good thermal conductivity at high frequencies. This study introduced vinyl trimethoxysilane (VTMS) surface-functionalized silicon dioxide (SiO2) into the polyphenylene oxide/styrene–butadiene–styrene/triallyl isocyanurate (PST) composite resin to prepare PST/V-SiO2 composite. The microwave composite substrates for high-speed signal propagation were prepared through a process involving scraping coating and hot pressing. The study investigated the impact of varying amounts of V-SiO2 on the dielectric property, thermal stability, and thermal conductivity of the composites. The microwave composite substrates exhibit excellent dielectric properties and good thermal conductivity. When the V-SiO2 content is 80 wt%, the dielectric loss is 1.8 × 10-3 with a low dielectric constant (≤3.23@10 GHz). Furthermore, the PST/V-SiO2 composite displays higher thermal conductivity (0.735 W/(m·K)) and low moisture absorption. This research provides a novel strategy to develop microwave composite substrates with low dielectric loss and high thermal conductivity.

Realization of ultra-high temperature stability and excellent electrical properties in LTO-based ceramics via A/B-site co-doing

La2Ti2O7 (LTO) ceramics, ideal for ultra-high temperature applications with a Curie temperature near 1460 °C, were previously limited by a low piezoelectric coefficient (d33) of 1.5 pC/N. In this work, the incorporation of Bi3+ and V5+ dopants have been employed to augment the piezoelectric properties of LTO. An enhanced d33 ∼ 4.0 pC/N is achieved in La1.91Bi0.09Ti1.97V0.03O7 (LBTV9) ceramics, while maintaining an ultra-high Curie temperature of 1437 °C. This improvement is attributed to local heterogeneity in the lattice structure induced by the doping. LBTV9 ceramics also exhibit excellent high-temperature stability and insulation properties, maintaining a d33 at 4.0 pC/N after annealing at 1000 °C for 48 h and stabilizing at 4.2 pC/N across temperatures from 200 °C to 1600 °C, with a DC resistivity of 1.7 × 106 Ω·cm at 1000 °C. These enhancements make LBTV9 ceramics suitable for extreme condition applications, thus unlocking new possibilities for their use in ultra-high temperature piezoelectric devices.

High-temperature relaxation and microwave dielectric response of (1-x)BaNd1.76Bi0.24Ti5O14-xBa0.6Sr0.4La4Ti4O15 compounds with adjustable medium-high dielectric constant

Dielectric ceramics in the microwave band are one of the crucial materials for mobile communication technology, and the studying of their phase evolution and defect behavior can help to understand and reduce dielectric loss. In this work, (1-x)BaNd1.76Bi0.24Ti5O14-xBa0.6Sr0.4La4Ti4O15 (x = 0.2, 0.4, 0.6 and 0.8, (1-x)BNT-xBSLT) ceramics were synthesized by solid-state reaction method. X-ray diffraction (XRD) and Raman spectra analysis reveal that tungsten bronze and hexagonal perovskite phases coexist in the ceramics, and BaNd2Ti3O10 is indexed as the main crystalline phase at x = 0.4, 0.6, leading to a deterioration of the microwave dielectric properties. The defect-related relaxation behavior and its effect on microwave dielectric properties were analyzed by dielectric temperature spectrum and thermally stimulated depolarization current (TSDC). The relationship between the dielectric constant and the electric field distribution was solved using the eigenmode of the high frequency structure simulator. In short, the (1-x)BNT-xBSLT ceramics at x = 0.8 exhibit excellent microwave dielectric properties: εr = 47.2, Q×f = 16,800 GHz, and τf = −4.6 ppm/°C. The microwave dielectric response of BNT-BSLT composite ceramics is closely related to the phase composition and defects, which is informative for the development of low dielectric loss ceramics.

Understanding of the correlation of structural and microwave dielectric performance of (1-x)MgTiO3 - xCaTiO3 ceramics for dielectric resonator antenna applications

In this article, the effect of CaTiO3 on the structural and microwave dielectric characteristics of MgTiO3 has been discussed. The (1-x)MgTiO3 - xCaTiO3 (abbreviated as (1-x)MT- xCT) for x = 0.025, 0.05, 0.075, 0.1 ceramics have been developed using a solid-state reaction route. The structural as well as morphological characteristics of specimens have been observed by employing X-ray diffraction and scanning electron microscope methods. The Rietveld refinement technique of X-ray diffraction data have been conducted for the refinement of structural phases. It suggests that two crystallographic phases have been present in all materials. The SEM images display dense well-identified grains of (1-x)MT - xCT (for x = 0.025 - 0.1) ceramics. The Raman spectroscopy method has been employed to detect the symmetry of ceramics and modes of vibration of the materials. The microwave dielectric characteristics like dielectric permittivity (εr), loss (tanδ), quality factor (Q×f), and temperature coefficient at resonant frequency (τf) of (1-x)MT - xCT (for x = 0.025 - 0.1) ceramics have been thoroughly investigated. The bond strength, bond valency, bond energy, and tolerance factor of (1-x)MT - xCT (for x = 0.025 - 0.1) materials have been evaluated and their relation with microwave dielectric characteristics has been discussed. The (1-x)MT - xCT (for x = 0.025 - 0.1) ceramics show excellent dielectric properties with near to zero τf. In addition, DRAs have been designed with (1-x)MT - xCT (for x = 0.025 - 0.1) materials as dielectric resonators and various antenna properties have been studied with the help of HFSS software. This work suggests that (1-x)MT - xCT for (x=0.05) material can be a promising candidate for DRA applications working in the C band.

Ultra-small size and crystal-axis-oriented BaTiO3 nanocrystals: Dielectric and photocatalytic response

With the development of modern nanotechnology, the application range of BaTiO3 (BT) materials has been expanded, and the design and synthesis of micro-nano scale BT materials have become one of the hot spots. In this study, ultra-small BaTiO3 (Ultra-BT) were prepared by solvothermal-calcination reaction. First, the BT precursor was prepared by solvothermal reaction with ethylene glycol as solvent, and then the BT precursor was calcined to obtain Ultra-BT. The Ultra-BT at this time is composed of uniform [010]-crystal-axis-oriented BT nanocrystals with a size of about 28 nm. The formation mechanism of Ultra-BT was revealed, namely the dissolution-deposition reaction. Ultra-BT are more favorable for the preparation of BT ceramics with uniform grain because of their ultra-small size. At a sintering temperature of 1220 °C, the dielectric constant of BT ceramics at the Curie temperature is 8661. This dielectric constant value is higher than that reported for BT ceramics in most literature, and even higher than some doped modified BT ceramics. The solvothermal-calcination method used for preparing Ultra-BT provides important reference value for the preparation of other ultra-small perovskite materials. At the same time, because of the excellent dielectric properties and good catalytic properties of Ultra-BT, it has potential application value in the field of dielectric and catalysis.

Efficient gradient heating-up approach for rapid growth of high-quality amorphous ZrO2 dielectric films

High-k oxide dielectric films are indispensable for low-power-consumption oxide thin-film transistors (TFTs) applied in advanced and portable electronics. However, high-quality oxide dielectric films prepared by solution process typically require sophisticated processes and long thermal annealing time, severely limiting both the throughput manufacturing and cost-effectiveness. In this study, the influence of different heating-up methods on the surface morphology and dielectric properties was systematically investigated. Gradient heating-up method could not only substantially improve the surface morphology and quality of high-k ZrO2 films but also efficiently shorten the annealing time. The gradient heating-up process was further designed on the basis of thermal behavior of the xerogel-like precursor, which successfully realize the preparation of high-quality ZrO2 films with an annealing time of 5 min (i.e. the efficiency of thermal treatment increased by about 89%). The ZrO2 film presented excellent dielectric properties, including a low leakage current density of ∼10−8 A cm−2 (at 2 MV cm−1 ), a large areal capacitance of 169 nF cm−2 and a high dielectric constant of 20.41 (1 MHz). Furthermore, InSnZnO TFT based on the ZrO2 gate dielectrics shows an acceptable device performances, such as a high carrier mobility of 2.82 cm2 V−1 s, a high on/off current ratio of ∼105 and a low subthreshold swing of 0.19 V decade −1 at a low operation voltage of 5 V. This work provide a highly promising approach to fabricate high-quality solution-processed high-k oxide dielectric films employed for large-scale and low-power-consumption electronics.

Polyetherimide nanocomposite with enhanced mechanical, thermal and dielectric properties by incorporating synergistically exfoliated‐chemical functionalization induced hexagonal boron nitride nanosheets

AbstractThe present study aims to improve the mechanical, thermal and dielectric properties of polyetherimide (PEI) nanocomposite via simplified method, involving the creation of a nanocomposite using PEI incorporated with exfoliated‐chemical functionalization induced hexagonal boron nitride nanosheets (BNNS). XRD, FTIR and Raman elucidated the chemical structure of functionalized BNNS and indicated the success preparation of functionalized BNNS. Functionalization effectively improved the compatibility of nanocomposites and contributed to the property improvements. Morphological analysis unveiled a compact and dense microstructure within the nanocomposites in correlation with functionalized BNNS. Broad band dielectric spectroscopy revealed excellent dielectric properties of produced PEI nanocomposite. DMA testing verified a noteworthy enhancement in both Tg and storage modulus upon incorporating of BNNS. In summary, this comprehensive investigation highlights the impact of functionalized BNNS on mechanical, thermal and dielectric properties of developed PEI dielectric nanocomposite and is expected to expand the application of PEI in the field of high‐temperature energy storage.Highlights Polyetherimide (PEI) was used as polymer matrix and boron nitride derivatives as dielectric fillers to prepare PEI dielectric nanocomposite. Due to the influences of dielectric properties by interface polarization effect and the local distribution of electric field of the fillers in PEI matrix, the dielectric constant, breakdown strength and energy storage density of PEI nanocomposites were obviously improved compared with pure PEI. The effects of interfacial interactions between PBNNS and PEI contributes to the uniform dispersion and comprehensive property improvements of PEI dielectric nanocomposites. This work presents a systematic investigation into the fabrication of PEI/BNNS nanocomposite using a one‐step solution blending method, inspiring the research and development of PEI in the energy storage applications areas in the future.

The effect of different active diluents on the properties of epoxy materials

Abstract Epoxy resin is widely used in the insulation packaging field of electrical equipment due to its advantages such as low cost, excellent insulation, and mechanical properties. However, the thermal conductivity and the heat resistance of domestic epoxy insulation packaging materials make it difficult to meet the increasingly demanding operating conditions of electrical equipment. This article investigated the effects of active diluents with different functional group numbers on the glass transition temperature, mechanical strength, and low-temperature cracking resistance of epoxy materials. Four functional group active diluents were selected as additives to reduce the viscosity of epoxy resin, and the influence of diluent content on the comprehensive performance of epoxy resin was studied and analyzed.

Lightweight and robust electrospun zirconia fiber reinforced carbon aerogel composites for efficient microwave absorption and heat insulation

Carbon aerogel (CA) is recognized as a promising microwave absorption (MA) material, but it remains greatly challenging to integrate the multiple functions of MA, mechanical strength, and heat insulation. In this work, a novel zirconia fiber reinforced CA (ZF/CA) composite is successfully fabricated via electrospinning technology coupled with a sol-gel impregnation process for the first time. The density (0.132–0.206 g/cm3) of the obtained ZF/CA composites can be regulated by simply varying the initial sol concentration, thus effectively tuning their performance. Notably, the ZF/CA composites display excellent MA properties, with a strong absorption of −80.30 dB at the thickness of merely 1.71 mm and the optimal effective absorption bandwidth reaches 5.16 GHz, which is a significant improvement compared to CA (−11.70 dB, 0.58 GHz). Simultaneously, the brittleness and cracking problems of CA are effectively addressed by the soft reinforcement strategy of electrospun zirconia fibers, and superior mechanical strength is obtained. Furthermore, the nanopore structure and hierarchical design endow the ZF/CA composites with low thermal conductivity (0.029–0.038 W m−1 K−1) and favorable heat insulation performance. Outstanding MA capacity and excellent heat insulation properties along with lightweight construction and high strength make ZF/CA composites a great candidate for efficient MA and heat insulation.

Photocurable comb polyamic acid for solvent-free direct ink writing with low dimensional shrinkage

Polyimides are high-performance organic polymers with excellent insulation, high-temperature resistance, and mechanical properties. However, their poor solubility makes it challenging to use them to prepare solvent-free high-performance photocurable polyimide inks with low dimensional shrinkage. In this study, photocurable comb polyamic acid resins were synthesized, and their solubility was examined based on density functional theory (DFT) calculations. Experiments showed that polyamic acid resins with specific topologies could be dissolved in photocurable monomers to prepare solvent-free photocured polyimide inks. A custom-made UV-assisted direct ink writing 3D printer was used to fabricate complex three-dimensional devices. Further heat treatment caused the polyamic acids to undergo dehydration and cyclization into rigid polyimide structures, and this process exhibited less than 6% dimensional shrinkage. The final material had a maximum storage modulus of 3.1 GPa (40 ℃) and a glass transition temperature of 204 ℃. The good comprehensive performance suggests great potential for aerospace applications.