Biomimetic Nacreous Composite Films toward Multipurpose Application Structured by Aramid Nanofibers and Edge-Hydroxylated Boron Nitride Nanosheets

Novel production of basalt nanosheets with ultrahigh aspect ratios and their assembly with nylon membranes for high-performance electrical insulating composite membranes

The rapid advancement of modern electrical equipment has significantly increased the demand for advanced electrical insulating materials. Traditional silicate nanosheets are widely used as fillers in electrical insulating composites. However, their low aspect ratio restricts their effectiveness in high-performance electrical insulating applications. Here, a three-step liquid exfoliation strategy is proposed to prepare basalt nanosheets (BSNs) with an ultrahigh aspect ratio (up to 1397) from basalt scales (BS). This process involves cation exchange on BS to generate lamellar structures, serving as the basis for the preparation of lithium ion-exchanged BSNs (LBSNs). Next, oxalic acid/hydrogen peroxide treatment breaks the chemical bonds within the LBS sediment, producing chemically treated BSNs (CBSNs). Finally, BSNs are prepared by mixing LBSNs and CBSNs, followed by differential centrifugation to isolate BSNs with an ultrahigh aspect ratio (BSNs-1000). Subsequently, inspired by the overlapping structure of pangolin skin, BSNs-1000 are assembled onto nylon membranes, forming biomimetic nylon/BSNs-1000 (N/B-1000) composite membranes with an overlapping surface structure. This structure forms an effective physical barrier, impeding charge and crack propagation, thereby significantly enhancing their electrical insulating and mechanical properties. The novel exfoliation method and biomimetic strategy provide effective approaches for developing advanced electrical insulating membranes for high-performance electrical equipment.

Poly(vinyl alcohol)-Assisted Exfoliation and Grafting Modification of Boron Nitride Nanosheets with a High Aspect Ratio via a Continuous Production Method for Energy Storage and Thermal Management

Hexagonal boron nitride nanosheets (BNNS) integrating many extraordinary properties are usually combined with polymers to fabricate multifunctional dielectric materials for energy storage and thermal management. Unfortunately, the existing technologies for producing BNNS generally have the disadvantages of inefficiency and low product quality, which significantly hinder the wide application of high-value nanocomposites. Herein, a novel poly(vinyl alcohol) (PVA)-assisted pan-milling method based on the innovative solid-state shear milling (S3 M) technology is reported for the production of high-quality BNNS. The uniform three-dimensional (3D) shear force field generated by pan milling not only ensured the high aspect ratio of BNNS (the average lateral size of ∼954 nm and the average thickness of ∼3.7 nm) but also induced the mechanochemical reaction between PVA and BNNS to achieve in situ grafting modification on the BNNS surface. The simultaneous high-quality exfoliation and surface modification of BNNS positively contributed to the mechanical, dielectric, and thermal conduction properties of BNNS/PVA nanocomposites. At the BNNS content of 10 wt %, the BNNS/PVA composite film exhibited excellent robustness (Young's modulus of 5305 MPa and the tensile strength of 83 MPa), with a satisfactory breakdown strength (Eb of 134.7 MV/m) and dielectric constant (∼5 at 1000 Hz). In addition, the substantial improvement of thermal conductivity (from 0.88 to 5.59 W·m-1·K-1) guaranteed the stability of the dielectric properties of the nanocomposites at high temperatures. This pan-milling method characterized by green and efficiency is highly scalable to other two-dimensional (2D) layered materials, providing a practical strategy for the industrial fabrication of nanocomposites in elevated-temperature energy storage.

Anisotropic Heat Transfer in a Fibrous Membrane with Hierarchically Assembled 2D Materials

Effective heat redistribution in specific directions is vital for advanced thermal management, significantly enhancing device performance by optimizing spatial heat configurations. We have designed and fabricated a hierarchical fibrous membrane that enables precise heat directing. By integrating hierarchical structure design with the anisotropic thermal conductivity of two-dimensional (2D) materials, we developed a fibrous membrane for anisotropic heat transfer. Such a structure is fabricated by aligning a 1D structured fiber in the 2D plane to achieve anisotropy at each scale level. The fiber units, where 2D nanosheets circumferentially and axially aligned, achieved a high axial thermal conductivity of 16.8 W·m-1·K-1 and advanced heat directing ability, confirmed by characterizations and simulations. The assembled membrane demonstrated an exceptional tensile strength (365 MPa) and high thermal conductivity (10.5 W·m-1·K-1) along the fiber axis. Our membranes are seen as a refined model for thermal management materials, combining the benefits of heat spreaders and thermal interface materials, thus being proficient in directing heat along programmed pathways. A practical wireless charging cooling demonstration illustrated this. Our methodology also proved versatile with different 2D fillers and various geometries. This research presents a method to achieve precise heat directing at the material's level, facilitating the systematic design of thermal management in electronics.

Enhanced mechanical and dielectric properties of lignocellulosic composite papers with biomimetic multilayered structure and multiple hydrogen-bonding interactions

Lignocellulosic papers (LCP) are favored for electrical insulating applications due to their environmental friendliness, ease of processing, and cost-effectiveness. However, the loose structure and numerous pores inside LCP result in the poor mechanical and electrical insulating properties, posing challenges in meeting the requirements for the rapid upgrading of high-voltage electrical equipment. Herein, a 3D interconnective structure composed of 3D aramid nanofibers (ANF) and 2D carbonylated basalt nanosheets (CBSNs) is introduced to enhance the structure and the chemical bonding interactions of LCP. This is achieved by impregnating LCP into an ANF-CBSNs suspension, where the 3D interconnective ANF framework hosts numerous CBSNs. The resultant LCP/ANF-CBSNs (LCP/A-C) composite papers exhibit multilayered structure and multiple hydrogen-bonding interactions, demonstrating excellent mechanical and electrical insulating properties. Notably, the optimized LCP/A-C5 composite papers exhibit remarkable tensile strength (23.15 MPa) and dielectric breakdown strength (20.14 kV·mm-1), respectively, representing 229 % and 145 % increase compared to those of the control LCP. These impressive properties are integrated with excellent bending ability, outstanding high temperature resistance, exceptional volume resistivity, and low dielectric constant and loss, demonstrating their potential as highly promising electrical insulating papers for advanced high-power electrical equipment.

Significantly Improve the Thermal Conductivity and Dielectric Performance of Epoxy Composite by Introducing Boron Nitride and POSS

Dielectric materials with superb thermal and electrical properties are highly desired for high-voltage electrical equipment and advanced electronics. Here, we propose a novel strategy to improve the performance of epoxy composites by employing boron nitride nanosheets (BNNSs) and γ-glycidyl ether oxypropyl sesimoxane (G-POSS) as functional fillers. The resultant ternary epoxy composites exhibit high electrical resistivity (1.63 × 1013 Ω·cm) and low dielectric loss (<0.01) due to the ultra-low dielectric constants of cage-structure of G-POSS. In addition, a high thermal conductivity of 0.3969 W·m-1·K-1 is achieved for the epoxy composites, which is 114.66% higher than that of pure epoxy resin. This can be attributed to the high aspect ratio and excellent thermally conductive characteristics of BNNSs, promoting phonon propagation in the composites. Moreover, the epoxy composite simultaneously possesses remarkable dynamic mechanical properties and thermal stability. It is believed that this work provides a universal strategy for designing and fabricating multifunctional composites using a combination of different functional fillers.

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.