Mussel-Inspired and Magnetic Co-functionalization of Hexagonal Boron Nitride in Poly(vinylidene fluoride) Composites Toward Enhanced Thermal and Mechanical Performance for Heat Exchangers

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.

Mechanically robust, transparent, and UV-shielding composite of Na-Alginate and maleic acid-functionalized boron nitride nanosheets with improved antioxidant property

Maleic acid functionalized boron nitride nanosheets (BNNS-MA)/Na-Alginate composite with enhanced mechanical, UV-shielding and antioxidation properties have been fabricated for the first time by solvent evaporation from a homogeneous aqueous dispersion of BNNS-MA/Na-Alginate composite solution. The composite fabrication was driven by homogenous nano-integrations and chemistry of compatibilization of BNNS-MA with Na-Alginate through H-bonding interactions between -COOH functional group of BNNS-MA and -OH, -COONa groups of Na-Alginate. The BNNS-MA/Na-Alginate composites show significant enhancement of mechanical, UV-blocking and antioxidant properties compared to the Na-Alginate. Integrating only 1 wt% BNNS-MA improved the UV-blocking, tensile strength, and antioxidant properties of Na-Alginate film by 99.1%, 73% and 60.3%, respectively. Overall, our findings of BNNS-MA integrated Na-Alginate composite films with improved physical, mechanical, UV shielding, and antioxidant functionalities is very promising to open new insight in the field of transparent UV-protected biopolymer film for consumer products, packaging, cosmetics, and engineering applications.

Achieving High Thermal Conductivity and Satisfactory Insulating Properties of Elastomer Composites by Self-Assembling BN@GO Hybrids

With increasing heat accumulation in advanced modern electronic devices, dielectric materials with high thermal conductivity (λ) and excellent electrical insulation have attracted extensive attention in recent years. Inspired by mussel, hexagonal boron nitride (hBN) and graphene oxide (GO) are assembled to construct mhBN@GO hybrids with the assistance of poly(catechol-polyamine). Then, mhBN@GO hybrids are dispersed in carboxy nitrile rubber (XNBR) latex via emulsion coprecipitation to form elastomer composites with a high λ and satisfactory insulating properties. Thanks to the uniform dispersion of mhBN@GO hybrids, the continuous heat conduction pathways exert a significant effect on enhancing the λ and decreasing the interface thermal resistance of XNBR composites. In particular, the λ value of 30 vol% mhBN@GO/XNBR composite reaches 0.4348 W/(m·K), which is 2.7 times that of the neat XNBR (0.1623 W/(m·K)). Meanwhile, the insulating hBN platelets hinder the electron transfer between adjacent GO sheets, leading to satisfactory electrical insulation in XNBR composites, whose AC conductivity is as low as 10^-10 S/cm below 100 Hz. This strategy opens up new prospects in the assembly of ceramic and carbonaceous fillers to prepare dielectric elastomer composites with high λ and satisfactory electrical insulation, making them promising for modern electrical systems.

Heat Conduction and Antibacterial Hexagonal Boron Nitride/Polypropylene Nanocomposite Fibrous Membranes for Face Masks with Long-Time Wearing Performance

Wearing surgical masks is one of the best protective measures to protect humans from viral invasion during the 2019 coronavirus (COVID-19) outbreak. However, wearing surgical masks for extended periods will cause uncomfortable sweltering sense to users and are easy to breed bacteria. Here, we reported a novel fibrous membrane with outstanding comfortability and antibacterial activity prepared by PP ultrafine fiber nonwovens and antibacterial functionalized h-BN nanoparticles (QAC/h-BN). The thermal conductivity of commercial PP nonwovens was only 0.13 W m^-1 K^-1, but that of the QAC/h-BN/PP nanocomposite fibrous membranes can reach 0.88 W m^-1 K^-1, an enhancement of 706.5% than commercial PP nonwovens. The surface temperature of commercial PP surgical masks was 31.8 °C when the wearing time was 60 min. In contrast, QAC/h-BN/PP surgical masks can reach 33.6 °C at the same tested time, exhibiting stronger heat dissipation than commercial PP surgical masks. Besides, the antibacterial rates of QAC/h-BN/PP nanocomposite fibrous membranes were 99.3% for E. coli and 96.1% for S. aureus, and their antibacterial mechanism was based on "contact killing" without the release of unfavorable biocides. We think that the QAC/h-BN/PP nanocomposite fibrous membranes could provide better protection to people.

Preparation of boron nitride nanosheets via polyethyleneimine assisted sand milling: towards thermal conductivity and insulation applications

The PEI-grafted boron nitride nanosheets were successfully prepared via sand-milling process, which were doped into thermoplastic polyurethane matrix for better in-plane thermal conductivity while maintaining insulation properties.

Millefeuille-Inspired Thermally Conductive Polymer Nanocomposites with Overlapping BN Nanosheets for Thermal Management Applications

Increasing power density makes modern electronic devices and power equipment generate excess heat, which greatly restricts the applications of polymeric materials because of their poor thermal conductivity. In the present work, inspired by the structure and production process of millefeuille cakes, we show that electrostatic spraying of boron nitride nanosheets (BNNSs) onto electrospun poly(vinyl alcohol) (PVA) nanofibers can produce highly thermally conductive, electrically insulating, flexible, and lightweight nanocomposites via a scalable method of building a multilayer PVA/BNNS nanonetwork structure. The PVA/BNNS nanocomposites exhibit an ultrahigh in-plane thermal conductivity of 21.4 W/(m·K) at 22.2 vol % BNNS addition, realized by an orientated BNNS network structure with overlapping interconnections. The BNNS networks exhibit low thermal resistance and interfacial heat scattering between BNNSs. Moreover, for heat dissipation applications, the nanocomposites with an overlapping BNNS network show higher efficiency in dissipating hot spots than randomly dispersed BNNS or directly hot-pressed BNNS composites. These PVA/BNNS nanocomposites can be used as high-performance lateral heat spreaders in next-generation thermal management systems.

Baroplastics with Robust Mechanical Properties and Reserved Processability through Hydrogen-Bonded Interactions

Conventional polymers are usually processed at a much higher temperature than room temperature, which inevitably leads to huge energy consumption and degradation of the polymers and thus a low recycling ability. Herein, we synthesized a poly( n-butyl acrylate)@polystyrene (PBA@PS) core-shell polymer to prepare a typical baroplastic (processible at room temperature). However, this type of baroplastics always has a low mechanical property. To solve this problem, in this work, we introduced hydrogen bonds into the matrix and successfully reinforced baroplastics for the first time. The hydrogen-bonded interaction was introduced by complexing PBA@PS with poly(acrylic acid) and poly(ethylene oxide). The results show that the reinforced baroplastics possessed notably enhanced mechanical properties and good processability. Their mechanical strength and modulus reached as high as 5.6 (by 73%) and 10 MPa (by 400%), respectively. Moreover, the baroplastics could be remolded many times at room temperature and, at the same time, still showed a higher tensile strength (10.5 MPa, 3.3 times that of the initial PBA@PS, which was never achieved in previous works), which resulted from the reversible hydrogen bonds and reserved orientation of molecular chains. Our work opened a new path to reinforce baroplastics and could widen their applications. Furthermore, not limited to the hydrogen bonds, more sacrificial bonds, such as ionic bonds, host-guest interactions, and metal-ligand coordination bonds, could be used to fabricate high-performance baroplastics.

Highly Thermally Conductive Yet Electrically Insulating Polymer/Boron Nitride Nanosheets Nanocomposite Films for Improved Thermal Management Capability

Thermally conductive yet electrically insulating polymer composites are urgently required for thermal management applications of modern electrical systems and electronic devices because of their multifunctionality and ease of processing. However, the thermal conductivity enhancement of polymer composites is usually at the price of the loss of lightweight, the deterioration of flexibility, and electrical insulation. Here we report advanced polymer nanocomposites containing orientated boron nitride nanosheets (BNNSs), which simultaneously exhibit high thermal conductivity enhancement, excellent electrical insulation, and outstanding flexibility. These nanocomposite films can be easily constructed by electrospinning polymer/BNNSs nanocomposite fibers, vertically folding the electrospun nanocomposite fibers and the subsequent pressing. The nanocomposite films exhibit thickness-dependent in-plane thermal conductivity, which can reach 16.3 W/(m·K) in the 18 μm thick nanocomposite film with 33 wt % BNNSs. In addition, the nanocomposite films have superior electrically insulating properties compared with the pristine polymer, such as reduced dielectric loss, increased electrical resistivity, and enhanced breakdown strength. The strong thermal management capability of the nanocomposite film was demonstrated in switching power supply, which showed the importance of high in-plane thermal conductivity in thermal management of high-power density electronic devices.