Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Resistance change under mechanical stimuli arouses mass operational heat, damaging the performance, lifetime, and reliability of stretchable electronic devices, therefore rapid thermal heat dissipating is necessary. Here we report a stretchable strain sensor with outstanding thermal management. Besides a high stretchability and sensitivity testified by human motion monitoring, as well as long-term durability, an enhanced thermal conductivity from the casted thermoplastic polyurethane-boron nitride nanosheets layer helps rapid heat transmission to the environments, while the porous electrospun fibrous thermoplastic polyurethane membrane leads to thermal insulation. A 32% drop of the real time saturated temperature is achieved. For the first time we in-situ investigated the dynamic operational temperature fluctuation of stretchable electronics under repeating stretching-releasing processes. Finally, cytotoxicity test confirms that the nanofillers are tightly restricted in the nanocomposites, making it harmless to human health. All the results prove it an excellent candidate for the next-generation of wearable devices. Though stretchable strain sensors are attractive for next-generation applications due to their high sensitivity, heat generated in these devices limits their reliability. Here, the authors report boron nitride nanosheet-based stretchable strain sensors with enhanced thermal management.

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A high performance wearable strain sensor with advanced thermal management for motion monitoring.

Author(s): Ai, Ding; Li, He; Zhou, Yao; Ren, Lulu; Han, Zhubing; Yao, Bin; Zhou, Wei; Zhao, Ling; Xu, Jianmei; Wang, Qing

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Tuning Nanofillers in In Situ Prepared Polyimide Nanocomposites for High-Temperature Capacitive Energy Storage

Polymers are the preferred materials for dielectrics in high-energy-density capacitors. The electrification of transport and growing demand for advanced electronics require polymer dielectrics capable of operating efficiently at high temperatures. In this review, we critically analyze the most recent development in the dielectric polymers for high-temperature capacitive energy storage applications. While general design considerations are discussed, emphasis is placed on the elucidation of the structural dependence of the high-field dielectric and electrical properties and the capacitive performance, including discharged energy density, charge-discharge efficiency and cyclability, of dielectric polymers at high temperatures. Advantages and limitations of current approaches to high-temperature dielectric polymers are summarized. Challenges along with future research opportunities are highlighted at the end of this article.

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Dielectric polymers for high-temperature capacitive energy storage.

Abstract In contrast to the comprehensive understanding of novel ferroelectric [i.e., relaxor ferroelectric (RFE) and antiferroelectric] behavior in ceramics, RFE and double-hysteresis-loop (DHL) behavior in crystalline ferroelectric polymers have only been studied in the past fifteen years. A number of applications such as electrostriction, electric energy storage, and electrocaloric cooling have been realized by utilizing these novel ferroelectric properties. Nonetheless, fundamental understanding behind these novel ferroelectric behaviors is still missing for polymers. In this feature article, we intend to unravel the basic physics via systematic studies of poly(vinylidene fluoride- co -trifluoroethylene) [P(VDF-TrFE)]-based terpolymers, electron-beam (e-beam) irradiated P(VDF-TrFE) copolymers, and PVDF graft copolymers. It is found that both the crystal internal structure and the crystal–amorphous interaction are important for achieving the RFE and DHL behaviors. For the crystal internal structure effect, dipole switching with reduced friction and nanodomain formation by pinning the polymer chains are essential, and they can be achieved through crystal repeating-unit isomorphism (i.e., defect modification). Physical pinning [e.g., in P(VDF-TrFE)-based terpolymers] induces a reversible, electric field-induced RFE↔FE phase transition and thus the DHL behavior, whereas chemical pinning [e.g., in e-beam irradiated P(VDF-TrFE)] results in the RFE behavior. Finally, the crystal–amorphous interaction (or the nanoconfinement effect) results in a competition between the polarization and depolarization local fields. When the depolarization field becomes stronger than the polarization field, a DHL behavior is observed. Obviously, the physics for ferroelectric polymers is different from that for ceramics/liquid crystals and can be largely attributed to the long-chain nature of semicrystalline polymers. This understanding will help us to design new ferroelectric polymers with improved properties and/or better applications.

Novel Polymer Ferroelectric Behavior via Crystal Isomorphism and Nanoconfinement Effect

https://onlinelibrary.wiley.com/doi/epdf/10.1002/aenm.201903062

High Energy Density Polymer Dielectrics Interlayered by Assembled Boron Nitride Nanosheets

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems. Although incorporating insulating, inorganic nanostructures into dielectric polymers promotes the temperature capability, scalable fabrication of high-quality nanocomposite films remains a formidable challenge. Here, we report an all-organic composite comprising dielectric polymers blended with high-electron-affinity molecular semiconductors that exhibits concurrent high energy density (3.0 J cm−3) and high discharge efficiency (90%) up to 200 °C, far outperforming the existing dielectric polymers and polymer nanocomposites. We demonstrate that molecular semiconductors immobilize free electrons via strong electrostatic attraction and impede electric charge injection and transport in dielectric polymers, which leads to the substantial performance improvements. The all-organic composites can be fabricated into large-area and high-quality films with uniform dielectric and capacitive performance, which is crucially important for their successful commercialization and practical application in high-temperature electronics and energy storage devices. Dielectric polymers are widely used in electrostatic energy storage but suffer from low energy density and efficiency at elevated temperatures. Here, the authors show that all-organic composites containing high-electron-affinity molecular semiconductors exhibit excellent capacitive performance at 200 °C.

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Polymer/molecular semiconductor all-organic composites for high-temperature dielectric energy storage.

Interface-modulated nanocomposites based on polypropylene for high-temperature energy storage

Charge cluster triggers unpredictable insulation surface flashover in pressurized SF 6

Polymer nanocomposites incorporated with high-dielectric-constant nanoparticles are widely studied as the dielectric materials for high-energy-density electrostatic capacitors. However, the associated concerns of the embedded nanoparticles such as local electric field distortion and high leakage current limit the substantial improvement of energy density. In this work, a novel design of hierarchically-structured nanofillers is demonstrated, which show remarkable advantages over conventional high-dielectric-constant nanoparticles for polymer nanocomposites. These hierarchical nanostructures are prepared by covalently tethering the barium titanate (BT) nanoparticles on the basal plane of the two-dimensional boron nitride nanosheets. The grafting density of BT in the hierarchical nanostructures is adjustable such that its dielectric properties can be tuned, and the capacitive energy storage performance of the nanocomposites can be optimized. Both the experimental results and computational simulations prove that the hierarchically-structured nanofillers can effectively suppress the local field distortion and reduce leakage current. The resulting polymer nanocomposite exhibits a high discharged energy density which is 137% greater than that of a conventional nanocomposite with the same content of freely dispersed BT nanoparticles, in addition to a much improved charge–discharge efficiency. The proposed hierarchically-structured nanofillers shed light on the design of polymer nanocomposites with high energy density and high charge–discharge efficiency.

Yujie Zhu

Papers

High Energy Density Polymer Dielectrics Interlayered by Assembled Boron Nitride Nanosheets

Polymer/molecular semiconductor all-organic composites for high-temperature dielectric energy storage.

Interface-modulated nanocomposites based on polypropylene for high-temperature energy storage

Charge cluster triggers unpredictable insulation surface flashover in pressurized SF 6

Polymer nanocomposites with high energy density and improved charge–discharge efficiency utilizing hierarchically-structured nanofillers