Fiber Reinforced Layered Dielectric Nanocomposite

Abstract

Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self-assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum-assisted layerby-layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofibernanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4-20-fold increase of stiffness), light weight (density ≈1.01 g cm −3 ), dielectric stability over a broad range of temperature (25-200 °C) and frequencies (10 3 -10 6 Hz), good dielectric breakdown strength (≈292 MV m −1 ), and excellent thermal management capability (about 5-24 times higher thermal conductivity) such as fast heat dissipation.

Highly Thermally Conductive Dielectric Nanocomposites with Synergistic Alignments of Graphene and Boron Nitride Nanosheets

“…Remarkably, however, the current rGO‐PI/BNNS‐PI composite exhibited both a high thermal conductivity and a high dielectric constant to loss ratio at the same low total filler loading of 2.5 vol% (at an rGO to BNNS weight ratio of 1). By contrast, high filler contents of over 7 vol% were required for the BNNS/polymer composites [ 1,10 ] (green symbols in Figure 6c) to achieve similar dielectric constant to loss ratios (Table S3, Supporting Information). The combination of a high thermal conductivity of our nanocomposites together with the high T g of PI matrix [ 7 ] could further extent the application of dielectric composites to high‐temperature regime.…”

“…[ 4 ] In addition, recent advances in miniaturization and integration of electronics, such as embedded capacitors in electronics packaging and energy storage capacitors in electric vehicles, call for multifunctional polymer dielectrics possessing both high energy densities and excellent thermal management capabilities to effectively dissipate the heat generated during charge–discharge cycles in order to ensure the reliability and service life of electronics. [ 1,4 ] While many engineering polymers with high glass transition temperatures ( T g ), such as polyimide (PI), [ 6,7 ] polyethylenimine (PEI), [ 8 ] crosslinked benzocyclobutene (c‐BCB), [ 1,9 ] and polyaramid nanofibers, [ 10 ] have been used to improve the thermal stability, they have low thermal conductivities ranging 0.1–0.5 W m −1 K −1 and thus highly prone to thermal breakdown induced by the local heat generated by energy losses during charge–discharge cycles. Therefore, it is critical to develop multifunctional high‐ k polymer dielectrics with simultaneous low loss and outstanding thermal conductivities.…”

“…On the other hand, 2D h‐BN is an electrical insulator with an intrinsic wide bandgap of ≈5.5 eV and a high breakdown strength of ≈800 MV m −1 . [ 24,25 ] The addition of BN nanosheets (BNNS) made by solution‐based exfoliation [ 1,10 ] or chemical vapor deposition [ 8,26 ] into dielectric polymers mitigated their dielectric losses to as low as 0.01, giving rise to high breakdown strengths. Yet the dielectric constants of BNNS/polymer composites were mostly mediocre (<10) because of the inherently low dielectric constant of BNNS.…”

Fabrication, Applications, and Prospects of Aramid Nanofiber

“…In addition, thermally conductive but electrically insulating polymer composites are highly desirable for thermal management applications. [ 100 ] Therefore, Rahman et al [ 101 ] proposed a self‐assembled nanocomposite insulation paper through a vacuum‐assisted LBL infiltration process, as shown in Figure 17D. In the insulation nanocomposite paper, 2D boron nitride nanosheets provide thermally conductive networks while the 1D ANF provides appropriate mechanical properties through entangled nanofiber–nanosheet morphologies.…”

“…The ANF‐BNNS nanocomposite insulation paper exhibited a 5–24 times higher thermal conductivity than that of the conventional insulation polymer. [ 101 ] This highly thermal conductive insulation composite paper would solve the issue of heat dissipation and significantly ensure a long lifetime for electronics.…”