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The developments in the high-power densities and high integration of electronic devices have put forward higher requirements for advanced thermal management materials (TMMs) to meet the rising demand for heat dissipation. However, it has remained a major challenge to achieve significant enhancement of thermal conductivity (TC) of TMMs without compromising their mechanical and dielectric properties. Here, we report a flexible, thermally conductive composite film that contain aramid nanofiber (ANF) and silver nanoparticles (AgNPs) decorated with boron nitride (BN), the in-plane TC of which is up to 12 W/mK at 40 wt.% filler contents. Such a high TC is attributed to the bridging role of AgNPs, which greatly reduces the interfacial thermal resistance of composites. At the same time, the as-prepared composite films possess outstanding mechanical strength (>126 MPa), owing to the coupling between the ANF network and the favourable hydrogen bonding interaction between the ANF and the functional BN. Moreover, a low dielectric loss (<0.05), high electrical resistivity (~1014 Ω·cm), and high decomposition temperature (>500°C) are simultaneously achieved for the composite films. These findings offer a facile strategy for the design of multifunctional TMMs, which hold great promising for application in electric devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A composite paper was prepared by combining aramid nanofibers, boron nitride nanotubes, and polyethyleneimine. • Elaborating interfacial hydrogen bonds design can optimize the mechanical properties of composite paper. • The composite paper has high thermal conductivity and unique dielectric performance. Aramid paper is ubiquitous in advanced electronics and high-voltage equipment by virtue of their outstanding dielectric properties, mechanical reliability, and thermal stability. However, their limited thermal conductivity still fails to satisfy the stringent demands for heat dissipation in applications with high power and high energy density. Herein, we report a highly thermally conductive composite paper prepared by synergistically combining one-dimensional (1D) aramid nanofibers (ANFs), 1D edge-hydroxylated boron nitride nanotubes (BNNTs), and polyethyleneimine (PEI). The resultant composite paper exhibits high thermal conductivity (9.91 Wm−1K−1), low dielectric loss (<0.01), and ultrahigh electrical breakdown strength (∼334 kV/mm) with an exceptional heat resistance performance. Three-dimensional hydrogen bonding networks were constructed between the ANF framework, PEI, and BNNTs, endowing the composite paper with a superior tensile strength (up to 317 MPa) and Young's modulus (∼7.7 GPa), which are significantly higher than those of the commercial Nomex T410 paper. This research provides important insights into the design and fabrication of multifunctional insulating paper for application in modern integrated electronic and power systems. [ABSTRACT FROM AUTHOR]