An Anisotropically High Thermal Conductive Boron Nitride/Epoxy Composite Based on Nacre‐Mimetic 3D Network

Abstract

Polymer-based thermal interface materials (TIMs) with excellent thermal conductivity and electrical resistivity are in high demand in the electronics industry. In the past decade, thermally conductive fillers, such as boron nitride nanosheets (BNNS), were usually incorporated into the polymer-based TIMs to improve their thermal conductivity for efficient heat management. However, the thermal performance of those composites means that they are still far from practical applications, mainly because of poor control over the 3D conductive network. In the present work, a high thermally conductive BNNS/ epoxy composite is fabricated by building a nacre-mimetic 3D conductive network within an epoxy resin matrix, realized by a unique bidirectional freezing technique. The as-prepared composite exhibits a high thermal conductivity (6.07 W m −1 K −1 ) at 15 vol% BNNS loading, outstanding electrical resistivity, and thermal stability, making it attractive to electronic packaging applications. In addition, this research provides a promising strategy to achieve high thermal conductive polymer-based TIMs by building efficient 3D conductive networks.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201900412. graphene [12] (1-16 W m −1 K −1 ), and carbon nanotubes [13] (CNTs, 0.5-5 W m −1 K −1 ) are usually included in the polymer matrix. Among all those fillers, boron nitride (BN) is particularly outstanding for its high thermal conductivity, excellent electrical insulation, and low cost. [14] During the last decade, although many efforts have been made to develop BN-based polymer composite, [15][16][17][18] its real application as TIM is greatly hindered for its moderate thermal conductivity. This could be mainly attributed to the insufficient manipulation of the 3D conductive network. For the same reason, currently reported composites are usually thin films although there is an urgent need for bulk BN-based composite with high thermal conductivity.Here, a BN/epoxy composite with a nacre-mimetic 3D conductive network was constructed by a bidirectional freezing technique. [19][20][21] The boron nitride nanosheets (BNNS) were assembled into an aerogel with long-range aligned lamellar layers, followed by infiltration of epoxy resin. The highly organized 3D conductive network provides prolonged phonon pathways, yielding a much higher thermal conductivity (6.07 W m −1 K −1 ) at a relatively low BN loading (15 vol%) comparing to the similar composites in the literature. Together with its excellent electrical resistivity (2 × 10 12 Ω cm) and thermal stability (glass transition temperature: 120 °C), our composite may find wide applications including TIM for the advanced electronic packaging technology. Keywords3D conductive network, bidirectional freezing, boron nitride, long-range lamellar structure, thermal interface material

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

“…Such anisotropy was commonly observed in composite films containing highly aligned 2D fillers, allowing a directional thermal dissipation capability in the filler alignment direction. [ 22 ] By introducing rGO layers between the BNNS layers (at an rGO to BNNS weight ratio of 1) while keeping the total filler contents identical to the BNNS‐PI composites, the thermal conductivities of micro‐sandwich composites further improved by 30–70% against those containing BNNS alone. The thermal conductivities of BNNS‐PI and rGO‐PI/BNNS‐PI composites were compared with their counterparts containing randomly dispersed (hollow symbols) [ 1,47–49 ] or 3D interconnected fillers (solid symbols) [ 22,50,51 ] in Figure 5a.…”

“…[ 5,16–20 ] Graphene and hexagonal boron nitride (h‐BN) with high thermal conductivities are effective fillers to mitigate the poor thermal management capabilities of composites by upgrading thermal conductivities to over 1 W m −1 K −1 . [ 21–23 ] Despite their similar thermal properties, the electrical conductivities of graphene and h‐BN are completely different, [ 24 ] leading to different dielectric properties of composites made therefrom. Electrically conductive reduced graphene oxide (rGO) significantly improved the dielectric constants of composites at low filler loadings, thanks to the low percolation thresholds arising from their high aspect ratios.…”

Thermal Transport in 3D Nanostructures

“…Take the epoxy composite with nacre‐mimetic 3D BN network as an example, its thermal conductivity in the parallel direction to the lamellar layer (cross‐plane) appears sensitive to the temperature, which increases from 6.07 to 8.41 W m −1 K −1 when the temperature increases from 20 to 100 °C. However, in the perpendicular direction (in‐plane), κ is insensitive to temperature . Comparing with the composite with randomly dispersed BNNS, a stronger temperature dependency of κ is observed for the composite with 3D BN networks.…”

“…Comparing with the randomly dispersed BNNSs, the 3D BN network shows much stronger enhancement to the heat transfer in the polymer composite . Depending on the fabrication approach, the 3D BN network can also endow the polymer composite with a tailorable anisotropic thermal conductivity . Figure e summarizes the thermal conductivity of different polymer composites reinforced by 3D BN networks.…”

Bioinspired Biomaterials with a Brick‐and‐Mortar Microstructure Combining Mechanical and Biological Performance

“…Recently, bidirectional freezing technique, using the bidirectional temperature gradients, has been successfully demonstrated to prepare large scale 3D lamellar bulk exceeding centimeter dimensions. Han et al took advantage of bidirectional freezing technique to prepare an anisotropic BN/epoxy composite with high thermal conductivity . The method paved the way for fabricating high thermal conductive material by designing novel 3D networks.…”