H.B. Jiang, S. Mateti, Q.R. Cai,* H. Shao, S.M. Huang, Z.-S. Wu, C.Y. Zhi, Y. I. Chen*
Composites Science and Technology, 2022, 230, 109769.
DOI: 10.1016/j.compscitech.2022.109769 [PDF]
Heat dissipation has become a crucial issue in modern advanced electronics that are developed towards high integration, miniaturisation, light weight, and high power. Thanks to the high thermal conductivity yet excellent electrical insulation, hexagonal boron nitride (h-BN) has been considered as an ideal filler material to enhance thermal conductivity of polymer for efficient heat dissipation. However, its highly anisotropic thermal conductivity works unsatisfactory in some situations and a heat spreader that propagates heat along multiple directions is favourable. In this work, micrometre-sized, binder-free boron nitride spheres (BNSs) have been synthesised for the first time using a two-step process of thermal spray drying and high-temperature sintering at 2200oC. Consisting of randomly dispersed boron nitride nanosheets (BNNSs), the BNSs show an isotropic thermal conductivity of 34.8 W/mK.Using the BNSs as fillers, the enhancedpoly(vinyl alcohol) (PVA) films (~250 μm thick) have a quasi-isotropic thermal conductivity with an in-plane value of 10.6 W/mK and out-of-plane value of 8.1 W/mK at the BNSs loading of 52 vol%. The significant enhancement of about 3700% is attributed to the formation of isotropic thermally conductive networks within the polymer matrix and strong interactions between BNNSs inside BNSs. In addition, the potential application of the BNSs-enhanced PVA films in thermal management has been demonstrated. This study provides a practical route to fabricate BN-enhanced polymer films with isotropic thermal conductivity and promising materials that are valuable for new-era advanced electronic packaging and related applications.
