Preparation of h-BN microspheres for nanocomposites with high through-plane thermal conductivity

In recent times, electronics have been increasingly minimized, and hence, heat dissipation has become essential. Owing to its high thermal conductivity and superior electrical insulation, hexagonal-boron nitride (h-BN) has been regarded as an appropriate ceramic material to increase the thermal conductivity of polymer nanocomposites for effective heat dissipation. However, the poor through-plane thermal conductivity of h-BN severely restricts its practical uses, and it is favorable for heat to radiates in the in-plane direction. In this study, densified spherical h-BN (sph-BN) microspheres, composed of as-synthesized nano-sized h-BN (nano-BN), were manufactured by a spray-drying process with variations in organic and/or inorganic binders followed by sintering. After incorporating various sph-BN particles as fillers into polydimethylsiloxane (PDMS), the through-plane thermal conductivity of composites embedded with sph-BN, assisted by a sodium silicate binder, enhanced the highest through-plane and in-plane thermal conductivities. The composites exhibited high thermal isotropy (through-plane thermal conductivity/in-plane thermal conductivity: lambda perpendicular to/lambda//${\lambda }_ \bot /{\lambda }_{//}$) of 0.77. The out-of-plane thermal conductivity of the composites was remarkably enhanced by over 2000% compared with pristine PDMS, which can be attributed to the synergy combined with the synthesis of the densified spherical BN initiated by nano-BN, sintering, and the application of inorganic binders. This study proposes a simple method to prepare polymer composites with h-BN that exhibit high through-plane thermal conductivity and are promising materials for heat removal in electronics.