Largely improved thermal conductivity of PI/BNNS nanocomposites obtained by constructing a 3D BNNS network and filling it with AgNW as the thermally conductive bridges

Polyimide (PI) is an essential substrate or packaging material for various electronic devices. The decreased packaging size and high integration in electronic systems have caused the issue of heat accumulation issue. However, the intrinsic low thermal conductivity of PI cannot meet the requirements of certain electronic systems. Herein, we report a facile and effective approach to fabricating highly thermally conductive polyimide (PI)-based composites by constructing 3D nanofiller segregated networks in the matrix and realizing reduced interfacial thermal resistance between adjacent nanofillers. First, a water-soluble poly(amic acid) tertiary amine salt was utilized as a surfactant to facilitate the dispersion of hydrophobic boron nitride nanosheets (BNNS) in aqueous phase. Then, a combination of the ice-templating strategy and a hot-pressing treatment was applied to control the oriented distribution of BNNS, and the silver nanowires (AgNW) were incorporated and acted as thermally conductive bridges, resulting in an obvious decrease of thermal interfacial resistance and forming an interconnected thermally conductive expressway. Thus, a significant improvement in the thermal conductivity was achieved. The resultant nanocomposite with 20 wt% BNNS-AgNW exhibited an in-plane thermal conductivity of 4.75 W m(-1) K-1, corresponding to a thermal conductivity enhancement of 324%, which is much superior to those of the pure PI and the random distribution composites. These nanocomposites present an excellent electrically insulation property and good dielectric behavior as well as improved dimensional stability. This facile methodology is believed to afford PI-based materials broad application potential used as thermal interface materials in next generation electronic devices.