Molecular engineering of the surface of boron nitride nanotubes for manufacture of thermally conductive dielectric polymer composites

Recent developments in microelectronic devices have led to rising demand for polymeric nanocomposites that can simultaneously deliver enhanced thermal conduction and electrical insulation. Boron nitride nanotube (BNNT) is one of the most promising fillers for the fabrication of such composites. While being electrically insulating, effective crystal lattice vibrations allow BNNTs to achieve thermal conductivity values that can even surpass that of diamond. However, when BNNTs are surface functionalized and incorporated within polymers, their lattice vibrations are significantly suppressed, resulting in polymeric nanocomposites with thermal conductivity values only a fraction of what BNNTs can achieve in air. The aim of this study is to shed light on the underlying cause of this challenge for thermally conductive, dielectric polycarbonate (PC)/BNNT nano composites that were produced using two distinct surface functionalization approaches. By incorporation of BNNTs in PC, the thermal conductivity values were significantly increased. However, depending on nanotubes' concentration, the thermal conductivity of pristine BNNTs in PC were comparable or superior to those of the functionalized nanotubes. Theoretical analysis and experimental characterization have been conducted to elucidate the fundamental impacts of surface functionalization on the lattice vibrations of BNNTs and their subsequent effects on the thermal properties of dielectric BNNT composites.