Enhancing the thermal conductivity and dielectric properties of polymer composite film through segregated boron nitride nanosheets

High interfacial thermal resistance (ITR) between thermally conductive nanofillers and polymer matrix, and lack of good orientation of nanofillers are primary limiting factors in harnessing their inherent thermal conductivity in polymer nanocomposites. Thus, exploiting ultrahigh thermal conductivities of nanofillers involves developing methods or mechanisms that can minimize the ITR. In this work, boron nitride nanosheets (BNNS)/polyvinyl alcohol (PVA) nanocomposite films with segregation-induced interconnection among BNNS are fabricated by a sequential unidirection freeze-casting (UFC) technique. A PVA aerogel is first made by UFC followed by infiltrating functionalized BNNS into its pores and microchannels which is subjected to a second UFC process. The composite aerogel is subsequently hot pressed to compact the available pore channels for reduced ITR arising from better contact between the segregated BNNS cell walls. The resulting segregated BNNS/PVA (SBP) nanocomposite film with 40 wt% BNNS exhibits high thermal conductivity of 5.2 W/mK, which is about 267 % higher than the nanocomposite film containing dispersed BNNS made by conventional UFC. The SBP film also possessed high electrical insulation characteristics and a very low dielectric loss of 10^-2 at a frequency of 1 kHz, properties arising directly from the segregated BNNS. The sequential UFC provides an effective method to incorporate aligned and interconnected BNNS through segregation for enhanced thermal conductivity and electrical resistivity for thermal management in microelectronics and integrated circuits.