Flexible, thermally conductive layered composite films from massively exfoliated boron nitride nanosheets

Abstract Flexible, electrically insulating and highly thermally conductive materials are desired in the thermal management application of next-generation electronic devices. In this work, bulk boron nitride are exfoliated in N-methyl-2-pyrrolidone solvent through a unique combination of large and small ball milling, generating large-volume dispersion with plane defect-free, few-layered boron nitride nanosheets. The exfoliated dispersion is concentrated through centrifugation and further processed into large-area, layered composite films with poly(vinylidene fluoride) through a scalable doctor-blading technique. The high quality of boron nitride nanosheets and their well-ordered layered arrangement imparts the composite film with high in-plane thermal conductivity and low through-plane thermal conductivity. With incorporation of 60 wt% boron nitride nanosheets, the in-plane thermal conductivity is as high as 11.88 W/m K, two orders of magnitude larger than neat poly(vinylidene fluoride). The through-plane thermal conductivity is only 0.41 W/m K, about the same as neat poly(vinylidene fluoride). Besides, the composite film is highly flexible and can be folded without fracture.