Micro-diamond assisted bidirectional tuning of thermal conductivity in multifunctional graphene nanoplatelets/nanofibrillated cellulose films

Environmentally friendly thermal interface materials (TIMs) with bidirectional high thermal conductivities have aroused considerable interests for addressing the heat dissipation issue in integrated circuits. Although graphene-based TIMs exhibit excellent in-plane thermal conductive performance, their through-plane thermal conductivity is commonly less than 3 Wm(-1)K(-1) owing to the vast interfacial phonon scattering, significantly limiting their practical applications. In this study, a strategy aimed at building TIMs with controllable heat transfer pathways both along the in-plane and through-plane directions is proposed by incorporating micron-diamonds (MDs) in graphene nanoplatelets/nanofibrillated cellulose (GNPs/NFC) composite film via a facile and green self-assembly method. The morphology of the obtained MDs@GNPs/NFC composite film can be precisely tailored from a hierarchical structure to a 3D solid foam-like structure to tailor heat transfer paths. By adjusting the loading and particle size of MDs, a through-plane thermal conductivity of 8.85 Wm(-1)K(-1) was achieved accompanied with a simultaneously high in-plane thermal conductivity of 32.01 Wm(-1)K(-1). The excellent bidirectional thermal conductive performance is integrated with high-efficiency Joule heating capability, outstanding nonflammability, as well as superior electromagnetic shielding performance, showing a promising future in advanced electronic devices. (C) 2021 Elsevier Ltd. All rights reserved.