Ultrathin flexible reduced graphene oxide/cellulose nanofiber composite films with strongly anisotropic thermal conductivity and efficient electromagnetic interference shielding
With the extensive use of portable and wearable electronic devices, ultrathin electromagnetic interference (EMI) shielding materials with excellent thermal management are increasingly desirable. In this study, ultrathin and highly aligned reduced graphene oxide (RGO)/cellulose nanofiber (CNF) composite films with excellent EMI shielding performance and strong anisotropy of thermal conductivity were fabricated by vacuum-assisted filtration followed by hydroiodic acid (HI) reduction. The obtained 50 wt% RGO/CNF composite films, which are only ≈23 μm in thickness, possess the remarkable electrical conductivity of ≈4057.3 S m−1 and outstanding EMI shielding effectiveness (SE) of ≈26.2 dB owning to the uniform dispersion and self-alignment into the layered structure of RGO. In addition, the RGO/CNF composite films with 50 wt% RGO loadings possess high in-plane thermal conductivity (K ≈ 7.3 W m−1 K−1) and, unexpectedly, very low cross-plane thermal conductivity (K⊥ ≈ 0.13 W m−1 K−1), resulting in strong anisotropy of the thermal conductivity (K/K⊥ ≈ 56). Thus, these ultrathin RGO/CNF composite films have great application potential as effective lightweight shielding materials against electromagnetic microwaves and heat, especially in flexible portable electronic devices and wearable devices.