Flexible cellulose nanofiber/graphene films with liquid metal-filled microvoids for enhanced thermal management and electromagnetic interference shielding

Abstract

Flexible, ultra-thin thermal conductive materials with highly efficient electromagnetic interference (EMI) shielding are urgently needed for next-generation wearable electronics. However, simultaneously achieving flexibility, high-performance EMI shielding, and efficient thermal conductivity via a simple and scalable manufacturing process remains challenging. Inspired by powder metallurgy compaction densification, we fabricated a flexible cellulose nanofiber/liquid metal/graphene nanoplatelets (CNF/LM/GNPs) composite film by incorporating a flowable LM into a CNF/GNPs matrix via vacuum-assisted filtration followed by cold-pressing processes. Benefiting from the exceptional electrical/thermal conductivity and unique fluidity of the LM, the LM effectively permeates gaps between adjacent GNPs and the CNF matrix, establishing a continuous thermal conductive network while enhancing densification. Consequently, the composite film exhibits outstanding in-plane (16.41 W m⁻¹ K⁻¹) and through-plane (1.21 W m⁻¹ K⁻¹) thermal conductivity, enabling efficient thermal management. Finite element simulations confirm that LM droplets between adjacent GNPs facilitate continuous thermal pathways, providing additional phonon transport channels. Additionally, the film achieves high electrical conductivity (509.6 S m⁻¹) and exceptional EMI shielding effectiveness (35.90 dB). Notably, the CNF/LM/GNPs films demonstrate a tensile strength of 40.26 MPa and an elongation at break of 17.32%, meeting diverse environmental application requirements. This work proposes a novel strategy for designing flexible composite films with simultaneous superior thermal conductivity and high-efficiency EMI shielding performance.