Direct construction of interconnected Si3N4 nanowire networks for enhancing the thermal conductivity and mechanical performance of flexible composite films

Abstract

With great advancements in foldable electronic devices, there has been growing interest in ultra-light and flexible composite films possessing high in-plane thermal conductivity. One-dimensional (1D) Si₃N₄ nanowires (Si₃N₄NWs) possess the advantages of high thermal conductivity, superior mechanical performance and easy to be directionally aligned to construct thermally conductive pathways, which have been considered one of the ideal fillers for preparing anisotropic composite films. However, 1D Si₃N₄NWs with high aspect ratios tend to aggregate and are difficult to be dispersed in polymer matrixes, while traditional dispersion approaches utilizing prolonged ball milling or strong mechanical mixing easily result in a significant reduction in the length of Si₃N₄NWs, making it difficult to fully exploit the advantages of high intrinsic thermal conductivity. Therefore, it is highly essential to prepare high-performance composite films without damaging the length of Si₃N₄NWs. In this study, we propose an innovative strategy for the direct construction of continuous thermally conductive networks composed of ultra-long Si₃N₄NWs. An entire piece of Si₃N₄NW paper was successfully synthesized, which was directly used to prepare composite films via a simple vacuum-impregnation combined with hot-pressing method. Since the high aspect ratio of Si₃N₄NWs was maximally preserved during the composite process, the prepared Si₃N₄NW/EP composite films exhibited a high in-plane thermal conductivity of 16.02 W m⁻¹ K⁻¹ at a filling fraction of 64.6 wt%. More importantly, the interconnected, ultra-long Si₃N₄NWs also provide composite films with flexibility and excellent mechanical strength, enabling promising applications in the thermal management of electronic devices.