Effect of metal ion coordination bond on the thermal conductivity of cellulose nanofibrils

To address the diversified thermal management requirements of flexible electronic devices, there is an urgent need to develop flexible materials that combine excellent mechanical properties with on-demand tunable thermal conductivity, thereby enabling efficient thermal design and structural–functional integration. Cellulose nanofibrils (CNFs) are an eco-friendly, high-strength material with tunable thermal conductivity, showing considerable potential. To better harness this potential, a deeper understanding of how different bonding forms affect their intrinsic thermal conduction and the underlying regulatory mechanisms is required. To this end, this study employs a self-designed flow-focusing assembly system to systematically investigate the regulatory effects of synergistic bonding networks on the thermal conductivity of materials by controlling the concentration of multivalent metal ions that induce CNF gelation. This approach enables continuous adjustment of the thermal conductivity of CNF films within the range of 0.241–0.758 W m−1 K−1. Raman spectroscopy and micro-Fourier transform infrared analyses indicate that the role of multivalent metal ions primarily stems from a triple mechanism: the reduction of crystallinity, which shortens phonon mean free paths; the competitive reconstruction of bonding networks, where moderate ion addition strengthens hydrogen bonding, while higher concentrations promote coordination-dominated regimes; and the introduction of structural heterogeneities—such as phase boundaries in Mg2+-induced gels and point defects in Fe3+-crosslinked networks—that intensify phonon scattering and collectively govern thermal transport. This study reveals the structure–property relationship between ion-mediated microstructural evolution and thermal transport in CNFs, providing insights for the design of high-performance CNF materials for intelligent thermal management applications.