Interface Engineering Based on Polydopamine-Assisted Metallization in Highly Thermal Conductive Cellulose/Nanodiamonds Composite Paper

High thermal resistance frequently occurring at both filler–matrix and filler–filler interfaces lays down paramount bottlenecks for thermal management materials (TMMs). Herein, pony-size silver (Ag, 2–8 nm) nanoparticles are first constructed on nanodiamonds (NDs) with the assistance of environment-friendly polydopamine (PDA), which is rather different from larger Ag nanoparticles (AgNPs, 10–25 nm) simply deposited on NDs. Such ternary heterostructures impart low interfacial thermal resistance in cellulose nanofiber (CNF) composites and thereby allow high thermal conductivity but electric insulation. It is worth noting that the interfacial thermal resistance of CNF/Ag-PDA-ND (4.11 × 10–7 m2 K W–1) is exceptionally 1–2 orders of magnitude lower than those of CNF/Ag-ND (7.28 × 10–6 m2 K W–1) and CNF/ND (5.14 × 10–5 m2 K W–1) mainly due to the improved contact area between NDs assisted by PDA-Ag and even the bridging effect of AgNPs between NDs and CNFs. Of particular interest is our first establishment of an excellent heat interface (94.4% reduction in interfacial heat resistance) by introducing environment-friendly PDA during the metallization process rather than the reducing agent. With the appearance of such ternary heterostructures, the in-plane thermal conductivity of CNF/Ag-PDA-ND composite papers is high up to 16.36 W m–1 K–1 with about 1202% enhancement, compared to that of pure CNF. Meanwhile, the flexible CNF/Ag-PDA-ND composite papers are also endowed with high strength and toughness. Therefore, interfacial engineering can be extended to diverse materials (e.g., metallic oxides, carbon, and polymers) and can open creative avenues for sustainable high-performance TMMs in advanced high-power electronics.