We report for the first time the preparation of highly stable graphene (GE)-based nanofluids with ionic liquid as base fluids (ionic liquid-based nanofluids (Ionanofluids)) without any surfactant and the subsequent investigations on their thermal conductivity, specific heat, and viscosity. The microstructure of the GE and MWCNTs are observed by transmission electron microscope. Thermal conductivity (TC), specific heat, and viscosity of these Ionanofluids were measured for different weight fractions and at varying temperatures, demonstrating that the Ionanofluids exhibit considerably higher TC and lower viscosity than that of their base fluids without significant specific heat decrease. An enhancement in TC by about 15.5% and 18.6% has been achieved at 25 °C and 65 °C respectively for the GE-based nanofluid at mass fraction of as low as 0.06%, which is larger than that of the MWCNT-dispersed nanofluid at the same loading. When the temperature rises, the TC and specific heat of the Ionanofluid increase clearly, while the viscosity decreases sharply. Moreover, the viscosity of the prepared Ionanofluids is lower than that of the base fluid. All these advantages of this new kind of Ionanofluid make it an ideal fluid for heat transfer and thermal storage.

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Highly thermally conductive, electrically insulating, and flexible nanocellulose composite films are crucially significant for the thermal management of next-generation green electronics. However, the intrinsic hygroscopicity of nanocellulose poses a daunting challenge to the reliability and structural stability of electronic products. To address these issues, herein, a dual bioinspired design was innovatively introduced to fabricate highly thermally conductive and superhydrophobic nanocellulose-based composite films via vacuum-assisted self-assembly of cellulose nanofibers (CNFs) and hydroxylated boron nitride nanosheets (OH-BNNS) and subsequent hydrophobic modification. Driven by the highly orderly hierarchical architecture and a strong hydrogen bonding interaction, the laminated CNF-based composite films with 50 wt % OH-BNNS show a high in-plane thermal conductivity (15.13 W/mK), which results in a 505% enhancement compared with the pure CNF films. On the other hand, the rough surface combined with a low surface energy modifier endows CNF/OH-BNNS composite films with unique superhydrophobicity (contact angle over 155°) and a simultaneous self-cleaning function. Furthermore, the as-fabricated multifunctional CNF/OH-BNNS composite films were designed as a flexible printed circuit board to simulate the potential applications in the field of cooling electronic devices. The development of CNF/OH-BNNS composite films with synergetic properties of high thermal conductivity and superhydrophobicity may shed light on the functional thermal management materials and offer an innovative insight toward fabricating multifunctional nanocomposites via a dual bio-inspired design.

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