Silicone oil-based solar-thermal fluids dispersed with PDMS-modified Fe3O4@graphene hybrid nanoparticles

One of the most challenging problems that limit the practical application of carbon-based photothermal nanofluids is their poor dispersion stability and tendency to form aggregation. Herein, by using Fe3O4@graphene hybrid nanoparticles as a model system, we proposed a new method to prepare stably dispersed silicone oil-based solar-thermal nanofluids that can operate at high temperatures than water-based fluids. The introduction of Fe3O4 nanoparticles between graphene nanosheets not only physically increases the inter-plane distance of the graphene nanosheet but also provides numerous anchoring points for surface modification. Phosphate-terminated polydimethylsiloxane chains, which have high compatibility with the silicone oil base fluids and high-temperature stability, were synthesized and utilized to modify the Fe3O4 nanoparticle surfaces. The attached chains create steric hindrance and effectively screen the strong inter-plane van der Waals attraction between graphene sheets. Dispersion stability of the nanofluids with different concentrations of surface-modified hybrid nanoparticles and heated under different temperatures was investigated. We have demonstrated that such fluids could maintain stable dispersion under a heating temperature up to 150 °C depending on the concentration of the hybrid nanoparticles. The resultant nanofluids maintained stable dispersion after repeated heating and were employed for consistent direct solar-thermal energy harvesting at 100 °C. Keywords: Silicone oil, Graphene, Nanofluid, Dispersion, Solar-thermal energ