Graphene-based nanofluids: A comprehensive review about rheological behavior and dynamic viscosity

Abstract Graphene derivatives are promising nanomaterials for producing nanofluids due to their excellent intrinsic characteristics. Among thermophysical profile, and in addition to thermal properties, relevant property to evaluate the potential of graphene-based nanofluids as efficient and reliable heat transfer fluids is viscosity, and rheological behavior in a wider sense. Therefore, the aim of this review paper is to give a comprehensive overview of the current knowledge and results about the rheological properties of graphene-based nanofluids. After a brief description of the most common methods used for fabricating or extracting graphene derivatives, the main steps of graphene-based nanofluids preparation are introduced. Then, literature results on Newtonian/non-Newtonian behavior as well as variations in apparent dynamic viscosity of suspensions containing graphene derivatives are reviewed, analyzing the effects of shear rate, concentration, base fluids and temperature. Such an analysis is performed distinguishing the different types of graphene derivatives, namely graphene oxide, reduced graphene oxide, pristine graphene, graphene quantum dots, functionalized and doped graphene. Also, the impact of base fluid, temperature, concentration and surfactant on viscosity enhancement of graphene-based nanofluids is graphically and newly presented and discussed. In addition, the current models for viscosity prediction or correlation of those nanofluids are detailed. Finally, challenges and future works are summarized.