Rheological behaviour of IoNanofluids based on [emim][DCA] and [emim][TCM]

The viscosity of ionanofluids consisting of the two ionic liquids (ILs), 1-Ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) and 1-Ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM]), and aluminium oxide and magnesium oxide nanoparticles has been measured. The pure ionic liquids were also measured, and a simple Andrade equation and a Vogel-Tammann-Fulcher equation were presented to predict the temperature dependency of the ILs' viscosity with a good accuracy for both fluids (R-2 > 0.99). The measurements for both the pure ILs as well as the ionanofluids were performed over the temperature range of 295.15-353.15 K. The rheological behaviour was also examined for ILs as well as for the ionanofluids. For the ionanofluids two different particle sizes were investigated to see if a general trend could be found which was applied to both the bulk liquids. Yet this was not the case. The pure ILs were found to be perfectly Newtonian which supports the research data of other research groups. The ionanofluids were found to consist of a mixture of Newtonian and non-Newtonian fluids. All the non-Newtonian fluids displayed pseudoplastic behaviour which was determined through the Power Law Index as well as visual examination of graphs displaying the viscosity along various shear rates. Both theoretical and empirical models were applied to the ionanofluids to examine if the prediction would match the measured data, though the predictions were not accurate. The effect of time was also investigated using hysteresis-loops at various temperatures as well as extended measurements where the samples were heated and cooled. Time dependency was not found in the classical form of thixotropy or rheopexy but a trend of increasing viscosity at sufficiently low shear rates and high temperatures was detected. These are believed to be due to changes of the internal structure that the nanoparticles assemble within the fluid. (C) 2021 Published by Elsevier B.V.

Automated summary

The viscosity of ionanofluids consisting of two ionic liquids and nanoparticles has been measured, and equations have been proposed to predict the temperature dependency of the liquid's viscosity. The pure ionic liquids were Newtonian fluids, while the ionanofluids showed a mixture of Newtonian and non-Newtonian behavior, with increasing viscosity at low shear rates and high temperatures. The accuracy of the prediction models needs improvement.