The Density, Speed of Sound, Viscosity, and Thermal Conductivity of 1-Dodecyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide and Its Ionanofluid with Graphene

The ionic liquid 1-dodecyl-3-methyl-imidazolium bis(trifluoro-methyl-sulfonyl)imide, termed [C(12)mim][(CF3SO2)(2)N], has been studied for several applications, such as gas solubility, phase equilibrium studies in binary and ternary systems, the separation of butan-1-ol/water, and thermal energy storage, with studies on its nanostructure and thermophysical properties having been performed. The main justification for these studies is that increasing the length of the carbon chain also increases the heat capacity, which endows [C(12)mim][(CF3SO2)(2)N] with excellent thermal properties. These thermal properties make [C(12)mim][(CF3SO2)(2)N] a strong potential choice for use as the thermal energy storage (TES) and heat transfer fluid (HTF) media in solar thermal power plant systems, especially when compared to traditional media (i.e., thermal oils). In order to confirm this possibility, in this study we measured the density, speed of sound, viscosity, and thermal conductivity of [C(12)mim][(CF3SO2)(2)N] in the temperature range 293.15 < T/K < 343.15 and at P = 0.1 MPa. In addition, we studied its ionanofluid with graphene by measuring its viscosity and thermal conductivity (for the first time), aiming to confirm to the fact that long alkyl chains in alkylimidazolium liquids may improve the stabilization of the nanoparticle dispersion in the nanofluid. Our results demonstrate that [C(12)mim][(CF3SO2)(2)N] and its ionanofluid with graphene are both Newtonian fluids. It was also determined that the transport properties of [C(12)mim][(CF3SO2)(2)N] are not affected (within the mutual uncertainty of the experiments) by the presence of nanographene platelets in a stable dispersion.