Investigation on stability, density and viscosity of ZnO/PEG nanofluids in the presence of 1-butyl 3-methylimidazolium chloride and 1-butyl 3-methylimidazolium bromide ionic liquids

Abstract

Addition of ionic liquids (ILs) into the fluids containing nanoparticles is often used to minimize particle aggregation and improve dispersion behavior of nanofluids. However, they also affect the physical characteristics of liquids, such as thermophysical properties and viscosity. The aim of this work was to investigate the role of 1-butyl 3-methylimidazolium bromide [C₄mim][Br] and 1-butyl 3-methylimidazolium chloride [C₄mim][Cl] on the dispersion stability, volumetric characterizations and viscosity of polyethylene glycol 200 (PEG 200) nanofluids containing ZnO nanoparticles. Particle size distribution of these nanofluids has been studied by UV–Vis spectroscopy and dynamic light scattering (DLS). The obtained results show that the nanofluids with PEG 200 + [C₄mim][Cl] have lower stability than PEG 200 + [C₄mim][Br]. Additionally, in order to understand molecular interactions between components of studied nanofluids (ZnO, PEG 200 and ILs) the density (d), speed of sound (u) and viscosity ($\eta$) of these nanofluids were measured at 293.15, 298.15, 308.15 and 308.15 K. The excess molar volume ($V_{m}^{E}$), apparent molar volume ($V_{\phi }$) and isentropic compressibility ($\kappa_{s}$) have been calculated using density and speed of sound data. These properties can help us to discuss about the stability and volumetric characterizations of the nanofluids. Also, theoretical analyses of $V_{m}^{E}$, $\kappa_{s}$ and $\eta$ were performed using some existing models (Ott et al., Redlich–Kister, Eyring-mNRF and Eyring-NRTL) and the obtained results were compared with experimental data.