Effect of nanodispersed zinc oxide concentrations on the structural, optical, dielectric, viscous, and acoustic properties of ethylene glycol– glycerol mixture based nanofluids

Abstract

Nanofluids (NFs) are green-formulated innovative soft materials, enormously used for thermal management medium in energy harvesting/ storage and heat transport, as high breakdown voltage insulators/ nanodielectrics in electrical and energy storage systems, and in the advances of soft condensed matter device technologies. In this study, NFs consisting of ethylene glycol (EG) and glycerol (Gly) mixture in equal volumes as the base fluid and semiconductive zinc oxide (ZnO) nanoparticles with increasing concentrations from 0.005 to 1.00 wt% are prepared and characterized by employing different advanced techniques. X-ray diffraction (XRD) patterns recorded directly on these NFs confirmed the homogeneity and nanosuspension stability of ZnO particles in the hydrogen-bonded supramolecular 3D structure of viscous EG–Gly base fluid. The UV-Vis absorbance spectra explained the ZnO concentration tunable photo sensing and UV blocking properties of these semiconductive nanofluids. The 20 Hz to 1 MHz range dielectric spectra revealed high static dielectric permittivity of these NFs, at 298.15 K, confirming them as promising nanodielectric for electric energy storage devices. The dielectric dissipation factor, electric modulus, and impedance spectra confirmed that these EG–Gly/ZnO NFs have electrode polarization and conductivity relaxation processes around 200 Hz and 20 kHz, respectively. The electrical conductivity is observed in the range of 0.32– 0.65 μS/cm with a noticeable increase at the higher ZnO concentration which infers appreciable insulation performance of these NFs. The rheological measurements demonstrated Newtonian behavior of these NFs with a dynamic viscosity of about 69 mPa.s, at 298.15 K. Ultrasound velocity and various acoustic parameters of these NF materials are marginally altered with varying the ZnO concentration and revealed appreciable thermal conductivity of 0.31 W·m–1·K–1, at ambient temperature. The temperature dependent viscosity measurements of EG–Gly/1.00 wt% ZnO sample demonstrated its Arrhenius behavior with high activation energies for both the viscous and relaxation processes. These experimental results establish the EG–Gly/ZnO nanofluids as multifunctional materials for highlighting current applications and also in futuristic soft condensed matter technologies.