Effects of PVP surfactant on nanosuspension stability and optical, dielectric, and rheological properties of zinc oxide nanoparticles dispersed alcohols mixture based nanofluids

Abstract

Nanofluids (NFs) are state-of-the-art engineered promising properties soft materials which found vital applications in thermal management and electrical insulation, and also gaining much attention in the advances of soft optoelectronic and microelectronic device technologies. The longer-time functionality of the NF material depends on particle suspension stability which can be maintained up to some extent with the addition of appropriate surfactants. Here, we report the promising properties of the semiconductor NF (SNF) samples consisting of a highly rich ethylene glycol (EG) mixture with glycerol (Gly) (90/10 vol%) as base fluid, zinc oxide (ZnO) nanosuspension, and poly(vinyl pyrrolidone) (PVP) surfactant. These formulated 90EG + 10Gly/x wt% (ZnO + PVP) SNFs with varying concentrations (x wt%) of ZnO and PVP are characterized by employing ultraviolet-visible (UV–Vis) spectrophotometer (wavelength range 200–800 nm), precision inductance-capacitance-resistance (LCR) meter (frequency range 50 Hz to 1 MHz), and rotational rheometer (shear rate range 13–132 s−1). The UV–Vis absorbance spectra, recorded on the freshly prepared and aged SNF samples, confirmed that the added PVP enhances longer time suspension stability for ZnO nanoparticles in the H-bonded 90EG + 10Gly viscous base fluid, and also promoted the photosensitivity, electronic transition, and radiation blocking performance of these materials. The dielectric spectra revealed a huge contribution of the electrode and interfacial polarization processes to the dielectric permittivity of the SNFs at low frequencies and their dynamics is explored from the intense relaxation peaks observed in the loss angle tangent spectra. The higher experimental frequency range dielectric permittivity remains frequency independent and it is marginally affected by the ZnO and PVP concentrations in these SNFs, at 298.15 K. The electric modulus and impedance spectra of these SNFs are also provided and analyzed for the charge conductivity and interfacial relaxation processes. The ac electrical conductivity of these materials obeys the power law behaviour along with the dc conductivity part in the range from 5.4 to 6.8 × 10–7 S⋅cm−1. The rheological measurements on these SNFs, in the 303.15 K to 323.15 K, categorized them as Newtonian-type fluids with a considerable increase in dynamic viscosity by PVP dissolution. These materials showed the Arrhenius behaviour of viscous flow having activation energies in the range of 25–27 kJ⋅mol−1. The experimental results of various techniques on these green-formulated SNFs revealed their multifunctionality with great potential for the future generation of soft device technologies, in addition to highlighting their current applications of manageable heat transfer in the flow systems.