Optical, dielectric, and rheological properties of EG-Al2O3/AgNO3 nanofluids: Insights and advances in multifunctional materials for soft device technologies

Nanofluids (NFs) of fascinating multifunctional properties are the advanced materials highly admired in emerging soft device technologies. In this innovative research, we explored the detailed optical, dielectric, and rheological properties of silver ions conducting green NFs. These NFs comprise ethylene glycol (EG) as viscous base fluid, suspension of a fixed amount (0.02 wt%) aluminum oxide (Al 2 O 3 ) nanoparticles for high performance thermal conductor, and addition of silver nitrate (AgNO 3 ) salt as the ionic component of varying amounts ranging from 0.2 to 2.0 wt% are prepared and investigated. The detailed analysis of 200–800 nm wavelength range ultraviolet–visible (UV–Vis) absorbance spectra of these EG–Al 2 O 3 /AgNO 3 based NFs demonstrated their significant photosensitivity character in the visible region, radiations shielding performance in the UV region, and trio energy band gaps in a wide semiconducting range from 2.4 to 4.9 eV which are found adequately tunable with the AgNO 3 concentrations. The high static dielectric permittivity (ε s ≈ 40) of these polar NFs, at 298.15 K, showed a marginal change with the variation in AgNO 3 concentrations confirming a little alteration in the parallel aligned dipole ordering of hydrogen bonded EG molecular network beside the ion-molecules-nanoparticle interactions and formation of ion-dipole complexes (coordinative interaction). The electrical conductivity of EG–Al 2 O 3 NF increased by three orders of magnitude i.e., from 10 −6 to 10 −3 S/cm, at the initial addition of 0.2 wt% AgNO 3 in it and then, exhibited almost a linear increase with further increasing the salt concentrations up to 2.0 wt% realizes them promising ionic nanofluids. Rheological investigations on these NF samples, at 298.15 K, validate their Newtonian behaviour with a high dynamic viscosity of 14 mPa s. These experimental findings highlight the multifunctional characteristics of EG–Al 2 O 3 /AgNO 3 nanofluids which could be utilized in heat transfer, solar energy harvesting/storage, and the development of next-generation iontronic and optoelectronic devices and silver ion conducting biomedical sensors.