Investigation on the rheological behavior of coconut oil based hybrid CeO 2 /CuO nanolubricants

In the present work, hybrid CeO₂/CuO–coconut oil nanolubricants in different weight fractions are prepared for different proportions of CeO₂ and CuO namely 25/75, 50/50, and 75/25. Experimental and theoretical studies are carried out to investigate the rheological behavior of these hybrid nanolubricants with different proportions CeO₂/CuO at a temperature range of 30 ℃ to 90 ℃ and various shear rates for different total concentrations (wt%) ranging from 0% to 1%. For higher concentrations and lesser shear rates, non-Newtonian behavior is observed for each proportion of CeO₂ and CuO. Nanoparticle–oil interactions play an important role for non-Newtonian behavior at higher concentrations. But at higher shear rates, the nanolubricants behave as Newtonian fluids at all temperatures and concentrations. The values of viscosity measured using a rheometer shows minor variations compared to the values obtained by the theoretical models due to interactions, morphology, and size effects of nanoparticles. An empirical viscosity prediction model for hybrid CeO₂/CuO–coconut oil nanolubricants is proposed in terms of concentrations for various temperatures and proportions of CeO₂/CuO nanoparticles based on experimental results.