Interestingly, the nanofluids displayed pronounced thixotropic behavior, with clear hysteresis loops evident beyond the percolation threshold, indicating structure breakdown and time-dependent recovery. However, before the percolation threshold, no significant hysteresis loop was observed, nanofluids seem to exhibit a Newtonian nonthixotropic behavior. Flow behavior index analysis showed a shift from Newtonian to shear-thinning to complex non-Newtonian behavior with increasing concentration and temperature. Activation energy calculations further highlighted the evolving flow mechanisms under thermal stimuli.
These findings provide insights into the relationship between nanoparticle concentration, temperature, and fluid microstructure, particularly around the percolation threshold. The observed correlation between critical temperature, zeta potential inflection, and rheological response suggests a new pathway for designing intelligent, temperature-responsive nanolubricants. This work improves formulations that balance stability, flowability, and thermal performance in precision manufacturing, energy systems, and sustainable tribology.