(226b) Thermorheological Transitions of Graphene Nanofluids in High Oleic Soybean Oil Near Percolation Threshold

Understanding the thermorheological behavior of nanofluids is essential for optimizing their application in advanced lubrication and thermal systems. In this study, GnP Nanofluids were synthesized using high oleic soybean oil as a biodegradable base fluid at varying GnP volume concentrations (0.025% to 2.15%) to investigate the percolation threshold and its impact on rheological performance. Particle stability was monitored via dynamic light scattering during synthesis, and morphological features were confirmed using scanning electron microscopy (SEM). Comprehensive rheological characterization, including temperature dependent viscoelasticity properties, shear stress-shear rate curves, and temperature ramping (25 - 80 °C), revealed a critical thermal transition around 50 °C. At this temperature, the nanofluids exhibited an abrupt rise in viscosity, signaling a change in microstructural dynamics strongly correlated with zeta potential behavior.

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.