Morphology-engineered TiO₂ nanocrystals via solvothermal synthesis for enhanced colloidal stability and lubrication performance

Titanium dioxide (TiO₂) nanocrystals have garnered significant interest in nanofluid research field due to their controllable morphology, eco-friendly nature, and superior lubrication properties. However, the long-term dispersion stability of TiO₂ nanocrystals remains a significant challenge. This study demonstrates that the morphology, {001} facet exposure, and consequent surface modifier adsorption density of TiO₂ nanocrystals are synergistically controlled by modulating the facet-specific adsorption of oleic acid (OA), oleylamine (OM), and dioleamide during solvothermal synthesis. This control mechanism directly governs both dispersion stability and interfacial lubrication behavior. Crucially, the high-density modifier layer establishes a steric stabilization barrier, which ensures colloidal stability. The optimized TiO₂ nanocrystals (TiO₂-OAOM) exhibit colloidal stability for over 5 months and enhance the anti-wear properties of the base oil by 10-fold. Furthermore, synergistic interactions between TiO₂-OAOM and zinc dialkyl dithiophosphate (ZDDP) are confirmed in multiple friction pairs. These interactions promote the hardness and wear resistance of the tribo-film, thereby improving lubrication performance and suppressing metal transfer. This study provides a novel strategy for the co-optimization of dispersion stability and tribological properties of nanocrystals through surface engineering, offering novel insights into the design of nanofluids and a potent solution for lubrication challenges on low-hardness metals.