Morphology-engineered TiO2 nanocrystals achieve record colloidal stability and lubrication performance
image: TEM images show TiO2 nanocrystals with different shapes (from rods to quantum dots) synthesized via solvothermal methods. The quasi-spherical TiO2-OAOM sample (center) achieved over 5 months of colloidal stability and a 10-fold improvement in anti-wear performance.
Credit: Nano Research, Tsinghua University Press
Friction and wear are the ‘energy drains’ and ‘lifespan terminators’ in the mechanical world. Conventional lubricant additives, such as the well-known zinc dialkyldithiophosphate (ZDDP), are highly effective but contain environmentally harmful elements such as sulfur and phosphorus. Moreover, their lubrication performance is significantly poor on ‘soft metals’ such as aluminum alloys and stainless steel. Titanium dioxide (TiO2) nanocrystals, with their controllable morphology and eco-friendly properties, are considered as ideal candidates for the next-generation lubricant additives.
In a study published in Nano Research, a team from Shanghai Advanced Research Institute of Chinese Academy of Sciences (SARI, CAS), has designed TiO2 nanocrystals with precisely controlled morphologies that significantly enhance both colloidal stability and lubrication performance.
The team employed a solvothermal method to synthesize TiO2 nanocrystals with diverse morphologies, such as rods, spheres, rhombic shapes, and quantum dots. This was achieved by adjusting the ratio of oleic acid (OA) to oleylamine (OM) and selecting different solvents. Notably, quasi-spherical nanocrystals synthesized with a 6:4 ratio of OA to OM (termed TiO2-OAOM) showed the best lubrication performance. These nanocrystals remained uniformly dispersed in the base oil for over 150 days and demonstrated a remarkable reduction in wear volume by 90% and in the coefficient of friction by 47%.
A key finding was that the high-energy {001} crystal facets and small particle size promoted dense adsorption of surface modifiers, creating a steric barrier that prevented aggregation. This mechanism, rather than electrostatic repulsion, was identified as the main driver of colloidal stability.
Moreover, when combined with ZDDP, the TiO2-OAOM nanocrystals embedded into the tribo-film, increasing its hardness and elastic modulus by 53% and 11%, respectively. This composite film effectively reduced metal transfer and wear across multiple friction pairs, such as stainless steel and brass.
This work provides a practical pathway to co-optimize dispersion stability and tribological performance through crystal morphology control. It opens new possibilities for designing intelligent lubrication systems, especially for soft metals where conventional additives fall short.
This work was supported by Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB0470202), International Partnership Program of Chinese Academy of Sciences (No. 307GJHZ2022034GC), and Key Project of the Henan Province Science and Technology Research and Development Joint Funds (No. 235101610007).
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.