Macroscopic superlubricity achieved by the synergic effect of silver nanoparticles and hexagonal boron nitride nanosheets

Superlubricity is a lubrication state with a coefficient of friction of less than 0.01, enabling efficient and stable mechanical operation under near-zero wear conditions. Although 2D nanomaterials have been tried to be used as additives in liquid lubricants to obtain the superlubricity, they tend to undergo a long break-in period accompanied by intense wear before reaching superlubricity, resulting in low load-bearing pressure. Therefore, the challenge of low load bearing pressure of 2D nanomaterials needs to be addressed in order to achieve long service life of the friction pair.

A team of lubrication scientists led by Jinjin Li from Tsinghua University in Beijing, China recently based on the synergistic effect of silver (Ag) nanoparticles and hexagonal boron nitride (hBN) nanosheets, a superlubricity state with high load-bearing pressure was achieved. The Ag nanoparticles were introduced on the surface of hBN sheets using dopamine as a linker. Further, the silver-modified hBN nanosheets (hBN-Ag) were used as additives to the aqueous ethylene glycol solution. The results showed that a superlubricity condition with a minimum coefficient of friction about 0.004 was achieved without a break-in period at a maximum contact pressure of 1.20 GPa. The achievement of superlubricity was attributed to the synergistic effect of Ag nanoparticles and hBN nanosheets, in which Ag nanoparticles were attached to hBN nanosheets to enhance the load-bearing capacity of hBN nanosheets. The Ag-modified hBN nanosheets produce extremely low friction and wear, contributing to the development of lubricants with high load bearing pressure and low wear rate.

The team published their paper in Nano Research on March 17, 2025.

In this work, Ag nanoparticles were deposited on the hBN surface through the reduction reaction of silver ions, revealing the synergistic superlubricity mechanism of hBN nanosheets and silver nanoparticles. Ag nanoparticles were tightly attached to hBN nanosheets and will not be detached from the surface during friction. The Ag-attached hBN nanosheets were more likely to be adsorbed and deposited on the friction interface, generating the tribofilm containing hBN-Ag nanosheets. The tribofilm reduced the direct contact of the friction pair and provided lower shear strength.

This work provides a new strategy for the achievement of superlubricity with hBN nanosheets under high load-bearing pressure by the modification of nanoparticles, contributes to the development of high-performance lubrication systems and opens up a new avenue for the application of 2D nanomaterials.

Other contributors include Yongfeng Yang, Rui Zhang, Shaowen Dong, and Xiaoyang Ma from the State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, China.

This work was supported by the National Key R&D Program of China (2020YFA0711003), National Natural Science Foundation of China (52175174, U2268212).

About the Authors

Dr. Jinjin Li is a full associate professor in the State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, China. His research interests focus on the mechanical surface lubrication theory, nano-additives and superlubricity technology. He has published over 100 research papers in prestigious international journals and received more than 20 Chinese national invention patents in recent years. For more information, please pay attention to his research homepage https://www.me.tsinghua.edu.cn/info/1095/2367.htm

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 17 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 2023 InCites Journal Citation Reports, its 2023 IF is 9.6 (9.0, 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.