When a chair is pulled and produces a scraping sound, or when a machine tool vibrates, these phenomena are explained by an increase in frictional force known as the 'stick-slip phenomenon'. Jeonbuk National University (JBNU) Professor Sangmin Ahn (Department of Physics, College of Natural Science) and his research team have, for the first time, demonstrated that such phenomena can result from an increase in nanoscale surface friction caused by nanoscale water—water consisting of an extremely small number of molecules—and their finding has attracted attention from the academic community.

They showed that the principle of friction, the most commonly encountered and useful force in daily life, can be defined even by 'nanoscale water', which is invisible yet frequently present in natural phenomena.

The findings were published in the May issue of the leading nanoscience journal Nano Research (IF = 8.897). (Paper title: Capillary grip-induced stick-slip motion) Professor Je Won-ho of Seoul National University, Professor Lee Man-hee of Chungbuk National University, and Dr. Bong-su Kim of Samsung Advanced Institute of Technology participated in the collaborative research.

The origin of friction can be explained by the 'cold welding' phenomenon, in which contacted areas momentarily adhere due to compressive force. To separate these adhered regions, a certain threshold force (static friction) must be applied before movement occurs. While moving, the object continues to experience frictional force (kinetic friction). When the moving interface encounters a point where the adhered area increases, it stops again. This phenomenon is called stick-slip.

Until now, stick-slip was regarded as repeated action between static and kinetic friction at the contact points between two surfaces. However, this study confirmed that nanoscale water trapped between small contact regions can increase friction by exerting a vertical pull on the two surfaces, and that an increase in the amount of nanoscale water can induce previously unseen stick-slip behavior. The research team stated that they utilized a self-built atomic force microscope.

Professor Sangmin Ahn said, "We live in an era of rapidly growing scientific and industrial interest in nanoscale materials. An in-depth microscopic understanding of friction, which underlies fundamental material properties, will provide the momentum to surpass current limits in science and technology."

Meanwhile, the study was carried out through close collaboration between JBNU, Professor Je Won-ho of the Department of Physics and Astronomy at Seoul National University, and Professor Lee Man-hee of the Department of Physics at Chungbuk National University. It was supported by the Ministry of Science and ICT and conducted under the National Research Foundation of Korea's Leader Researcher Program, Creative Challenge Researcher Program, and Early-Career Research Program.

Paper link : https://link.springer.com/article/10.1007/s12274-022-4348-9