A research team led by Professor Yong-Hyun Kim from the Department of Physics found the governing principle of triboelectric charging — friction-driven electron transfer between materials. Though triboelectric charging is commonly seen in daily life, such as in the generation of static electricity to lightning, the fundamentals of this phenomenon were unknown until now. None of the previously suggested theories could be applied to all of the triboelectric effects observed.

Professor Kim’s team aimed to find a universal law that could explain the cause-and-effect of triboelectric charging. They found that the occurrence of the triboelectric charging effect could be attributed to friction, and thinking of friction as energy dissipation also allowed the law to be applied more generally. The understanding that charge transfer is caused by friction-driven heat generation at the interface between materials was uncovered by taking note of the phenomenon in frictional heat conduction that leads to temperature differences in the materials and an abrupt temperature change in the interface between materials. 

By solving the related heat conduction equation and electronic structure calculations, the research team was able to quantify the triboelectric series, which shows the tendency of materials to gain or lose electrons. The series was determined by the triboelectric factor, derived from the thermodynamic properties of the material including the Seebeck coefficient. The Seebeck coefficient measures the thermoelectric voltage generated in terms of the temperature difference over the material. The triboelectric series had an absolute zero where the Seebeck coefficient was zero, with different materials having either a positive or negative triboelectric factor as per its Seebeck coefficient.

The team also suggested a new quantity “K”, called “the triboelectric power”, which can predict the magnitude of the potential drop that can be caused by triboelectricity. It is dependent on the square root of time, suggesting that a longer friction time is preferred for triboelectric-based energy harvesting.

Professor Kim stated, “I was lucky to solve the conundrum of triboelectric charging because I was studying thermodynamic phenomena in the microscopic world using quantum mechanics, and I’m grateful to my students and colleagues who persevered for such a long time.”

The increased understanding of triboelectric charging can aid the development of triboelectric-based energy harvesting technology. It will also open the possibility of microscopic control of triboelectric charging in various real-life applications, for example in semiconductor industries, where they may cause unwanted problems.

A research team led by Professor Yong-Hyun Kim from the Department of Physics found the governing principle of triboelectric charging — friction-driven electron transfer between materials. Though triboelectric charging is commonly seen in daily life, such as in the generation of static electricity to lightning, the fundamentals of this phenomenon were unknown until now. None of the previously suggested theories could be applied to all of the triboelectric effects observed.

Professor Kim’s team aimed to find a universal law that could explain the cause-and-effect of triboelectric charging. They found that the occurreance of the triboelectric charging effect could be attributed to friction, and thinking of friction as energy dissipation also allowed the law to be applied more generally. The understanding that charge transfer is caused by friction-driven heat generation at the interface between materials was uncovered by taking note of the phenomenon in frictional heat conduction that leads to temperature differences in the materials and an abrupt temperature change in the interface between materials. 

By solving the related heat conduction equation and electronic structure calculations, the research team was able to quantify the triboelectric series, which shows the tendency of materials to gain or lose electrons. The series was determined by the triboelectric factor, derived from the thermodynamic properties of the material including the Seebeck coefficient. The Seebeck coefficient measures the thermoelectric voltage generated in terms of the temperature difference over the material. The triboelectric series had an absolute zero where the Seebeck coefficient was zero, with different materials having either a positive or negative triboelectric factor as per its Seebeck coefficient.

The team also suggested a new quantity “K”, called “the triboelectric power”, which can predict the magnitude of the potential drop that can be caused by triboelectricity. It is dependent on the square root of time, suggesting that a longer friction time is preferred for triboelectric-based energy harvesting.

Professor Kim stated, “I was lucky to solve the conundrum of triboelectric charging because I was studying thermodynamic phenomena in the microscopic world using quantum mechanics, and I’m grateful to my students and colleagues who persevered for such a long time.”

The increased understanding of triboelectric charging can aid the development of triboelectric-based energy harvesting technology. It will also open the possibility of microscopic control of triboelectric charging in various real-life applications, for example in semiconductor industries, where they may cause unwanted problems.