Korean Researchers First in the World to Identify the Order of Liquids Prone to Static Electricity

First Discovery of Triboelectric Series Enables Selection of Specific Liquids on Semiconductor Device Surfaces for Energy Harvesting Devices

Domestic researchers have unveiled another layer of the secret behind the electrostatic phenomenon (triboelectric charging) occurring in liquid substances for the first time in the world. Following the discovery in 2013 that electrostatic charges can occur in liquids, they have now identified the order in which electrostatic charges are more easily generated in different liquids. This can be applied to improving the efficiency of energy harvesting devices or selecting liquids for cleaning semiconductor device surfaces.

A research team in our country has identified for the first time the order in which electrostatic (triboelectric) charging occurs most effectively among liquids. Photo by Ministry of Science and ICT

The Ministry of Science and ICT announced that the research teams led by Professor Kim Dong-sung of Pohang University of Science and Technology and Professor Choi Dong-hwi of Kyung Hee University have established the triboelectric series for liquids for the first time worldwide. The triboelectric series refers to the arrangement of materials in order of their tendency to become positively charged when in contact with another material.

The research results were published as a cover paper in the international journal Advanced Materials the day before (local time).

The electrostatic phenomenon (triboelectric effect) refers to the occurrence of opposite electric charges on the surfaces of two objects when friction occurs between them. The triboelectric series is a sequence of materials arranged according to how easily this phenomenon occurs. Although electrostatic phenomena have been studied since ancient times, it is difficult to define them quantitatively, so the triboelectric series, which indicates the relative degree of triboelectric charging between objects, is the only method used to describe electrostatic phenomena.

The research team discovered that liquid droplets falling on silicone oil moved unexpectedly due to an unknown force while using a pipette, a device for transporting a precise amount of liquid, in the laboratory. Continuing research to explain this phenomenon, they reported the electrostatic phenomenon of liquids occurring during the pipetting process to the academic community for the first time in 2013.

Interest in electrostatic phenomena occurring not only between solids but also between solids and liquids has begun to grow. However, the existing triboelectric series was limited to solid materials, and no method existed to describe this phenomenon in liquids. The research team proposed a measurement method that controls various external factors such as frictional movement and contact area between a solid with a fixed charge and a liquid to precisely measure the electrostatic phenomenon of liquids and establish a triboelectric series for liquids.

Using this measurement method, they measured triboelectric charging for 22 types of liquids and classified them according to the degree of charging. This is the world's first result establishing the electrostatic phenomena of various liquids based on experimental data.

By using the triboelectric series for liquids established by the research team, it is possible to select liquids according to the intended purpose and control electrostatic phenomena. For example, it is expected to have high applicability in improving the efficiency of energy harvesting devices or selecting liquids for cleaning semiconductor device surfaces.

Professor Kim said, “This research achievement is the first case of establishing a triboelectric series for liquids based on the electrostatic properties of liquids,” and added, “Starting with this research result, it is expected that the triboelectric series for liquids will be expanded to include a wider variety of liquids.”

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