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Summary Sentence: Join Materials Science and Engineering as they present Dr. Zhong Lin Wang from Georgia Institute of Technology.
Full Summary: No summary paragraph submitted.
Zhong Lin Wang
Abstract:
Although contact electrification (triboelecrification) (CE) has been documented since 2600 years ago, its scientific understanding remains inconclusive, unclear and un-unified. This paper reviews the updated progress for studying the fundamental mechanism of CE using Kelvin probe force microscopy for solid-solid cases. Our conclusion is that electron transfer is the dominant mechanism for CE between solid-solid pairs. Electron transfer occurs only when the interatomic distance between the two materials is shorter than the normal bonding length (typically ~0.2 nm) in the region of repulsive forces. A strong electron cloud overlap (or wave function overlap) between the two atoms/molecules in the repulsive region leads to electron transition between the atoms/molecules, owing to the reduced interatomic potential barrier. The role played by contact/friction force is to induce strong overlap between the electron clouds (or wave function in physics, bonding in chemistry). The electrostatic charges on the surfaces can be released from the surface by electron thermionic emission and/or photon excitation, so these electrostatic charges may not remain on the surface if sample temperature is higher than ~300-400 0C.
The electron transfer model could be extended to liquid-solid, liquid-gas and even liquid-liquid cases. As for the liquid-solid case, molecules in the liquid would have electron cloud overlap with the atoms on the solid surface at the very first contact with a virginal solid surface, and electron transfer is required in order to create the first layer of electrostatic charges on the solid surface. This step only occurs for the very first contact of the liquid with the solid. Then, ion transfer is the second step and is the dominant process thereafter, which is a redistribution of the ions in solution considering electrostatic interactions with the charged solid surface. This is proposed as a two-step formation process of the electric double layer (EDL) at the liquid-solid interface.
The fundamental theory of the triboelectric nanogenerators (TENGs) is explored based on a group of reformulated Maxwell equations. In the Maxwell’s displacement current proposed in 1861, the term e¶E/¶t gives the birth of electromagnetic wave, which is the foundation of wireless communication, radar and later the information technology. Our study indicates that, owing to the presence of surface polarization charges present on the surfaces of the dielectric media in TENG, an additional term ¶Ps/¶t that is due to non-electric field induced polarization should be added in the Maxwell’s displacement current, which is the output electric current of the TENG. From a set of reformulated Maxwell equations, we derived the first principle theory of TENG.
Biography:
Dr. Zhong Lin (Z.L.) Wang received his Ph.D in Physics from Arizona State University in 1987. He is the Hightower Chair in Materials Science and Engineering, Regents' Professor, and College of Engineering Distinguished Professor at the Georgia Institute of Technology. He served as a Visiting Lecturer in SUNY (1987-1988), Stony Brook, as a research fellow at the Cavendish Laboratory in Cambridge (England) (1988-1989), Oak Ridge National Laboratory (1989-1993) and at National Institute of Standards and Technology (1993-1995) before joining Georgia Tech in 1995. He is the Hightower Chair in Materials Science and Engineering and Regents' Professor at Georgia Tech. He is also the founding director and director of the Beijing Institute of Nanoenergy and Nanosystems.
