Scientists solve an 80-year-old physical mystery

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The study demonstrated that charge mosaics are a direct consequence of ESD.

Contact electrification (CE) was mankind’s first and only source of electricity until around the 18th century, but its true nature remains a mystery. Today, it is considered a critical component of technologies such as laser printers, LCD production processes, electrostatic painting, separation of plastics for recycling, etc., as well as a major industrial risk (damage to electronic systems, explosions in coal mines, fires in chemical plants) due to the electrostatic discharge (ESD) that accompanies CE. A 2008 study published in Nature found that in a vacuum, electrostatic discharges from a simple adhesive tape are so powerful that they generate enough X-rays to take an X-ray image of a finger.

For a long time it was believed that two materials in contact/sliding charge in opposite and uniform directions. However, after CE, it was discovered that each of the separated surfaces carries both (+) and (-) charges. The formation of so-called charge mosaics has been attributed to the irreproducibility of the experiment, the inherent inhomogeneities of the contacting materials, or the general “stochastic nature” of CE.

Professor Bartosz A. Grzybowski

Professor Bartosz A. Grzybowski. Credit: UNIST

A research team, led by Professor Bartosz A. Grzybowski (Department of Chemistry) of the Center for Soft and Living Matter, within the Institute of Basic Sciences (IBS) of the National Institute of Science and Technology of Ulsan (UNIST) has been investigating possible sources of charge mosaics for over a decade. The study is expected to help control potentially harmful electrostatic discharge and was recently published in the journal Natural Physics.

“In our 2011 Science paper, we showed a charge non-uniformity at the submicron scale of unknown origin. At that time, our hypothesis was to attribute these mosaics (+/-) to the transfer of microscopic plates of material between the separated surfaces. However, after many years of working on the problem, this model and related models simply didn’t hold up, as it gradually became difficult for us (and many other colleagues we’ve discussed) how these microscopic patches can explain even millimeter-scale regions. of opposite polarity coexisting on the same surface. Nevertheless, we and the community had no better answer as to why mosaics (+/-) are seen at all and on so many length scales,” says Professor Grzybowski.

Load mosaics on contact-loaded dielectrics

Figure 1. Charge mosaics on contact charged dielectrics. (a) In a conventional view, two electrically neutral materials (gray) are brought into contact and then uniformly separated (bottom left), one positive (red) and one negative (blue). In an alternative scenario (bottom right), each surface develops a highly non-uniform “charge mosaic” with neighboring domains of opposite charge polarities. (b) Collage of charge mosaics reported in the literature (years and scale bars are indicated). Credit: UNIST

In the article recently published in Natural Physics, Professor Grzybowski’s group shows that charge mosaics are a direct consequence of ESD. The experiments demonstrate that between the delaminating materials, sequences of “sparks” are created and that they are responsible for the formation of the symmetric (+/-) charge distributions on the two materials.

“You might think that a discharge can only bring the charges back to zero, but it can actually reverse them locally. This is related to the fact that it is much easier to ignite the “spark” than to extinguish it,” explains Dr. Yaroslav Sobolev, the main author of the article. “Even when the charges are reduced to zero, the spark continues to be field-fed from adjacent regions untouched by that spark.”

The proposed theory explains why charge mosaics have been observed on many different materials, including sheets of paper, rubbing balloons, steel balls rolling on Teflon surfaces, or polymers detached from the same or other polymers. polymers. It also indicates the origin of the crackling noise when you peel off an adhesive tape – this could be a manifestation of the plasma discharges by plucking the tape like a guitar string. The research presented should help control potentially harmful electrostatic discharges and bring us closer to a true understanding of the nature of contact electrification, the research team noted.

References: “Charge Mosaics on Contact Electrified Dielectrics Result from Reverse Polarity Discharges” by Yaroslav I. Sobolev, Witold Adamkiewicz, Marta Siek, and Bartosz A. Grzybowski, September 8, 2022, Natural Physics.
DOI: 10.1038/s41567-022-01714-9

“Correlation between nanosecond X-ray flashes and stick-slip friction in peeling tape” by Carlos G. Camara, Juan V. Escobar, Jonathan R. Hird and Seth J. Putterman, October 23, 2008, Nature.
DOI: 10.1038/nature07378

“The mosaic of surface charge in contact electrification” by HT Baytekin, AZ Patashinski, M. Branicki, B. Baytekin, S. Soh and BA Grzybowski, June 23, 2011, Science.
DOI: 10.1126/science.1201512

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