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In the course of human history, contact electrification (CE) served as the first and only source of electricity up to around the 18th century; nevertheless, the nature of this phenomenon is still a mystery. Electrostatic discharges (ESD) are a major industrial hazard that are caused by CE. These discharges can cause damage to electronic systems, explosions in coal mines, fires in chemical plants, and other similar disasters. Today, CE is considered a core component of technologies such as laser printers, LCD production processes, electrostatic painting, separation of plastics for recycling, and other similar disasters. ESDs produced by a piece of ordinary adhesive tape in a vacuum are so powerful that they can produce enough X-rays to produce an X-ray image of a finger [Nature 455, 2008, 1089-1092].

For a very long time, people believed that two materials that contacted or slid against one another created a charge that was opposing and uniform. However, in the 1940s, it was discovered that each of the divided surfaces carries both (+) and (-) charges after CE. This discovery was made after CE. It was hypothesized that the inability to reliably reproduce experiments, the intrinsic inhomogeneities of the materials that came into contact with one another, or the “stochastic nature” of CE dis general led to the formation of charge mosaics.

Over the past decade and a half, a group of researchers at UNIST, headed by Professor Bartosz A. Grzybowski (Department of Chemistry) from the Center for Soft and Living Matter, which is housed within the Institute for Basic Science (IBS), has been looking into the various potential causes of charge mosaics. This study, which was published online and will be featured in the edition of Nature Physics that will be released in October 2022, is anticipated to contribute to the regulation of potentially dangerous electrostatic discharges.

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“Sub-micrometer-scale charge non-uniformity of undetermined origin was demonstrated in a work that we published in Science in 2011 (Science 333, 2011, pp. 308–312). When we first noticed these (+/-) mosaics, our working idea was that they were caused by the movement of minute fragments of material back and forth between the two surfaces that were being separated. However, after many years of working on the issue, it became increasingly unclear to us (and many other colleagues with whom we discussed it) how these microscopic patches can explain even millimeter-scale regions of opposite polarity coexisting on the same surface. This is because it was gradually becoming unclear how these microscopic patches can explain how opposite polarity regions can coexist on the same surface. Despite this, neither we nor the community had a better explanation for why (+/-) mosaics are observed at all and at such a wide range of length scales “says Professor Grzybowski.

In the research study that was just recently published in Nature Physics, Professor Grzybowski’s group demonstrates that charge mosaics are a direct result of electrostatic discharge (ESD). Experiments have shown that between materials that are delaminating, sequences of “sparks” are formed, and these “sparks” are responsible for the formation of (+/-) charge distributions that are symmetrical on both materials.

“A discharge can actually invert charges in a localized area, contrary to what you might believe about its exclusive function of bringing charges to zero. It has to do with the fact that it is a lot simpler to light the’spark’ than it is to put it out, and there is the connection “According to the paper’s primary author, Dr. Yaroslav Sobolev, this statement was made. “Even when the charges are reduced to zero, the spark remains running driven by the field of adjacent regions that have not been untouched by this spark,” the scientist explained.

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The proposed theory provides an explanation for why charge mosaics were observed on a wide variety of materials, such as individual sheets of paper, rubbing balloons, steel balls rolling on Teflon surfaces, or polymers detached from the same or other polymers. It may also be a manifestation of the plasma discharges plucking the tape like a guitar string, which could explain the crackling noise that occurs when you tear off a sticky tape. This was also hinted at by the previous point. The research team emphasized that the presented research should assist limit potentially dangerous electrostatic discharges and get us closer to a true understanding of the nature of contact electrification.

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