Scientists solve an 80-year-old physics mystery
Contact electrification (CE) was the earliest and only source of electricity for mankind until about the 18th century, but its true nature remains a mystery. Today, it is considered an essential part of technologies such as laser printers, LCD manufacturing processes, electrostatic painting, plastic separation for recycling and more, as well as a major industrial hazard (damage to electronic systems, explosions in coal mines, fires in chemical plants) due to its electrostatic discharges. (ESD) associated with CE. A 2008 study published in Nature found that ESDs from a simple adhesive tape in a vacuum are so powerful that they generate enough X-rays to make an X-ray of a finger.
It has long been believed that two contacting/sliding materials 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 experimentability, inherent inhomogeneities of contact materials or the general “stochastic nature” of CE.
A research team, led by Professor Bartosz A. Grzybowski (Department of Chemistry) of the Center for Soft and Living Matter, within the Institute for Basic Science (IBS) of Ulsan National Institute of Science and Technology (UNIST) has been investigating the possible sources of charge mosaics for more than a decade. The study is expected to help control potentially harmful electrostatic discharges and was recently published in the journal
In the paper published recently in Nature Physics, the group of Professor Grzybowski shows that charge mosaics are a direct consequence of ESD. The experiments demonstrate that between delaminating materials the sequences of “sparks” are created and they are responsible for forming the (+/-) charge distributions that are symmetrical on both materials.
“You might think that a discharge can only bring charges to zero, but it actually can locally invert them. It is connected with the fact that it is much easier to ignite the ‘spark’ than to extinguish it,” says Dr. Yaroslav Sobolev, the lead author of the paper. “Even when the charges are reduced to zero, the spark keeps going powered by the field of adjacent regions untouched by this spark.”
The proposed theory explains why charge mosaics were seen 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. It also hints at the origin of the crackling noise when you peel off a sticky tape – it might be a manifestation of the plasma discharges plucking the tape like a guitar string. Presented research should help control the potentially harmful electrostatic discharges and bring us closer to a true understanding of the nature of contact electrification, noted the research team.
References: “Charge mosaics on contact-electrified dielectrics result from polarity-inverting discharges” by Yaroslav I. Sobolev, Witold Adamkiewicz, Marta Siek and Bartosz A. Grzybowski, 8 September 2022, Nature Physics.
“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, 23 October 2008, Nature.
“The mosaic of surface charge in contact electrification” by H. T. Baytekin, A. Z. Patashinski, M. Branicki, B. Baytekin, S. Soh and B. A. Grzybowski, 23 June 2011, Science.
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