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.
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
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
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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