The earliest spark of electricity known to man was from contact electrification (CE)— when nearby surfaces become electrically charged.
Even today, it forms an important part of the technologies that operate laser printers, produce LCDs, and separate plastics for recycling. CE can also cause industrial hazards such as damage to electronic systems, explosions in coal mines or fires in chemical plants due to electrostatic discharge (ESD) which is accompanied by CE.
Previously, it was assumed that two materials in contact with each other or sliding against each other produce charges that are opposite and uniform.
However, after the 1940s, it was found that each surface carries a heterogeneous distribution of both positive and negative charges after contact, called a charge mosaic. Application of the theory of charge mosaics can be seen using many materials such as sheets of paper, balloons, and steel balls rubbed on Teflon surfaces.
Scientists have been trying to predict models and find the source of this heterogeneity for decades. It was previously assumed that the heterogeneity must be due to some innate physical property of the contact materials themselves.
Now, a study published in Nature Physics may have found the answer to this mystery.
“In our 2011 Science paper, we showed sub-micrometre-scale charge non-uniformity of unknown origin. At that time, our hypothesis was to attribute these (+/-) mosaics to the transfer of microscopic patches of materials between the surfaces being separated. However, over many years of work on the problem, this and related models were simply not holding up, as it was gradually becoming unclear to us (and many other colleagues with whom we discussed) how these microscopic patches can explain even millimetre-scale regions of opposite polarity coexisting on the same surface. Nonetheless, we and the community had no better answer why the (+/-) mosaics are seen at all and over so many length scales,” Professor Bartosz A. Grzybowski, one of the study’s authors, said in a release.
The research, conducted by a group of scientists led by Dr. Grzybowski at the Ulsan National Institute of Science & Technology, reveals that the charge mosaics are a direct consequence of electrostatic discharge (ESD) between separating surfaces.
The experiments conducted by the scientists showed that a series of phenomena that produce the ‘spark’ starts as the two surfaces grow apart. It also showed that the electrostatic discharge or the ‘spark’ is responsible for forming the charge distributions on both the 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,” he added.
According to the scientists, this research will help control harmful ESD and reveal the nature of contact electrification.
