by Staff Writers
Cleveland OH (SPX) Aug 30, 2017
For centuries, scientists have tried to understand triboelectric charging, commonly known as static electricity.
Triboelectric charging causes toner from a photocopier or laser printer to stick to paper, and likely facilitated the formation of planets from space dust and the origin of life on earth.
But the charges can also be destructive, sparking deadly explosions of coal dust in mines and of sugar and flour dust at food-processing plants.
New research led by Case Western Reserve University indicates that tiny holes and cracks in a material - changes in the microstructure - can control how the material becomes electrically charged through friction.
The research is a step toward understanding and, ultimately, managing the charging process for specific uses and to increase safety, the researchers say. The study is published in the journal Physical Review Materials.
"Electrostatic charging can be seen everywhere, but we noticed some cases where materials appeared to charge more - like a balloon rubbed on your head, or packing peanuts sticking to your arm when you reach into a package," said Dan Lacks, chair of the Department of Chemical and Biomolecular Engineering and one of the study's lead authors.
"Our idea was that a strain on the materials was causing a higher propensity for the materials to become charged," Lacks said. "After blowing polystyrene to create the expanded polystyrene that comprises the peanut, the material maintains this distinct charging behavior indefinitely."
Testing the idea
"Triboelectric charging experiments are generally known for their - as some would say - charmingly inconsistent results," said Andrew Wang, a Case Western Reserve PhD student and co-author who led the work. "What was surprising to me, initially, was the consistency of the unstrained versus strained charging results."
Lacks, Wang and Mohan Sankaran, professor of chemical engineering and the other lead author of the study, repeatedly found a systematic charge transfer in one direction, as if the materials were made of two different chemical compositions.
After rubbing, unstrained films clearly tended to carry a negative charge and the strained film a positive charge. The finding was not consistent 100 percent of the time, but statistically significant.
In contrast, unstrained films rubbed together and strained films rubbed together appeared to charge at random.
Analyzing the results
The only detectable difference in the strained film from the unstrained film was the presence of voids in the material - holes and fractures created by stretching, which changed the microstructure. Some holes and fractures were detected with the naked eye, while others were so small they required the aid of a scanning electron microscope.
The researchers created molecular simulations of strained materials on a computer, which showed the birth of the voids but no other significant changes. That further indicated the change in microstructure is the likely cause of the systematic charge transfer.
"We think the void regions and the fibrils we see around them when we strain the polymer have different bonding and thus charge differently," Lacks said.
Although the experiment focused on one material, strain may affect all materials, Sankaran said. "The strain we put on the PTFE was large because we were looking for big effects," he said. "All materials may have a little strain from processing."
They hope to understand the scientific basis of triboelectric charging and then control the process. The goal: to prevent damage and explosions or exploit the charging for beneficial uses, such as charged agricultural pesticides that stick better to plants, or paints for cars or even spray tans. Better adhesion would reduce the amounts applied and wasted.
Beyond earthly uses, Wang said, these applications and mitigation strategies might be more pertinent in the coming years as manned and unmanned space missions deal with moon, Mars and asteroid dust.
Washington (UPI) Aug 29, 2017
Researchers in Australia have grown bendable crystals strong enough to be tied in knots. Scientists are now considering how the flexible single crystals can be incorporated in new technologies and commercial applications. "Crystals are something we work with a lot - they're typically grown in small blocks, are hard and brittle, and when struck or bent they crack or shatter," John McMur ... read more
Case Western Reserve University
Space Technology News - Applications and Research
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement|