Scientists have found why rubbing two materials, such as a balloon on hair causes static electricity to charge the materials and makes it stick.
Tiny holes and cracks in a material — changes in the microstructure — can control how the material becomes electrically charged through friction, showed the findings 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 one of the study’s lead authors Dan Lacks from Case Western Reserve University in Cleveland, Ohio, US.
“Our idea was that a strain on the materials was causing a higher propensity for the materials to become charged,” Lacks said.
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.
The new research, according to the researchers, is a step toward understanding and, ultimately, managing the charging process for specific uses and to increase safety.
To test the theory that strain affects charging, the researchers stretched a film of polytetrafluoroethlyne (PTFE) and rubbed it against a film of unstrained PTFE.
They 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.
In contrast, unstrained films rubbed together and strained films rubbed together appeared to charge at random.
Researchers used X-ray diffraction and Raman spectroscopy to analyze samples of strained and unstrained films and found at the atomic level, they looked nearly the same.
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.
The findings indicated that change in microstructure was the likely cause of the systematic charge transfer.