Crank up voltage. Watch plastics crack

DUKE (US) — Engineers have documented how polymers—commonly found in wire insulation—breakdown when subjected to ever-increasing electric voltage.

Researchers have known for decades that polymers, such those insulating wires, may break down due to deformation of the polymers. But the process had never been seen at the microscopic level. The findings by the Duke University engineers could help in developing new materials to improve the durability and efficiency of any polymer that must come into contact with electrical currents, as well as in the emerging field of energy harvesting.

“We have long known that these polymers will eventually break down, or fail, when subjected to an increasing electrical voltage,” says Xuanhe Zhao, assistant professor of mechanical engineering and materials science. “Now we can actually watch the process as it happens in real time.”
httpv://www.youtube.com/watch?v=Ad-GJnxhaXc

Zhao is the senior scientist in the series of experiments performed by a graduate student Qiming Wang and published online in the Physical Review Letters.

The team attached the soft polymer to another rigid polymer layer, or protective substrate, which enabled observation of the deformation process without incurring the breakdown. They then subjected this polymer-substrate unit to various electrical voltages and observed the effects under a microscope.

“As bread dough rises in a bowl, the top surface of the dough may fold in upon itself to form creases due to compressive stresses developing in the dough,” Zhao says, “Surprisingly, this phenomenon may be related to failures of electrical polymers that are widely used in energy-related applications.”

“When the voltage reached a critical point, the compressive stress induced a pattern of creases, or folds, on the polymer,” says Zhao. “If the voltage is increased further, the creases evolved into craters or divots in the polymer as the electrical stress pulls the creases open. Polymers usually break down electrically immediately after the creasing, which can cause failures of insulating cables and organic capacitors.”

The substrate the researchers developed for the experiments not only allowed for the visualization of the creasing-to-cratering phenomenon, it could also be the foundation of a new approach to improving the ability of wires to carry electricity.

The research was supported by startup funds from Pratt.

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