Scientists at Duke University have observed for the first time how water droplets or air bubbles within polymers behave when they are touched by high electric voltages, and the knowledge gained from those observations may help us make better electrical grids or even optical systems.
“The effects of electric voltage on droplets in air or in liquid have been studied over decades,” says Xuanhe Zhao, assistant professor of mechanical engineering and materials science at Duke’s Pratt School of Engineering. “We take advantage of the understanding of these electrified drops in air or liquid every day, such as in the use of ink-jet printers. Conversely, no one has actually observed the effects of electric voltages on droplets in solids.”
When the researchers touched increasingly higher voltages to rubber or insulation for electrical power lines, they saw that the droplets or air bubbles slowly morphed from their spherical shape to a more tubular shape. The change in the droplets caused extremely large deformations within the insulating polymer material.
Droplets are sometimes trapped in polymers as defects during their manufacturing process. The deformations cause the polymers to crack and fail, the researchers say, and that may be the major reason why these materials fail and cause blackouts.
Changes in electrified drops in solids have not been well studied, because it has been very difficult to observe the process as the solid would usually break down before droplet transformation could be captured. This limitation has not only hampered our understanding of electrified droplets, but has hindered the development of high-energy-density polymer capacitors and other devices.
Zhao set about trying to find new polymers that were designed to carry increasingly higher loads of electricity, reports Azom.com. His experiments involved the use of droplets encapsulated within different types of polymers. Using a special technique, Zhao’s group saw how droplets in its new polymers formed a sharp tip before morphing into a tubular shape when they were exposed to increased voltage. A summary of Zhao’s study was published in a paper in the journal Nature Communications.
“Our study suggests a new mechanism of failure of high-energy-density dielectric polymers,” Zhao says. “This should help in the development of such applications as new capacitors for power grids or electric vehicles and muscle-like transducers for soft robots and energy harvesting.”
The polymers deformed at different voltages before they failed. “It appears that it could be possible, just by varying voltages, to change the shape of a particular polymer,” Zhao says. “One of the new areas we are now looking into is creating lenses that can be custom-shaped and used in ophthalmic settings.”
Source: “Study Suggests New Mechanism of Failure of High-Energy-Density Dielectric Polymers,” Azom.com, 10/24/12
Image by public domain.
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.