GRAPHENE DE-ICER ADDS A SKILL FOR MILDER WEATHER
"We've learned to make an ice-resistant material for milder conditions in which heating isn't even necessary, but having the option is useful," says James Tour. "What we now have is a very thin, robust coating that can keep large areas free of ice and snow in a wide range of conditions."
A graphene-based de-icer now melts ice from wings and wires when conditions get too cold and keeps ice from forming at all if the air is above 7 degrees Fahrenheit.
The tough film that forms when the de-icer is sprayed on a surface is made of atom-thin graphene nanoribbons that are conductive, so the material can also be heated with electricity to melt ice and snow in colder conditions.
The material can be spray-coated, making it suitable for large applications like aircraft, power lines, radar domes, and ships, according to researchers in the Rice University lab of chemist James Tour. The study appears in the journal ACS Applied Materials and Interfaces.
Scientists have modified their graphene-based de-icer to resist the formation of ice well below the freezing point and added superhydrophobic capabilities. (Credit: Tour group/Rice)
“We’ve learned to make an ice-resistant material for milder conditions in which heating isn’t even necessary, but having the option is useful,” Tour says. “What we now have is a very thin, robust coating that can keep large areas free of ice and snow in a wide range of conditions.”
Tour, lead authors Tuo Wang, a graduate student, and Yonghao Zheng, a postdoctoral researcher, and their colleagues tested the film on glass and plastic.
Materials are superhydrophobic if they have a water-contact angle larger than 150 degrees. The term refers to the angle at which the surface of the water meets the surface of the material. The greater the beading, the higher the angle. An angle of 0 degrees is basically a puddle, while a maximum angle of 180 degrees defines a sphere just touching the surface.
The new films use graphene nanoribbons modified with a fluorine compound to enhance their hydrophobicity. They found that nanoribbons modified with longer perfluorinated chains resulted in films with a higher contact angle, suggesting that the films are tunable for particular conditions, says Tour, chair in chemistry and professor of computer science and of materials science and nanoengineering.
Warming test surfaces to room temperature and cooling again had no effect on the film’s properties, he says.
The researchers discovered that below 7 degrees, water would condense within the structure’s pores, causing the surface to lose both its superhydrophobic and ice-phobic properties. At that point, applying at least 12 volts of electricity warmed them enough to retain its repellant properties.
Applying 40 volts to the film brought it to room temperature, even if the ambient temperature was 25 degrees below zero. Ice allowed to form at that temperature melted after 90 seconds of resistive heating.
The researchers found that while effective, the de-icing mode did not remove water completely, as some remained trapped in the pores between linked nanoribbon bundles. Adding a lubricant with a low melting point (minus 61 degrees F) to the film made the surface slippery, sped de-icing, and saved energy.
Coauthors of the paper are from the University of Cambridge and Rice. The Air Force Office of Scientific Research supported the research.