Cold winter mornings mean that our car ice scrapers start getting regular use. Freezing temperatures and morning dew create ice covered windshields that take some elbow grease to remove.
While scraping our windshields is a nuisance, a buildup of ice on an aircraft can actually be quite dangerous. Airplanes are sprayed with harsh chemicals to remove ice and, in flight, warm engine air can be rerouted to keep wings from accumulating ice.
When ice accumulates on wind turbine blades, they become far less efficient. Deicing measures have to be taken regularly to allow them to generate an optimum amount of energy.
Researchers at Virginia Tech have come up with a solution that would prevent ice from forming on these types of surfaces so that those harsh chemicals and labor intensive practices can be done away with.
The Namib Desert Beetle is one of those organisms that manages to thrive in an extreme environment. It lives in one of the hottest places of the world, but is able to collect airborne water to survive. The Virginia Tech researchers found that a material mimicking the shell of the beetle kept moisture and ice from forming on the surface.
The beetle has a bumpy shell where the tips of the bumps attract moisture to form drops and the sides are smooth and repel water. That creates channels that lead directly to the beetle’s mouth. This bumpy design made researchers realize that they could control where dew drops grew.
The scientists developed a patterned surface by using photolithography to create chemical arrays that attract water over top of a surface that repels water to control the spread of ice. They believe the material can be scaled-up to large surface areas like airplane wings and wind turbine blades and also heat coils and car windshields.
"We made a single dry zone around a piece of ice," says Jonathan Boreyko, assistant professor of Biomedical Engineering and Mechanics at Virginia Tech. "Dew drops preferentially grow on the array of hydrophilic dots. When the dots are spaced far enough apart and one of the drops freezes into ice, the ice is no longer able to spread frost to the neighboring drops because they are too far away. Instead, the drops actually evaporate completely, creating a dry zone around the ice."
A single frozen dew drop can start the spread of ice because ice harvests water from dew drops and ice bridges begin forming, creating a chain reaction. The pattern keeps dew drops separated, which keeps this chain reaction from happening.
“Fluids go from high pressure to low pressure,” Boreyko said. “Ice serves as a humidity sink because the vapor pressure of ice is lower than the vapor pressure of water. The pressure difference causes ice to grow, but designed properly with this beetle-inspired pattern, this same effect creates a dry zone rather than frost.”
Because keeping surfaces dry and ice-free is energy intensive, this breakthrough could save time, money and energy in a variety of applications.