Virginia Tech scientists have discovered an advanced bioinspired coating which could be used to prevent frost formation on critical surfaces such as aircraft parts and windscreens.
The technique was inspired by the Namib Desert beetle which consists of a water repellent surface studded with bumps that attract water. The bumps enable the beetle to collect airborne water which subsequently flows through the water-repellant channels to the insect’s mouth.
The new technology uses photolithography to create chemical micro-patterns that control frost growth due to condensation.
Jonathan Boreyko, Assistant Professor of Biomedical Engineering and Mechanics, Virginia Tech, said that the researchers mimicked this ability to control the growth of dew-drops which enabled the creation of frost-proof surfaces.
Frost formation across a surface begins with just one frozen drop. Boreyko said that ice harvests water from drew drops causing ice bridges to propagate frost across the droplets on the surface. A single frozen droplet is enough to get the chain reaction started.
The researchers controlled the spacing of the condensation and successfully controlled the speed at which frost grew across the surfaces and even prevented frost completely.
“We made a single dry zone around a piece of ice,” Boreyko said.
“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.”
The researchers developed the beetle-inspired chemical pattern on a very small surface – about a centimeter but they believe that the technique can be scaled up to large surface areas with thirsty, hydrophilic patterns on top of a hydrophobic, water-repellant surface.
“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.”
Frost-free zones on surfaces have a variety of applications. They could be used to keep wind turbines and aircraft wings frost-free, eliminating the need for deicing with harsh chemicals. They could also be used to keep glass surfaces like windscreens free from frost, thus improving their durability.
Excerpts and image courtesy of The Engineer