Ice. It’s an annoying byproduct of life lived in many parts of the world. With much of the world still steeped in winter, ice continues to prove challenging, impacting a variety of surfaces from planes and roadways to solar panels.

Ice build-up on the wings of planes, for instance, destroys lift, increases drag and even threatens the safety of the airplane. Likewise, ice can cause delays and cancelled flights, thereby costing both time and money. The same holds true for icy roadways, which pose a threat to drivers. Meanwhile, ice buildup on solar panels can damage surfaces and impede energy production.

Following are a number of recent developments being implemented to create anti-icing or de-icing solutions affecting surfaces in the transportation and energy sectors. This first in a series of articles looks specifically at airplanes.

Laser ice repellent

Researchers from the Fraunhofer Institute for Material and Beam Technology, Airbus and the Dresden University of Technology are employing direct laser interference patterning (DLIP) technology to etch 3D microscale structures into aircraft wings to minimize the accumulation of ice.

The airfoil with the water-repellent structured surface. Source: Airbus

To accomplish this, the team uses short and ultrashort pulse lasers to develop surface structures, processing up to one sq m of material per minute. The fragmented surface finished product reportedly eliminates the adhesion points for ice.

De-ice coating

University of Illinois Chicago (UIC) researchers have developed a patent-pending de-icing coating that prevents ice accumulation on the surface of airplanes. The coating, according to its developers. is based on a recipe that includes current de-icing chemicals.

“We questioned the lifetime of the cryoprotectants and looked at new ways to increase their effectivity,” the researchers explained. “Glycols dissolve very fast in the water and get washed away before the plane takes off, and it’s a serious problem that costs hundreds of millions of dollars — most of which literally ends up in the drain. We thought, why not improve such chemicals themselves, and make alternatives that can last longer while being more biofriendly. And that is what we ended up doing.”

From this, the researchers developed a family of 80-plus anti-freezing coatings that can be applied to assorted surfaces including aluminum, glass, steel, copper, plastic or any industrial surface.

According to the company, the coating can delay the formation of frost on such surfaces for hours and can easily shed off any ice that does eventually accumulate thereafter.

Because the UIC coating lasts longer, the researchers suggest that its use on airplane wings could prevent the occurrence of chemical runoff, which pollutes freshwaters as happens with current de-icing chemicals. While these chemicals de-ice the wings, once the plane takes flight, the chemicals disperse, running off to the ground or water below it, thereby leaving the wings vulnerable to re-icing.

Aluminum pillars

Because ice once removed from an airplane wing can reform after takeoff, researchers from Virginia Polytechnic Institute and State University and the University of California have engineered a water-repellent surface to prevent this occurrence.

The newly engineered water-repellent surface uses aluminum millimeter-sized pillars instead of commonly used chemical solutions. According to the researchers, as frost forms on top of the aluminum pillars, tiny ice bridges are subsequently created, trapping pockets of air underneath. As such, the trapped air pockets suspend the ice sheet, reducing the amount of adhesion the ice has to the surface.

Source: Stephan HerbLeaf geometry

Researchers from Northwestern University have developed a method inspired by the geometry of leaves for preventing the formation of ice on surfaces such as airplane wings.

Recognizing that the convex features of leaves tend to invite more frost formation than the concave features, the researchers discovered that modifying the texture of surfaces was key to reducing frost formation, by a reported 60% according to the study.

Surfaces rippled with peaks and valleys, like a leaf, discourage the formation of frost, according to researchers, because condensation is encouraged on the leaf’s peaks and suppressed in its valleys. The fraction of condensed water that collects in the valleys, reportedly evaporates, according to the research. As such, those components are virtually frost free when the temperature drops below freezing.

To achieve the ideal geometry of peaks and valleys on a surface to discourage frost formation, the team found that surfaces with millimeter-sized peaks and valleys with angles in the 40° to 60° range worked best. While frost still formed on surface peaks during testing when temperatures fell below freezing, it was defrosted using far less energy than was previously required to defrost a surface without peaks and valleys.

Sprayable coating

Engineers at the University of Houston have developed a sprayable ice-shedding coating to prevent ice formation on airplane wings.

The team of University of Houston researchers call the coating a “fracture-controlled surface,” suggesting that it is 100 times stronger than all coatings currently in development and on the market.

Wing

The coating reportedly earned its name by employing various chemical and mechanical compositions to encourage crack formation at the interface, directing energy toward those cracks, and thus accelerating their growth.

"We developed a new concept in which, through material design, you can significantly accelerate the crack formation and growth and easily remove external objects from the surface. This concept is implemented to develop materials that are highly durable, and ice does not attach to these materials. Fracture-controlled surfaces provide a rich material platform to guide future innovation of materials with minimal adhesion while having very high durability," explained University of Houston researchers.

Successfully preventing the dangerous buildup of ice on airplane wings is due to the coating’s three phases — the matrix phase, the crack formation phase and the phase for guiding crack propagation.

According to the researchers, the coating relies on the principle that force needs to be applied to remove external solid objects from surfaces, thereby encouraging the development of cracks at the interface. As the cracks begin to form, they grow quickly, detaching the ice entirely from the surface.

Moth eyes

Researchers from Tan Trao University and Thai Nguyen University of Education in Vietnam have developed a transparent anti-icing nanostructure inspired by moth’s eyes.

Built on a quartz substrate, the nanostructure was cloaked in a layer of paraffin wax, which is both water repellent and demonstrates low thermal conductivity.

Ice accumulation on a bare coated, nanostructure (NS) and nanostructure covered in paraffin (NSP) samples after a freezing test. Source: Nguyen Ba Duc

During testing, the combination of the material’s ability to repel water and its heat-delayed construction made it possible to mimic the anti-icing characteristics of moth's eyes, interrupting the icing process during water droplet and freezing rain tests.

Likewise, the air blocks trapped within the nanostructure also delayed heat transfer, which increased the attached water droplets’ freezing times.

According to researchers, the material could have implications for aircraft wings, which when iced over could lead to tragic accidents.

Check back with GlobalSpec.com for more about our series on surface de-icing solutions. Next time we will investigate the solutions for de-icing roadways.