Cold, But No Ice

On the surface, University of Pittsburgh engineering professor Di Gao’s research effort doesn’t look like much. Nanoscale particles usually don’t, at least not to the naked eye. But look closely and you’ll see a hairylooking surface coating that actually prevents water from freezing—an innovation that now looks like a whole lot of commercial opportunity.

Gao, an assistant professor and William Kepler Whiteford Faculty Fellow in the Swanson School of Engineering’s Department of Chemical and Petroleum Engineering, and his research team have been working for the past five years on nanoparticle-based coatings that not only will repel water but also will prevent supercooled water from icing when the water hits a solid surface coated with his material. Gao refers to his innovation as an “anti-icing” solution.

“It’s a tough problem to solve,” says the Chinese-born Gao, who earned his PhD in chemical engineering at the University of California, Berkeley, in 2004. “Supercool water ices instantly when in contact with a solid. Then, you either have to heat the substrate or, when the ice forms, scrape it or somehow remove it.”

The key to solving the problem, he says, is to somehow not provide water with the ability to nucleate.

“It needs a nucleus to start the icing process,” Gao says of the cold water.

Inspired by the likes of the surfaces of lotus leaves, butterfly wings, and insect legs, Gao and his team have developed a coating made up of nanoparticles that are smaller than 50 nanometers in size. One nanometer is 1/1,000,000 of a millimeter in size. He has received grants from the National Science Foundation and the Mascaro Center for Sustainable Innovation, among others, to conduct his research.

Through a powerful microscope, the coating looks like a thick, fibrous lawn, with tiny air pockets between each particle. When water hits the “super-hydrophobic” coating, he explains, most of it simply rolls off the particle surface without ever touching the actual surface of the substrate—and without nucleating. Thus, no ice forms.

“The key point is that the size of the fundamental particles has to be small enough” to repel the water droplets, Gao says.

Among the most promising commercial applications, Gao suggests, are, for example, coatings for giant windmills. Ice, he says, often forms on the blades and can create rotational imbalances, which then can damage the giant turbines inside. He also envisions a large market for electrical power line coatings as well as those for airplanes and oil drilling platforms in cold locations, among other surfaces. “There are so many applications for this coating,” Gao says. “We’re open to all kinds of possibilities. But I think the most promising application is for power lines.”

Gao says his work isn’t finished yet. The challenge ahead, he suggests, is to refine the “robustness” of his coatings.

“Everything has a life span,” he says of the coatings that his team is developing.

Gao says that his team so far has developed a proof of concept, but like any coating development effort, his team still has to solve problems, such as adhesion, the effects of ultraviolet light exposure, and other issues that will differ depending on the type of surface substrate that will be coated.

Meanwhile, he continues to maintain a rather diverse portfolio of coatings research. He also is working on the development of dye-sensitized solar cells using ordered titanium oxide nanotubes, and he’s working with a physician at UPMC to develop DNA-based biosensors for influenza and other viruses.

And this past summer, he gained some national renown in the media during the Gulf of Mexico oil spill crisis for his development of what he calls a “super-oleophobic,” or oil-repellent, and “superhydrophilic,” or water-attracting, filter that could separate oil from seawater. But he still has the greatest hopes for his anti-icing innovation and its many application possibilities. Gao’s goal: “We could set up a new company,” he says. “I’m excited, but I know that sometime I will have to choose between product development and research.”