Breakthrough in ice-repelling materials

 

Icy weather is blamed for multibillion dollar losses every year in the United States, including delays and damage related to air travel, infrastructure and power generation and transmission facilities. Finding effective, durable and environmentally stable de-icing materials has been stymied by the stubborn tenacity with which ice adheres to the materials on which it forms.

Researchers from the University of Houston have reported a new theory in physics called stress localization, which they used to tune and predict the properties of new materials. Based on those predictions, the researchers reported in Materials Horizons that they have created a durable silicone polymer coating capable of repelling ice from any surface.

"We have developed a new physical concept and the corresponding icephobic material that shows extremely low ice adhesion while having long-term mechanical, chemical and environmental durability," they wrote.

Hadi Ghasemi, Bill D. Cook Assistant Professor of mechanical engineering at UH and corresponding author for the work, said the findings suggest a way to take trial and error out of the search for new materials, in keeping with the movement of materials science toward a physics-driven approach.

"You put in the properties you want, and the principle will tell you what material you need to synthesize," he said, noting that the concept can also be used to predict materials with superb antibacterial or other desirable properties.

His collaborators on the project include Payman Irajizad, Abdullah Al-Bayati, Bahareh Eslami, Taha Shafquat, Masoumeh Nazari, Parham Jafari, Varun Kashyap and Ali Masoudi, all with the UH Department of Mechanical Engineering, and Daniel Araya, a former UH faculty member who is now at the Johns Hopkins University Applied Physics Laboratory.

Ghasemi previously has reported developing several new icephobic materials, but he said those, like other existing materials, haven't been able to completely overcome the problem of ice adhering to the surface, along with issues of mechanical and environmental durability. The new understanding of stress localization allows the new material to avoid that, he said.

The new material uses elastic energy localization where ice meets the material, triggering cracks at the interface that slough off the ice. Ghasemi said it requires minimal force to cause the cracks; the flow of air over the surface of an airplane acts as a trigger, for example.

The material, which is applied as a spray, can be used on any surface, and Ghasemi said testing showed it is not only mechanically durable and unaffected by ultraviolet rays -- important for aircraft which face constant sun exposure -- but also does not change the aircraft's aerodynamic performance. Testing indicates it will last for more than 10 years, with no need to reapply, he said.

Novel materials convert visible into infrared light

 

Columbia University scientists, in collaboration with researchers from Harvard, have succeeded in developing a chemical process to convert visible light into infrared energy, allowing innocuous radiation to penetrate living tissue and other materials without the damage caused by high-intensity light exposure.

Their research is published in the January 17 issue of Nature.

"The findings are exciting because we were able to perform a series of complex chemical transformations that usually require high-energy, visible light using a noninvasive, infrared light source," said Tomislav Rovis, professor of chemistry at Columbia and co-author of the study. "One can imagine many potential applications where barriers are in the way to controlling matter. For example, the research holds promise for enhancing the reach and effectiveness of photodynamic therapy, whose full potential for managing cancer has yet to be realized."

The team, which includes Luis M. Campos, associate professor of chemistry at Columbia, and Daniel M. Congreve of the Rowland Institute at Harvard, carried out a series of experiments using small quantities of a novel compound that, when stimulated by light, can mediate the transfer of electrons between molecules that otherwise would react more slowly or not at all.

Their approach, known as triplet fusion upconversion, involves a chain of processes that essentially fuses two infrared photons into a single visible light photon. Most technologies only capture visible light, meaning the rest of the solar spectrum goes to waste. Triplet fusion upconversion can harvest low-energy infrared light and convert it to light that is then absorbed by the solar panels. Visible light is also easily reflected by many surfaces, whereas infrared light has longer wavelengths that can penetrate dense materials.

"With this technology, we were able to fine-tune infrared light to the necessary, longer wavelengths that allowed us to noninvasively pass through a wide range of barriers, such as paper, plastic molds, blood and tissue," Campos said. The researchers even pulsed light through two strips of bacon wrapped around a flask

Scientists have long tried to solve the problem of how to get visible light to penetrate skin and blood without damaging internal organs or healthy tissue. Photodynamic therapy (PDT), used to treat some cancers, employs a special drug, called a photosensitizer, that is triggered by light to produce a highly reactive form of oxygen that is able to kill or inhibit the growth of cancer cells.

Current photodynamic therapy is limited to the treatment of localized or surface cancers. "This new technology could bring PDT into areas of the body that were previously inaccessible," Rovis said.

"Rather than poisoning the entire body with a drug that causes the death of malignant cells and healthy cells, a nontoxic drug combined with infrared light could selectively target the tumor site and irradiate cancer cells."

The technology could have far-reaching impact. Infrared light therapy may be instrumental in treating a number of diseases and conditions, including traumatic brain injury, damaged nerves and spinal cords, hearing loss, as well as cancer.

Other potential applications include remote management of chemical storage solar power production and data storage, drug development, sensors, food safety methods, moldable bone-mimic composites and processing microelectronic components.

The researchers are currently testing photon-upconversion technologies in additional biological systems. "This opens up unprecedented opportunities to change the way light interacts with living organisms," Campos said. "In fact, right now we are employing upconversion techniques for tissue engineering and drug delivery."

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