New Generation of Glass Coatings

Researchers at different locations have introduced a new generation of glass coatings that have some superb properties and numerous applications. It’s not surprising there is research in this area as organic polymer matrices decay over time when subjected to UV light and weathering.  In addition, the recent emphasis on energy efficiency and “cool roofs” has focused research on ways of lowering substrate temperatures and reflecting sunlight.

Workers at the DOE Oak Ridge National Laboratories have introduced a superhydrophobic anti-reflective glass coating that was inspired by the lotus leaf and the eye of the moth. We know that a lot of past coatings research has modeled after the lotus leaf in water repellency and thus self-cleaning properties.  But I did not know that a moth’s eyes are antireflective because of “naturally covered tapered nanostructures where the refractive index gradually increases as light travels to the moth’s cornea.”

Tolga Aytug, a member of ORNL’s Materials Chemistry Group, said “Combined, these features provide truly game-changing ability to design coatings for specific properties and performance.”

The nanostructured glass coatings have a surface that is a porous three-dimensional network of high-silica-content glass resembling microscopic coral. This unique structure suppresses reflected light which adds a benefit for use on solar panels.

“The unique three-dimensionality interconnected nanoporous nature of our coatings significantly suppresses Fresnel light reflections from glass surfaces, providing enhanced transmission over a wide range of wavelengths and angles,” Aytug said. The Fresnel effect describes the amount of light that is reflected versus the amount transmitted.  For solar panels, “the suppression of reflected light translates into a 3-6% relative increase in light-to-electricity conversion efficiency and power output of the cells. Coupled with the superhydrophobic self-cleaning ability, this could also substantially reduce maintenance and operating costs of solar panels.”

Because these coatings have superior mechanical resistance to impact abrasion, are thermal stable, and are effective at blocking UV light, they have a wide variety of applications from solar panels, optical instruments, etc., to impeding marine biofouling.

Meanwhile, scientists at the Johns Hopkins University Applied Physics Lab have developed a new, environmentally friendly paint made from glass that reflects sunlight off metal surfaces thus keeping them cool and durable.

“Most paints you use on your car or house are based on polymers, which degrade in the ultraviolet light rays of the sun,” says Jason J. Benkoski, Ph.D. “So over time you’ll have chalking and yellowing. Polymers also tend to give off volatile organic compounds, which can harm the environment. That’s why I wanted to move away from traditional polymer coatings to inorganic glass ones.”

Despite some ideal properties of glass such as its durability and optical properties, it is very brittle. Benkoski modified a version of potassium silicate such that, when sprayed out, is water resistant and is designed to expand and contract without cracking when applied on metal surfaces. By mixing in pigments the coating reflects sunlight so substrate surfaces remain at ambient temperature.

Funding for this work has come from the U.S. Department of Naval Research and the paints are intended for naval ships.  However there are many commercial applications for this type of paint.  Field testing is still to be conducted, but work done thus far is promising.  

This work was presented in a paper at the recent 250th National Meeting & Exposition of the American Chemical Society.

There are some nice new applications in coatings research these days that are proving to be cost effective and meet the new challenging environmental demands.  Let us know of other applictions!

Darlene