New Coating Keeps Glass Clean and Fog-Free

Melinda Wenner

Date: 30 March 2007 Time: 06:37 AM ET

Jeffrey Youngblood, a Purdue assistant professor of materials engineering, works with equipment that enables researchers to measure the "contact angle" of a liquid as it beads up on a surface.
CREDIT: David Umberger

Foggy windshields and dirty sunglasses could soon be things of the past, thanks to a new glass coating developed by scientists at Purdue University.?

The property of glass that makes smudges difficult to remove is the same one that causes it to fog easily--a fatal attraction to grease. Oils stick more strongly to glass than water, and when water ends up on a pair of ski goggles that haven't recently been cleaned, it tends to bead up on the oil that's stuck to the glasses.

These water droplets then scatter light, creating a foggy appearance.

What if...

If glass were coated with something that made it attract water more strongly than oil, however, then both of these annoying problems could be solved, realized Jeffrey Youngblood, an associate professor of materials engineering at Purdue.

So Youngblood and postgraduate student John Howarter went to work, eventually developing a coating made of two layers. The bottom layer, consisting of a water-loving solvent called polyethylene glycol, pulls water in. The top surface contains a Teflon-like molecule that is large enough to prevent oil from passing through. The net result is that water coats the surface, forming a smooth thin layer rather than beading up, and oil is repelled--no smudges, no fog.

Most of the testing was done on glass surfaces, but Youngblood said preliminary studies show it should work on plastic lenses, too.

"Anybody who's gone [snow] skiing could realize the potential importance of being able to do that," said Kent Kirshenbaum, a chemist at New York University who was not involved in the research.

Self-cleaning, too

The coating has another major plus, too--it is self-cleaning.

"You add water, and the oil just comes right off," Youngblood told LiveScience. When water is added to the surface, it is pulled to the bottom layer, literally moving underneath the oil and displacing it.

In addition to windshields, mirrors, and eyeglasses, the coating could also be used in water filters, Youngblood said, because the coating allows water, but not oil, to pass through. His experiments have shown that filters treated with the coating remove 95 percent of oily contaminants, compared to only 5 percent in untreated filters.

Although it may be four or five years before a product ends up on store shelves, Youngblood envisions that when it does, it will be in the form of a solution that could be sprayed onto bathroom mirrors and sunglasses every couple of weeks to keep them clean and fog-free.