Self-Cleaning Windows

Dirty, streaky windows may soon be a thing of the past if Dr. Alidad Amirfazli’s research catches on. The NSERC-funded University of Alberta engineer is designing so-called “superhydrophobic” surfaces that force water to bead up and run off instead of spreading out.

There are two ways to make surfaces more hydrophobic, according to Dr. Amirfazli. The first is by chemical means, with compounds such as polytetrafluoroethylene – a non-stick coating commonly used on kitchen utensils, bakeware and frying pans.

“Hydrophobicity is measured by the angle of contact of the liquid to the surface. At a contact angle of 110° for polytetrafluoroethylene, we’ve reached the limit of what we can produce by chemical means,” he says.

“To obtain superhydrophobic surfaces – where angles of contact exceed 150° – manipulating the surface’s texture is the way to go,” he says. “Adding microtextures to the surface traps air, which floats and repels the liquid.”

His lab’s discovery of a 165° superhydrophobic surface actually resulted from one of those lucky accidents that sometimes lead to great inventions. Ph.D. student Reza Mohamadi and Kerry Hennig, a WISEST (Women in Scholarship, Engineering, Science and Technology) high school student, were using polymers to try to produce superhydrophobic surfaces, without success.

“Some of the polymer accidentally ended up on a metallic surface,” Dr. Amirfazli explains. “As the melt came into contact with the cold surface, it produced the right type of microtexture!”

Using lithography techniques, Dr. Amirfazli and his research team then artificially replicated the polymer surface on other materials.

“The technique should allow us to create superhydrophobic surfaces relatively inexpensively,” he says. “The challenge moving forward is to apply it to a variety of commercial materials, including glass.”

The research has already attracted interest from a U.S. high-tech company for use in material for semiconductor equipment.

“We think we’re really onto something,” Dr. Amirfazli says.

Contact:

Dr. Alidad Amirfazli
Tel.: (780) 492-6711
E-mail: a.amirfazli@ualberta.ca
Web site: http://www.mece.ualberta.ca/staff/alidad/