Self-cleaning windows, no-fog glasses, and stain-free fabrics just came a step closer to reality. Researchers at Ohio State University have discovered a way to coat materials with a transparent layer of very well organized chemical structures that can attract or repel water or oil or conduct electricity.
In the 1980's, scientists used a new kind of microscope to look at individual atoms for the first time. Being able to see and manipulate things so tiny inspired them to build structures and machines at the same invisibly small scale-- on the scale of one one-thousandth the diameter of a human hair. Nanotechnology was born.
A team of OSU physicists and chemists works on nano-scale coatings. While the coatings are made of a common plastic-like polymer, the team discovered a new way to assemble the polymer that enhances its physical properties-- like repelling or attracting water. Arthur Epstein, a professor of chemistry and physics, led the team.
"Polymers are like strings of pearls," he said. "It's poly meaning many, mer meaning an object, so many objects strung together like having pearls on a chain."
In this case, the pearls are individual molecules, and the chains they form as they hook together are known as nanofibers. To get a coating of nanofibers on a surface, it simply has to be dunked in a solution of water containing the individual molecules. Under the right conditions, the polymer chains will assemble themselves and coat the surface. But Epstein said previous attempts to coat surfaces with nanofibers resulted in messy intertwined chemical structures, not a uniform coating. The breakthrough came when a student in Epstein's lab tried growing the coatings in a more watered down solution.
"Nan-Rong Chiou, a student and then a post doc with me a the time, developed in the laboratory with us how to grow these nanofibers so they don't grow as an intertwined nest but rather grow so that they look like sort of a turf or a grass, a nano-turf growing straight upward," Epstein said.
Depending on the chemical treatment, they can make the transparent nanoturf attract or repel water or oil, conduct electricity, or even unwind DNA molecules.
"By bringing together the combinations of structuring the surface on a nano-scale and controlling the chemistry of the fibers sticking upward-- whether they're water-loving, water-hating, positive charged, negative charged, not charged, we can introduce lots of combinations of properties of potential use," Epstein said.
Of course everyone is familiar with surfaces that attract or repel water. Waxed cars and rain-exed windshields come to mind. The chemicals used to build the nanofibers are also nothing new. But Epstein says it's the uniform structure that makes the difference. The nanoturfs attract or repel water more intensely than a disorderly version of the same chemistry. Yushan Yan, a professor of chemical engineering at the University of California Riverside, says the OSU method is not the only way to grow a nanoturf with extreme properties, but it's definitely the simplest and most versatile.
"The simplicity to put this film on any surface is very significant, and I'm sure that people will look at this and generate a lot of other ideas," Yan said.
He says he may be able to use the new method in his own efforts to make more efficient fuel cells. Epstein says it's hard to predict where the super-coatings will turn up in the future, and commercial applications depend on which companies are interested.
The OSU research is published in the current issue of the journal Nature Nanotechnology.