Contact

Contact: Nicole Casal Moore

Media Relations & Research News Director

Michigan Engineering

Communications & Marketing

(734) 647-7087

3214 SI-North

A new coating developed at the University of Michigan can repel virtually any liquid and could lead to breathable protective wear for soldiers and scientists, as well as stain-proof garments. In this demonstration, it repels coffee. Photo: Joseph Xu, Michigan Engineering Communications & Marketing.An uncoated tile of screen is wetted by liquids, but a treated piece remains dry. University of Michigan researchers have developed a "superomniphobic" surface that can repel virtually any liquid.  Photo: Joseph Xu, Michigan Engineering Communications and Marketing.ANN ARBOR – A nanoscale coating that’s at least 95 percent air repels the broadest range of liquids of any material in its class, causing them to bounce off the treated surface, according to the University of Michigan engineering researchers who developed it.

In addition to super stain-resistant clothes, the coating could lead to breathable garments to protect soldiers and scientists from chemicals and advanced waterproof paints that dramatically reduce drag on ships.

Droplets of solutions that would normally damage either your shirt or your skin recoil when they touch the new “superomniphobic surface.”

“Virtually any liquid you throw on it bounces right off without wetting it. For many of the other similar coatings, very low surface tension liquids such as oils, alcohols, organic acids, organic bases and solvents stick to them and they could start to diffuse through and that’s not what you want,” said Anish Tuteja, assistant professor of materials science and engineering, chemical engineering and macromolecular science and engineering. Tuteja is the corresponding author of a paper on the coating published in the current issue of the Journal of the American Chemical Society.

The researchers tested more than 100 liquids and found only two that were able to penetrate the coating. They were chlorofluorocarbons – chemicals used in refrigerators and air conditioners. In Tuteja’s lab, in a demonstration, the surface repelled coffee, soy sauce and vegetable oil, as well as toxic hydrochloric and sulfuric acids that could burn skin. Tuteja says it’s also resistant to gasoline and various alcohols.

To apply the coating, the researchers use a technique called electrospinning that uses an electric charge to create fine particles of solid from a liquid solution. So far, they’ve coated small tiles of screen and postage-stamp sized swaths of fabric.

The coating is a mixture of rubbery plastic particles of “polydimethylsiloxane,” or PDMS, and liquid-resisting nanoscale cubes developed by the Air Force that contain carbon, fluorine, silicon and oxygen. The material’s chemistry is important, but so is its texture. It hugs the pore structure of whatever surface it’s being applied to, and it also creates a finer web within those pores. This structure means that between 95 and 99 percent of the coating is actually air pockets, so any liquid that comes in contact with the coating is barely touching a solid surface.

Play Video

Liquids bounce off super-repellent surface

Wednesday, January 16, 2013 3:17 p.m.

Close

Anish Tuteja, assistant professor of materials science and engineering, chemical engineering and macromolecular science and engineering, discusses and demonstrates his work with the "superomniphobic" coating.

Anish Tuteja, assistant professor of materials science and engineering, chemical engineering and macromolecular science and engineering, discusses and demonstrates his work with the "superomniphobic" coating.

Because the liquid touches mere filaments of the solid surface, as opposed to a greater area, the developed coating can dramatically reduce the intermolecular forces that normally draw the two states of matter together. These Van der Waals interaction forces are kept at a minimum.

“Normally, when the two materials get close, they imbue a small positive or negative charge on each other, and as soon as the liquid comes in contact with the solid surface it will start to spread,” Tuteja said. “We’ve drastically reduced the interaction between the surface and the droplet.”

With almost no incentive to spread, the droplets stay intact, interacting only with molecules of themselves, maintaining a spherical shape, and literally bouncing off the coating.

One classification of liquid that this coating repels is the so-called non-Newtonian category, which includes shampoos, custards, blood, paints, clays and printer inks, for example. These are liquids that change their viscosity depending on the forces applied to them. They differ from the Newtonians, such as water and most other liquids, whose viscosity stays the same no matter the force applied. Viscosity is a measure of a liquid’s resistance to flow on the application of force,and it’s sometimes thought of as its thickness.

A high-speed camera captures a droplet resting on the surface of a new super-repellent surface developed at the University of Michigan. Photo: Joseph Xu, Michigan Engineering Communications & Marketing.

“No one’s ever demonstrated the bouncing of low surface tension non-Newtonian liquids,” Tuteja said.

The paper is titled “Superomniphobic Surfaces for Effective Chemical Shielding.” Doctoral student Shuaijun Pan and postdoctoral researcher Arun Kota, both in materials science and engineering, are the first authors of the paper. Also contributing is Joseph M. Mabry, in the rocket propulsion division of the Air Force Research Laboratory. The work is funded by the Air Force Office of Scientific Research.

About Michigan Engineering: The University of Michigan College of Engineering is one of the top engineering schools in the country. Eight academic departments are ranked in the nation's top 10 -- some twice for different programs. Its research budget is one of the largest of any public university. Its faculty and students are making a difference at the frontiers of fields as diverse as nanotechnology, sustainability, healthcare, national security and robotics. They are involved in spacecraft missions across the solar system, and have developed partnerships with automotive industry leaders to transform transportation. Its entrepreneurial culture encourages faculty and students alike to move their innovations beyond the laboratory and into the real world to benefit society. Its alumni base of more than 75,000 spans the globe.

blog comments powered by Disqus