Anish Tuteja’s work could have wide commercial use, including on clothes and ships.
Bureau Report
NEW YORK: An Indian American professor at the University of Michigan, Anish Tuteja, has developed a chemical coating that repels the broadest range of liquids of any material in its class, causing them to bounce off the treated surface, and is likely to be developed for use in a wide variety of daily use, from clothes to ships.
In addition to super stain-resistant clothes, the nanoscale coating that’s at least 95 percent air and termed ‘superomniphobic’ surface, could lead to breathable garments to protect soldiers and scientists from chemicals, and advanced waterproof paints that dramatically reduce drag on ships, reported Phys.org. Tuteja is the corresponding author of a paper on the coating published in the current issue of the Journal of the American Chemical Society.
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, at the University of Michigan.
Tuteja and his colleagues 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, said the report.
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, said Phys.org.
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.
“No one’s ever demonstrated the bouncing of low surface tension non-Newtonian liquids,” Tuteja said.
Tuteja and his colleagues have been working on similar omniphobic surfaces for over five years, but this one is the best by far, he told NBC News.
“On the first generations, the droplets were leaving something behind,” he said — a problem around hazardous materials that could cause trouble later by evaporating or falling off. Not any more,” he told NBC.
The work’s not done, Tuteja said. Although he has “three or four” parties interested in this type of material, not least of which is the military (which partially funded the research), there are still improvements to be made, said NBC.
Tuteja has a B.E. Chemical Engineering, Panjab University (India), 2001, did his Ph.D. Chemical Engineering and Materials Science, Michigan State University, 2006, his Postdoctoral Research in Chemical Engineering, Massachusetts Institute of Technology, 2009, before he joined University of Michigan in 2010.
At MIT, Tuteja helped develop the first-ever “superoleophobic” surfaces, which resist wetting by extremely low surface tension liquids such as various oils and alcohols. Such surfaces are expected to have a wide range of commercial applications, including stain-resistant textiles and fingerprint-resistant surfaces for flat-panel displays, cell phones and sunglasses. This work was named as one of the top five breakthroughs of the year (2007) in Nanotechnology by Technology Review, one of five new discoveries that will change the world by Chosun Daily, and was also highlighted by National Public Radio, ABC News, CBC News, The New York Times, The Washington Post, Nature Chemistry and over 50 other magazines, newspapers and websites.