Nano-Scale Coating That Repels All Types of Liquids

Nanoscale Coating Repels Nearly Any Liquid Engineers at the University of Michigan have developed a nanoscale coating that repels almost any type of liquid and is expected to facilitate the production of breathable, protective and stain-resistant clothing for use by military personnel and scientists. According to engineering researchers at the University of Michigan, the nanoscale coating, which is at least 95 percent air, repels all types of materials within the broadest liquid range in its class, causing them to bounce off the treated surface. In addition to stain-resistant clothing, the coating could pave the way for clothing that protects military personnel and scientists from chemicals while facilitating breathing, as well as advanced water-repellent paints that significantly reduce friction on ships. Solution droplets that would normally damage your shirt or skin rebound when they contact the newly developed "superomniophobic surface." Anish Tuteja, assistant professor in the departments of Materials Science and Engineering, Chemical Engineering, and Macromolecular Science and Engineering, states: "Any liquid you throw onto the coating bounces off almost without wetting. In similar coatings, liquids with very low surface tension such as oils, alcohols, organic acids, organic bases and solvents stick to them and begin to spread, which is not a desirable outcome." Tuteja is the corresponding author of an article on the coating published in a new issue of the Journal of the American Chemical Society. Tuteja and colleagues tested over 100 liquids and observed that only two were able to penetrate the coating. These were chlorofluorocarbons, chemicals used in refrigerators and air conditioning systems. In a study conducted at Tuteja's laboratory, the surface succeeded in repelling coffee, soy sauce and vegetable oil, as well as toxic hydrochloric and sulfuric acids that can burn skin. Tuteja says the coating is also resistant to gasoline and various alcohols. To apply the coating, researchers use a technique called electrospinning, which uses electrical charge to form thin solid particles from a liquid solution. Researchers have so far coated small screen tiles and fabric pieces the size of postage stamps. The coating is a mixture of rubbery plastic particles of "polydimethylsiloxane" or PDMS and nanoscale cubes containing carbon, fluorine, silicon and oxygen that are resistant to liquids, developed by the Air Force. The texture of the material is as important as its chemistry. The material wraps around the porous structure of the surface it is applied to and creates a finer network within the pores. This structure means that 95 to 99 percent of the coating is actually composed of air pockets, so a liquid in contact with the coating has almost no contact with the solid surface. Because the liquid touches only the fibers of the solid surface rather than a larger area, the developed coating can significantly reduce the intermolecular forces that normally bring two states of matter together. Thus Van der Waals interactions are kept to a minimum. Tuteja explains: "Normally, when two materials come close to each other, they charge each other with a small positive or negative charge and the liquid begins to spread as soon as it contacts the solid surface. We greatly reduced the interaction between the surface and the droplet." Droplets with no reason to spread remain intact, interact only with their own molecules, maintain their round shape and bounce off the coating. One of the liquid classifications that this coating succeeds in repelling is the non-Newtonian category, which includes shampoos, creams, blood, paints, clays and printer inks. These are liquids that change their viscosity depending on the force applied to them. Unlike Newtonian liquids such as water and many other liquids whose viscosity remains the same regardless of applied force, these vary. Viscosity is a measure of a liquid's resistance to flow when force is applied and in some cases is thought of as the thickness of the liquid. Tuteja said: "To date, no one has demonstrated that low surface tension non-Newtonian liquids bounce off." The title of the article is "Superomniophobic Surfaces for Effective Chemical Barriers." Shuaijun Pan, a doctoral student in materials science and engineering, and Arun Kota, a postdoctoral researcher, are the first authors of the article. Joseph Mabry from the rocket propulsion division of the Air Force Research Laboratory is also listed among the contributing authors. The study is financed by the Air Force Office of Scientific Research. Source