Nanocomposite Coating Offers Protection Against Assortment of Agents

  • Published
  • By Robert White
  • Office of Scientific Research
ARLINGTON, Virginia --  Research funded by the Air Force Research Laboratory has resulted in a coating that shields surfaces from myriad liquids, including toxic hydrochloric and sulfuric acids. The coating also provides protection against the coffee, soy sauce and vegetable oil, and has proved resistant to resistant to gasoline and various alcohols. This groundbreaking research has a history steeped in academia and made possible by the ongoing support of AFRL's Air Force Office of Scientific Research (AFOSR).
In 2006, AFRL Program Manager Dr. Charles Lee provided funding for Professor Gareth McKinley at the Massachusetts Institute of Technology (MIT) to explore nanocomposite technology for Defense applications. Anish Tuteja, then an MIT doctoral student, was exploiting the unusual surface properties of a nanocomposite with fluorinated nanoparticles, to create a superoleophobic surface.

Tuteja is currently an assistant professor of materials science and engineering at the University of Michigan in Ann Arbor. He was awarded a Young Investigator Program grant from AFOSR in 2011, and continued to conduct the research begun at MIT. His team included doctoral student Shuaijun Pan and postdoctoral researcher Arun Kota, as well as collaboration with AFRL's Dr. Joseph Mabry.

The team's latest paper, "Superomniphobic Surfaces for Effective Chemical Shielding," published in the Journal of the American Chemical Society, describes surfaces that effectively perform as chemical shields against virtually all liquids. Surfaces are prepared using a nanoscale coating--approximately 95 percent air--that repels liquids of any material in its class, causing the liquids to literally bounce off the treated surface. The surfaces "possess hierarchical scales of re-entrant texture that significantly reduce the solid−liquid contact area."

It all comes down to controlling how much contact the liquid has with the treated surface. To gain this control, the researchers apply the nanoscale coating with a process called electrospinning--using an electric charge to create fine particles of solid derived from a liquid solution. The coating is a mixture of cross-linked "polydimethylsiloxane," or PDMS, and liquid-resisting nanoscale cubes developed by the Air Force that contain carbon, fluorine, silicon and oxygen. While the material's chemistry is important, so is its texture, because it hugs the pore structure of whatever surface it is applied to and creates a fine web of air pockets within those pores: any liquid in contact with the coating is barely touching a solid surface. By effectively eliminating the contact between the treated surface and the liquid, there is almost no incentive for the liquid to spread, so the droplets stay intact, interacting only with molecules of themselves, and maintaining their spherical shape.

This program is of particular interest to the Air Force and the Department of Defense for possible use in self-cleaning surfaces (in particular, integral breathable protective Chemical/Biological Warfare defense in uniform clothing and sensor systems), improvement of thermal management efficiency in phase change cooling systems, fuel purification and the control of oil and fuel leakages in rockets and airplanes.
This AFRL-funded discovery could also benefit countless others with myriad possible applications: protection from chemical/biological agents; self-cleaning apparel; effortless thermal management; fuel purification; and better control of leaks--especially oil and fuels. The research team tested more than 100 liquids and found only two that were able to penetrate the coating, both of them chlorofluorocarbons--chemicals used in refrigerators and air conditioners.