New Materials Repel Oil

Chemical Engineering Progress, Jan 2008

Researchers at the Massachusetts Institute of Technology (MIT; Cambridge, MA) have developed a new class of materials that can repel oil, a discovery that could have applications ranging from hazardous-waste cleanup to aviation and space travel. For example, such materials could be used to protect parts of airplanes or rockets that are subject to damage from being soaked in fuel, like rubber gaskets and O-rings - vulnerable points in many aerospace applications, says chemical engineering professor Robert Cohen and a member of the research team.

Creating an oil-repelling, or oleophobic, material has been challenging, and there are no natural examples of such a material. The tendency of oils and other hydrocarbons to spread out over surfaces is due to their very low surface tension. The MIT team overcame the surface-tension problem by designing a type of material composed of microfibers that essentially cushion droplets of liquid. When oil droplets land on the material, which resembles a thin fabric or tissue paper, they rest atop the fibers and pockets of air trapped between the fibers. The large contact angle between the droplet and the fibers prevents the liquid from touching the bottom of the surface and wetting it.

The microfibers are a blend of a specially synthesized molecule called fluoroPOSS, which has an extremely low surface energy, and a common polymer. They can be deposited via electrospinning onto many types of surfaces, including metal, glass, plastic and biological surfaces such as plant leaves.

The researchers have also developed dimensionless design parameters that can predict how stable the oleophobicity, or oil resistance, between a particular liquid and a surface will be. Using these relationships, they can design fiber mats that are optimized to repel different hydrocarbons.