(379a) Drop Motion On Superhydrophobic Surfaces

This paper presents results on the development of superhydrophobic nanofiber surfaces for use in separation of stable water in oil emulsions. Superhydrophobic surfaces are defined as having a water contact angle exceeding 150°. The most hydrophobic polymer known is PTFE, with a water contact angle of approximately 120°. However, surface wetting properties of polymers can be enhanced by creating roughness. A simple and inexpensive way to induce surface roughness is to use the technique of electrospinning to produce polymeric nanofiber mats. The roughness at the nanoscale of these surfaces enhances surface properties by lowering the surface energy and increases the water contact angle. Using the electrospinning technique, four different polymeric nanofiber mats were produced that were superhydrophobic : poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), polypropylene, poly(4-methyl-1-pentene) and polystyrene. Since these surfaces have water contact angles above 150°, water droplets roll across the surface as near spherical droplets. Experiments were carried out to determine how much force was required to move droplets along these surfaces. Due to the high contact angle, water droplets have low contact area with the surface which reduces the force required to move the droplets along the surface. It was determined that the force required to move drops along these hydrophobic surfaces was less than the force of gravity. Since these nanofiber surfaces are porous, they can be used to remove low concentrations of water in oil.