Designing Omniphobic Surfaces using Nanostructured Coatings: Applications in Super Liquid Repellency, Ice-phobicity, Friction Reduction & Fog-Harvesting

K.-C. Park, S. Sreenivasan, R.E. Cohen, G.H. McKinley
Massachusetts Institute of Technology, US

Keywords: hydrophobic, self-cleaning, fog-harvesting, solar desalination, photophilic, photovoltaic cell

Summary:

Many different structured surfaces with a wide range of surface chemistries and topographies have been investigated for controlling the wetting (or non wetting) properties of a fluid/solid interface. Experimental advances in nanofabrication have led to the ability to achieve unprecedented control over the micro- and nano-texture of a substrate and this can result in almost perfect ultrahydrophobicity. Very few structured surfaces to date, however, have been able to achieve super-oleophobicity; i.e. resistance to wetting by low interfacial tension liquids such as hydrocarbons. Fluorinated silsesquioxanes are nanometer-scale caged molecules that can be molecularly- dispersed in a range of polymers to systematically control both hydrophobicity and oleophobicity (oil-repellency). Microtextured re-entrant structures coated with FluoroPOSS are the most oleophobic surfaces produced to date, with alkane contact angles greater than 160˚ and low wetting hysteresis. We have also developed single-step dip-coating and spray-coating processes for applying such coatings to a wide-range of substrates. Applications of these nanostructured coatings include fabrics with enhanced solvent/oil resistance, surfaces for reducing environmental fouling and frictional dissipation, efficient separation of oil/water dispersions, reduction of ice- and gas hydrate-adhesion as well as ‘fog-harvesting surfaces’ that greatly enhance our ability to collect solar-desalinated water from wind-borne fog.