Frost formation and ice adhesion on superhydrophobic surfaces
Click to view
ESEM images of frost formation on a superhydrophobic surface comprising of an array of hydrophobic square posts with width, edge-to-edge spacing, and aspect ratio of , , and 7, respectively. (a) Dry surface. [(b)–(d)] Snapshot images of frost formation on the surface. The intrinsic water contact angle of the hydrophobic coating on the posts is . The surface is maintained at a temperature by means of a cold stage accessory of the ESEM. At the beginning of the experiment the chamber pressure is maintained at , well below the saturation pressure to ensure a dry surface. The vapor pressure in the chamber is then slowly increased until frost nucleation is observed. Frost nucleation and growth occurs without any particular spatial preference on all of the available area including post tops, sidewalls, and valleys due to the uniform intrinsic wettability of the surface.
Click to view
Droplet impact measurements on dry and frosted superhydrophobic surface conducted using droplets of 1 mm radius impacting the surface at velocity . (a) Top view SEM image of the representative Si post array surface with width, edge-to-edge spacing, and aspect ratio of , , and 1, respectively. (b) Photograph of the dry surface along with sequential high-speed video images of droplet impact. As expected, droplet recoils from the surface, as the antiwetting capillary pressure is greater than the dynamic wetting pressures (see Ref. 25). (c) Photograph of the frosted surface along with sequential high-speed video images of droplet impact. Frost alters the wetting properties of the surface, making the surface hydrophilic, causing Cassie-to-Wenzel wetting transition of the impacting drop, subsequent pinning and formation of “Wenzel” ice on the surface.
Click to view
Plot of the measured ice adhesion strength of the textured surfaces normalized by the measured ice adhesion strength of the smooth surface as a function of total surface area normalized by the projected area. The ice adhesion measurements on textured and smooth PDMS surfaces were conducted at using the apparatus described in supplementary material (Ref. 17). The normalized ice adhesion strength increases with normalized surface area and shows a strong linear trend. The best linear fit to the data (solid line, correlation coefficient ) has a slope of one and passes through the origin (extrapolated using a dashed line) indicating that ice is contacting all available surface area. Insets [(a)–(d)] are top view optical images of representative replicated PDMS post arrays from sparse to dense spacing (, , , 30, 15, and , respectively) showing the excellent quality of replication.
Article metrics loading...
Full text loading...