surface construction
Actually realizing and constructing a textured and roughened surface to enable icephobicity is, as one would imagine, the most crucial step for real world use. While researchers are exploring the most efficient icephobic surfaces, they are often outside the realm of possibility for actual manufacturing and application. In this section, we will discuss various methods and discoveries for icephobic surface construction, with an emphasis on ones plausible for mass manufacturing and real world applications.
The biggest threat to superhydrophobic surfaces not being icephobic is frost formation which is common on hydrophobic surfaces and can significantly increase ice adhesion. An alternate design to hydrophobic surfaces has been lubricant-impregnated surfaces which, in simpler terms, are ultrasmooth surfaces opposed to nano-textured surfaces. These surfaces exhibit droplet roll-off because of how smooth they are and have also been observed to have anti-frosting characteristics. Seeing how this method could possibly be used in conjunction with other methods to add inhibition of frost formation to icephobic surfaces is research continuing now. On the flip side nanoscale roughness (extremely small customized bumps on the surface) aims to inhibit the Wenzel state, keeping the drops in the Cassie state so they coalesce and then roll off the surface. This method is much more common for icephobic surface construction and more research has gone into manipulating and manufacturing different nano-textures and varying roughness to achieve better icephobicity. For example, researchers have designed a fabrication process that produced nanoroughness on micropillars, this was done on top of a pre-existing surface lithographically and created an icephobic surface. The texture ended up degrading superhydrophobicity because portions of the texture (the “sidewalls”) had a tendency to hold onto water droplets when the surface was squeezed. However, this technique, and others like it, remain high in price and have limits in terms of size of construction and the time it takes to synthesize.
The most fruitful surface construction for icephobic surfaces has come when the two methods are combined. Researchers in Shanghai have very recently discovered a method that assembles a surface using ultrathin MXene multilayers. This uses methods very similar to nano-structuring but creates a very smooth surface. This allows the surface to be self-cleaning and, in some ways, self-healing because it avoids degradation over time by inhibiting adhesion from many liquids. In this way, the surface is superhydrophobic as well. The surface absorbs solar thermal energy which allows it to reach temperatures that prevent water from freezing and melt any pre-formed ice or thick frost. The nano-layer construction is utilized to achieve transparency. So, while the qualities of icephobicity and superhydrophobicity are maintained, the surface also achieves a level of transparency suitable for windows on houses and automobiles. This makes it one of the most plausible surface constructions we have seen and at only 4.1 dollars per square meter, we may see it in vehicles and other vehicles very soon.