For all these reasons, and others, science has performed many studies to develop material(s) which can prevent the formation of ice. These materials are called ice-repellent or icephobic.
Very hydrophobic materials, that is materials with a very high water contact angle, can help in preventing ice formation. Although these materials work very well even at low temperatures (i.e. down to -25 oC), they are effectively icephobic only in an environment with relatively little humidity. In cases of high humidity, on the contrary, they seem to favor the formation of ice.
This is because they have a very high surface area; in the presence of high levels of humidity, water droplets are easily adsorbed on the surface of the materials, and then condense into an ice layer.
Icephobic Surfaces: Innovative Approach
An innovative approach to develop an icephobic surface material was recently reported by some researchers of Harvard University. The work was developed as a cooperation between the Wyss Institute, the Harvard School of Engineering and Applied Sciences, the Department of Chemistry and Chemical Biology and the College of Natural Sciences of Puerto Rico, and was published in ACS Nano on the 10th of June, 2012.
Slippery Liquid-Infused Porous Surfaces (SLIPS)
The system developed by the researchers is called Slippery Liquid-Infused Porous Surface (SLIPS). In the SLIPS system, the researchers obtained a icephobic surface by making the surface itself very, very smooth, and almost defect-free with the addition of a layer of a very hydrophobic, or water resistant, fluid. Since the surface repels water, it is impossible for the water droplet to stick to the surface, become solid and form an ice film.
Dr. Philseok Kim, lead author of the study, explained the process to Decoded Science: “To create a SLIPS coating on a solid surface, the first step is making the surface very rough; in this way, it will be able to retain the hydrophobic fluid. This is done with an electrochemical process, already tested by our group for different applications. Subsequently, the surface is covered with droplets of an appropriate hydrophobic lubricant fluid, the perfluoroalkylether (Krytox® 100).
The film formed is very thin, between 8 and 10 μm; it is like a coating of paint, but with excellent anti-sticking properties.
We performed this experiment on aluminum surfaces, but the same process can be applied to other materials too.”
Ice-Repellent Materials: Clear Difference
Aluminum sheets prepared like this underwent through several deep freezing / heating cycles, to test the ice formation and its melting, and their behavior was compared with untreated standard aluminum sheets.
The difference between the two materials was very clear, as the SLIPS aluminum sheets accumulated much less ice. In one experiment in particular, both surfaces were kept at -2 oC for about 2 hours, with a relative humidity of 60%; after this treatment, the untreated aluminum sheet was completely covered in ice while only 20 % of the surface of the SLIPS sheet was covered. This video shows very well the efficiency of the SLIPS coating.
According to Dr. Kim: “This work introduces a completely new technology, a defect-free lubricating liquid film. This outperforms all the existing icephobic solutions, as ice adhesion is about two orders of magnitude lower than reported for the best state-of-the-art materials.” This anti-ice treatment, a successful method of creating ice-resistant metal surfaces, may have implications in a number of industries.
P. Kim, et al. Liquid Infused Nanostructured Surfaces with Extreme Anti-Ice and Anti-Frost Performances. (2012). ACS Nano, 10.1021/nn302310q.
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