Techniques to prevent frost and ice formation on surfaces rely heavily on heating or on liquid chemicals that need to be repeatedly reapplied because they easily wash away. Even advanced anti-icing materials have problems functioning under conditions of high humidity and subzero conditions.
Several unique properties of materials known as phase-switching liquids (PSLs) hold promise as next-generation anti-icing materials. PSLs can delay ice and frost formation up to 300 times longer than state-of-the-art coatings being developed in laboratories.
PSLs are phase change materials that have melting points higher than the freezing point of water (0 °C), meaning they would be solids at temperatures close to that at which water freezes. Such materials include cyclohexane, cyclooctane, dimethyl sulfoxide, and glycerol.
While researchers have known about phase change materials for a long time, their unique anti-icing and anti-frosting properties have not been investigated. In the current work, researchers cooled a range of PSLs to -15 °C, rendering them all solid. Under high-humidity conditions, the solidified PSLs melted directly underneath and in the immediate vicinity of water droplets condensing on the PSLs. The droplets showed the same hopping motion, even at very low temperatures.
PSLs are extremely adept at trapping released heat. This quality, combined with the fact that condensed water droplets become extremely mobile on cooled PSLs, means that the formation of frost is significantly delayed. Eventually, ice forms but some of the PSLs are water-soluble; this contributes to their anti-freezing properties and can help delay ice formation much longer than even the most advanced anti-icing coatings.
PSLs could be used to coat objects like car windshields without compromising the object’s functionality. PSLs also have a range of optical transparencies, can self-repair after being scratched, and can purge liquid-borne contaminants. Because PSLs are solids at low temperatures, they wouldn’t need to be applied as often as liquid anti-icing agents because they would have better staying power.