Phase-changing liquid coating keeps surfaces frost-free for longer
In cold places, ice and frost can be more than an annoyance – it can be downright dangerous for cars and planes. Now researchers from the University of Illinois at Chicago (UIC) have developed a new anti-icing material that can apparently keep ice at bay much longer than existing technologies.
There are no shortage of methods for preventing ice building up where it's not wanted. Heat is a common factor – some materials trap it from sunlight, while others are powered, like electrified concrete at airports or carbon nanotubes in aircraft wings. Other materials are impregnated with salt, or repel water so it all just slides off.
The new material is made of phase-switching liquids (PSLs), and it also uses heat to keep ice away. Strangely enough, the heat comes from the water droplets themselves, which the PSLs are good at trapping. Generally these materials have a higher melting point than that of ice, so they stay solid at temperatures after ice turns back into water.
"At sub-zero temperatures, all PSLs turn solid," says Rukmava Chatterjee, first author of the study. "So, on a winter day, you could coat a surface where you don't want icing with a PSL material and it would remain there much longer than most deicing liquids, which demand frequent reapplication."
The researchers thought to try PSLs when they noticed in previous studies that water droplets danced around on the surface of these materials after condensing. On investigation, it was found that this was because the water was releasing heat into the materials, which caused them to warm up and melt, in turn repelling the water.
For the new study, the team cooled several different types of PSLs to -15° C (5° F), turning them solid. They then placed them into high humidity conditions and watched how water condensed on their surfaces. Sure enough, the solid PSLs melted and kept the water droplets at bay. The team was actually surprised it still worked at temperatures this low.
"It turns out that PSLs are extremely adept at trapping this released heat," says Sushant Anand, corresponding author of the study. "This quality, combined with the fact that condensed water droplets become extremely mobile on these cooled PSLs means that the formation of frost is significantly delayed. Yes, at a certain point, ice does eventually form and that is inevitable, but some of the PSLs we tested are water soluble, and this contributes to their anti-freezing properties and can help delay ice formation much longer than even the advanced anti-icing coatings."
Because they can work at such low temperatures, the team says the new material can keep surfaces ice-free for up to 300 times longer than existing anti-icing coatings, and it can work even when applied as a thin film. PSLs have a few other bonuses too – they can be made to be transparent, self-repair from scratches and keep contaminants in liquids from sticking to them.
The research was published in the journal Advanced Materials. The team describes the materials in the video below.