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|Title:|| Supercooled Water Drops Do Not Freeze During Impact on Hybrid Janus Particle-Based Surfaces
|Authors:||Madeleine Schwarzer, Thomas Otto, Markus Schremb, Claudia Marschelke, Hisaschi T. Tee, Frederik R. Wurm, Ilia V. Roisman, Cameron Tropea, and Alla Synytska|
|Publication Info:||Chemistry of Materials, 2019, 31 (1), 112–123 DOI: 10.1021/acs.chemmater.8b03183|
Whether it’s frozen fingers after scraping ice off your car’s windshield or downed power lines in an ice storm, winter weather can be downright dangerous. That’s why scientists have been studying the formation of ice from precipitation on different surfaces for years, trying to develop coatings that prevent ice formation. Now new findings from Germany demonstrate that there’s at least one type of coating – made from mixtures of of polymer-coated particles – that completely resists freezing.
Ice formation on a surface depends on several factors, from the temperature of the water to the strength of its impact on the surface. Neither of these factors are easily controlled; they depend on the severity of the winter storm.
However, the type of surface also matters. That’s where these researchers focused their attention. Surfaces that are hydrophobic can chemically repel water – causing it to bead up like a drop on your raincoat. Hydrophobic surfaces can also prevent ice from forming, but they’re easily damaged. And surfaces that are very slightly rough resist ice formation, but once ice does form it grips tightly and is even more difficult to remove.
To make these new ice-repelling coatings, called hybrid Janus particle-based surfaces, the researchers created very small particles (100x smaller than a human hair). These particles slightly roughen the surface. Both hydrophobic and hydrophilic molecules are added to the surface of the particles. Hydrophilic molecules are the opposite of hydrophobic: they attract water. Attracting water sounds like the opposite of what you’d want in an ice-repelling coating – so why do these surfaces repel ice so well?
It turns out that combining a surface that repels water with a surface that attracts water has a huge impact on the behavior of a water droplet hitting that surface. Normally, a water droplet beads up on a surface (Figure 2, a and b). On these hybrid hydrophobic- and philic- surfaces, the droplet instead breaks apart (Figure 2, h and i). This unique behavior means that the contact time and area of the water droplet on the surface are too small for ice to form.
These hybrid Janus particle-based coatings can be used to cover large surfaces, and once applied, these surfaces are both scratch- and impact-resistant. While there are plenty of spray-on deicers, why not build a surface that resists ice right from the start?