Sunday, April 28, 2019
Good example
Here's a POSITIVE example of science journalism, hitting two of the subjects I suggested yesterday. Static friction, and glues and waxes.
A new way of de-icing large surfaces.
The researchers overcame a major limitation of previous ice-repellent coatings—while they worked well on small areas, researchers found in field testing that they didn’t shed ice on very large surfaces as effectively as they had hoped. That’s an issue, since ice tends to cause the biggest problems on the biggest surfaces—sapping efficiency, jeopardizing safety and necessitating costly removal. They cleared this hurdle with a “beautiful demonstration of mechanics.” Anish Tuteja, an associate professor of materials science and engineering, described how he and his colleagues turned to a property that isn’t well-known in icing research. “For decades, coating research has focused on lowering adhesion strength—the force per unit area required to tear a sheet of ice from a surface,” Tuteja said. “The problem with this strategy is that the larger the sheet of ice, the more force is required. We found that we were bumping up against the limits of low adhesion strength, and our coatings became ineffective on large surfaces.I've noticed this effect in trying to break an ice dam on the roof, or defrosting an old refrigerator. Prying doesn't work unless you vertically cut the ice into pieces less than six inches across. Their analogy is unnecessarily complex:
“Imagine pulling a rug across a floor,” said Michael Thouless. “The larger the rug, the harder it is to move. You are resisted by the strength of the entire interface between the rug and floor. The frictional force is analogous to the interfacial strength. But now imagine there’s a wrinkle in that rug. It’s easy to keep pushing that wrinkle across the rug, regardless of how big the rug is. The resistance to propagating the wrinkle is analogous to the interfacial toughness that resists the propagation of a crack.”Simpler analogy, understandable by everyone... not even an analogy. A literal example of the process itself. How do you de-ice your car's windshield? Do you insert the scraper at one end and pry off the ice in one sheet? No. You chop chop chop chop scrape, chop chop chop chop scrape. Given the universality of this experience, it's sort of surprising that it didn't inspire this engineering solution a long time ago. ¶ 8:17 AM
