Issue Date: November 21, 2011
Peanut Models, Stencil Cards, Acid-Indicating Umbrellas
Dismayed by the price of your college bookstore’s molecular model kit? Need more atoms or bonds than the kit holds? Never fear, Newscripts readers, a solution is as close as the nearest box of packing peanuts.
Yes, packing peanuts—in particular, the biodegradable ones made of starch. Several years ago, as a graduate student at the University of Texas, Austin, Sean M. Ragan came up with the idea of sticking them together by moistening the ends. “You can use your tongue, but a sponge is probably a better idea,” he says.
Ragan has made many molecules with the peanuts, from compounds as small as methane to those as large as buckminsterfullerene. The peanuts can be colored, but Ragan recommends staying away from water-based inks. Keep the molecules dry and they’ll last a while, he says: Ragan’s buckyball survived for more than four years.
Packing peanuts haven’t been Ragan’s only chemistry-related inspiration over the years. As a chemistry tutor, he noticed that some people have a hard time drawing cyclohexane conformations. Wanting something to advertise his services, he came up with an idea for a business card that doubled as a stencil for those oh-so-tricky chairs.
Design in hand, he sent it off to a laser cutting shop, along with a few sheets of transparent fluorescent plastic. Included on the card is a note to “flip card to flip chair.”
Ragan had hoped that students would find the card useful enough to keep handy and share with their friends or classmates. Now a writer for do-it-yourself magazine Make, Ragan chuckles when asked whether the cards did in fact help his tutoring business. They’ve served him far better as a networking tool in the design community than they did for chemistry tutoring, he says.
Ragan isn’t the only one who likes turning something useful into something even more useful. Hong-Wen Gao and Xin-Hui Xu of China’s Tongji University have developed a coating that incorporates an acid-base indicator. When painted onto an umbrella, it changes color anytime the umbrella is exposed to acid rain.
Gao and Xu used Congo red, 3,3'-[[1,1'-biphenyl]-4,4'-diylbis(2,1-diazenediyl)]bis[4-amino-1-naphthalenesulfonic acid], which shifts from red at pH 5.2 to blue at pH 3.0. Congo red is soluble in aqueous solution, so the researchers bound the compound to barium sulfate to transform it into a coating.
Analysis of the Congo red-BaSO4 material showed a stacked, sandwichlike structure with Congo red molecules binding through their sulfonic acid groups to link layers of BaSO4. In aqueous solution, the complex creates a “thick dark-red semifluid,” Gao and Xu say.
Congo red decomposes under ultraviolet light and therefore won’t last long if it’s used on something that gets a lot of sunlight. So Gao and Xu painted it onto an umbrella, which gets infrequent UV exposure, alternating the Congo red sections with a control coating. When they exposed the umbrella to simulated acid rain with a pH less than 5, the indicator-painted segments turned purple (Chem. Commun., DOI: 10.1039/c1cc15435d).
Gao tells Newscripts that he hopes the material can be used in the future to alert people to acid rainfall.
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © American Chemical Society