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Surface Chemistry


The hard-hitting science behind crepes and beauty pageants

by Melissa Gilden
July 9, 2019 | A version of this story appeared in Volume 97, Issue 28


Critical crepe density

A photo of a crepe in a pan with eggs and other ingredients.
Crazy crepes: Just for fun, physicists modeled how to cook the perfect crepe.

Whether it be pancakes, waffles, or aloo paratha, most of us cannot resist a carb-laden breakfast dish. If it’s crepes that you crave, we now know the best technique to achieve the perfect thickness and uniformity of the sweet or savory snack, thanks to a couple of crepe-cognizant physicists.

Edouard Boujo of École Polytechnique and Mathieu Sellier of the University of Canterbury say that they were challenged by Sellier’s wife to use physics to determine the optimal way to cook a crepe. They accepted that challenge, publishing the first-known mathematical model of crepe making in Physical Review Fluids (2019, DOI: 10.1103/physrevfluids.4.064802).

If you’ve ever tried to make a crepe at home, or even an omelet, you may have casually thought that lifting the pan and rotating it around to get the batter to cover the entire pan seemed like the best way to cook it. But for the purposes of this modeling exercise, Boujo and Sellier took into account a number of factors beyond a simple flick of the wrist. In their paper, the physicists demonstrated that the pan must indeed be rotated around a vertical axis (imagine a vertical line through the center of the pan), tilted in a swirling motion to employ gravity to spread the batter throughout the pan. Boujo and Sellier also had to take into account the interaction between the substrate kinematics (pan rotation) and the solidification of the liquid layer (temperature-dependent viscosity increase of the batter) in the model they describe.

Think you can make a perfect crepe without giving the pan a whirl? Highly unlikely, the scientists say. If the pan is left horizontal, the batter tends to solidify before reaching the far edges of the pan, resulting in a thicker, pancake-like product, which this Newscripter doesn’t particularly care for.

While the swirl technique may be the best way to produce the perfect vehicle for Nutella and bananas, Boujo and Sellier’s model has plenty of real-world engineering applications—for example, in chocolate-manufacturing, surface-coating, and paint-drying processes.

So the next time you decide to make a crepe at home, honor the physicists before you by giving a bit of thought to all the forces acting on your solidifying batter. Just be careful not to let it burn.


Beauty and grace and elephant toothpaste

A photo of Camille Schrier performing the elephant toothpaste reaction that helped earn her the title of Miss Virginia.
Credit: John Herzog
Chemistry gets the crown: Camille Schrier performs the elephant toothpaste reaction in the talent portion of the Miss Virginia competition.

Anyone who’s ever watched a Miss America competition is familiar with the usual talents presented. Trained classical ballerinas, pianists, and opera singers show off their finely honed skills in an attempt to clinch the crown. But last month, 24-year-old Virginia Commonwealth University graduate student Camille Schrier turned the pageant world on its head with a showstopping chemistry demonstration that earned her the title of Miss Virginia.

Schrier performed a demonstration that many a C&EN reader will be familiar with: the elephant toothpaste experiment. To make elephant toothpaste, one normally combines hydrogen peroxide with household dish soap, yeast or potassium iodide, and maybe even a bit of food coloring for drama.

The exothermic elephant toothpaste reaction uses a catalyst—usually the iodide from potassium iodide or catalase from baker’s yeast—to decompose hydrogen peroxide into oxygen gas and water. The oxygen gas given off combines with the dish soap and food coloring for a resulting explosion of foamy by-product that is a visual delight for children and adults alike.

We here at Newscripts headquarters were very happy to hear that a science demonstration took center stage at the Miss Virginia pageant. We can’t wait to see what demonstration Schrier performs when she competes for the title of Miss America.

Melissa Gilden wrote this week’s column. Please send comments and suggestions to


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