Smears of wine running down the side of a glass have inspired scientists to produce tiny chemically-driven engines that run on electricity generated in water.
When wine is sloshed up the sides of a glass, the different surface tensions of the alcohol and water components of the beverage effectively pull the liquid up the glass until its weight overcomes the force and pulls it down again.
The phenomenon is known as the Marangoni effect and was first observed in 1855 by physicist James Thomson. He termed it the “tears of wine”.
Now, physicists led by Lidong Zhang of the East China Normal University in Shanghai, China, have co-opted the Marangoni effect to produce droplets that rotate rapidly in water, producing chemical-free energy.
Sadly, Zhang and his colleagues do not use a robust claret or a cheeky little Beaujolais to create their micro-engines, opting instead to use a combination of polyvinylidene fluoride and dimethyl formamide.
The mixture, formed into a tiny droplet, swells on contact with water, and the Marangoni effect causes it to spin rapidly. Despite weighing only 22 milligrams, the droplet produced enough kinetic energy to propel a waterborne paper rocket weighing 32 milligrams for a distance of more than 560 centimetres.
As the video here shows, the team also tested the droplets using paper goldfish, and X-shaped pieces of cardboard used for mixing chemicals into water.
The energy released by the droplet can be converted into electricity using an electromagnetic generator. The scientists, writing in the American Chemical Society journal Langmuir, suggest the wine-inspired engines could be useful for miniature robotics applications.
Andrew Masterson is a former editor of Cosmos.
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