Understanding Wine “Legs,” the Marangoni Effect and Minibot Motors

wine legs Marangoni effect

As wine enthusiasts know, the “legs” or “tears” that run down a glass after a gentle swirl can yield clues about a wine’s alcohol content. Interestingly, the physical phenomenon — called the Marangoni effect – responsible for creating these tears can be harnessed for practical applications. Scientists have developed little motors that can run based on this phenomenon. The team reported this work the paper “Marangoni Effect-Driven Motion of Miniature Robots and Generation of Electricity on Water,” published in ACS’ journal Langmuir.

Watch a Video on the Marangoni Effect and Its Applications

Miniature robots in water have been shown to clean up pollutants and perform other useful tasks. But fueling them has been a challenge. One promising method to propel little machines through water involves using chemical reactions to produce bubbles, which then get ejected and push the robots around. However, this approach requires the use of expensive catalysts. To eliminate the catalysts but still propel the machines on water, Lidong Zhang and colleagues turned to the Marangoni effect in which fluid moves due to changes in surface tension.

To build their minimotors, the researchers created concentrated droplets of polyvinylidene fluoride (PVDF) and dimethyl formamide (DMF) that, due to the Marangoni effect, rotate rapidly on water. Testing showed that the droplets could propel paper goldfish hundreds of centimeters without emitting any pollutants into the air. Also, with the addition of an electromagnetic generator, the kinetic energy could be converted to electrical energy, a feature that could broaden the propeller’s applicability.

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