Chemistry of 'Wine Legs' Inspires Surface-Skimming Minibots

Miniature robots hold great promise — tiny bots could help with tasks such as environmental cleanups in the future. But finding a way to power these tiny robotic helpers is a challenge because clean, lightweight and compact fuel sources are hard to develop.

Now, a team of engineers from the East China Normal University in Shanghai may have found a solution: They've developed a chemical motor for lightweight robots that can glide along the surface of a body of water. The findings are described in an October study published in the journal Langmuir.

The chemistry-based minimotor works because of a phenomenon called the Marangoni effect, which describes what happens when two liquids with strong surface tensions interact. The most famous example of the Marangoni effect is the so-called "legs" that run down the side of a glass of wine after the liquid in the cup is swirled. Because of this effect, liquids slip and slide alongside each other instead of mixing together. [Biomimicry: 7 Clever Technologies Inspired by Nature]

The team from Shanghai found that concentrated droplets of a solution of polyvinylidene fluoride and dimethylformamide (PVDF/DMF) interacted this way when placed in water — instead of dissolving into the water, the droplet would sit on the surface and spin rapidly, not unlike a motor.

The team tested out the new chemical motor two ways. First, they put tiny lightweight paper rockets and paper goldfish into a petri dish of water and dropped some PVDF/DMF on their tails. The mock minibots immediately started zipping around the dish in wide circles as the droplet spun around like a propeller.

The scientists also tried to use a PVDF/DMF droplet to generate electricity. To do so, they placed a four-armed stirrer that was hooked up to an electromagneton top of a spinning droplet. As the stirrer whirled, it generated electricity. Because the chemical motor doesn't give off any pollution, the researchers said this sort of technology could lead to a new source of clean energy. But, as the arms of the stirrer cut through the water and the droplet, the surface tension of the water decreased, causing the PVDF/DMF "motor" droplet to disperse throughout the water and slow to a halt.

The new study was a so-called proof of concept, meaning that its main goal was to see if the idea worked. Indeed, the chemical motors aren't quite ready for industrial use, as the current version can propel a paper rocket for only a couple of minutes. But the scientists said they are optimistic that further exploration of the Marangoni effect could lead to a fleet of lightweight, energy-efficient aquatic robots skimming across the water.

Originally published on Live Science.

Dan Robitzski
Staff Writer
Dan Robitzski is a staff writer for Live Science and also finishing up his master's degree at NYU's Science, Healthy & Environmental Reporting Program. Formerly a neuroscientist, Dan decided to switch to journalism and writing so that he could talk about transparency and accessibility issues within science. When he's not writing, he's either getting beaten up at fencing practice or enduring the dog breath of his tiny, affectionate Chihuahua. He also spends too much time on Twitter at @danrobitzski.