Robotic water strider is propelled by surface tension – and alcohol

Robotic water strider is prope...
An illustration of a water strider (left) alongside the robot
An illustration of a water strider (left) alongside the robot
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An illustration of a water strider (left) alongside the robot
An illustration of a water strider (left) alongside the robot

You may think that water strider insects move across the water's surface simply by wiggling their legs, but they actually utilize what is known as the Maragoni effect. Scientists have now utilized the phenomenon in a tiny, silent, water-striding robot.

The Maragoni effect is defined as "the mass transfer along an interface between two fluids due to a gradient of the surface tension." Water striders harness it by secreting water-insoluble compounds called lipids, creating a surface tension imbalance that pulls them forward. Led by Asst. Prof. Hassan Masoud, a team at Michigan Technological University built a small robot that works in the same fashion.

The device sits on a side-by-side set of pontoon-like floats. Instead of using lipids for propulsion, though, it creates the surface tension imbalance via the controlled release of isopropyl alcohol.

The liquid is contained within the bot's cylindrical body, and is dispensed out of a horizontally swivelling nozzle in the rear. By remotely controlling the direction in which that nozzle is facing, it's possible to steer the robot in real time. Its speed is controlled by varying the alcohol's flow rate.

In its current incarnation, the robot has a top speed of about 100 mm per second, and a fuel efficiency of around 600 mm per milliliter of alcohol. The scientists are working on improving both of those figures, in hopes that the technology could one day find use in applications such as wildlife observation or environmental monitoring in difficult-to-access locations. It's even possible that autonomous "swarms" of the robots could work together on such tasks.

The robot was recently described in a paper published in the journal Bioinspiration & Biomimetics, and can be seen in action in the video below.

It should be noted that researchers at the Harbin Institute of Technology and Harvard University have previously designed water-strider-inspired robots, although they didn't utilize the Maragoni effect in the same fashion as the Michigan Tech bot.

Linear Speed Test

Source: Michigan Technological University

A speed test, which plays back at double-speed. Seriously? If it played at 1x speed, then we would all be able *see* the **actual** speed...
I love hope it is powered by tension and alcohol - like many of us!
This invention reminds me of the glue in water experiment (
I would be interested to see if the solvent system can be swapped out for deionized water, therefore, creating propulsion by solute concentrations. The effect would naturally be much weaker than that of surface tension but could be run more sustainably and continually with solar input.
Nice one Ben West. :)
Achmed Adolf Wolfgang Khammas
Crazy ... I've played with little toys on water which were propelled the same way ... 60 years ago!!