Liquid marbles look and sound cool 鈥� but they could also be used to make miniature reactors and sensors.
Syuji Fujii at the Osaka Institute of Technology in Japan and colleagues have created liquid marbles that can be easily moulded into different shapes, making 3D letters and mini disco balls.
The research was inspired by aphids, who make liquid marbles by coating honeydew with wax particles so that they can easily transport them.
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The marbles consist of a droplet of liquid surrounded by small hexagonal discs made of water-repellent polyethylene terephthalate, the plastic commonly known as PET.
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鈥淭he droplet is covered with plates, which work as an armour,鈥� says Fujii. The team have successfully created these armoured droplets from liquids such as water, glycerol and diiodomethane.
The shape of the marbles depends on the relative sizes of the droplets and plates. When the droplets and plates are similar sizes, you get cube-shaped, tetrahedral or pentahedral marbles. When the droplets are larger than the plates, you get marbles that are nearly spherical.
鈥淭he liquid droplet tends to be spherical in order to decrease surface tension,鈥� says Fujii. But the plates pack closely on the droplet, causing its surface to become hard and letting its shape deform.
The plates self-assemble into ordered hexagonal arrangements. The researchers aren鈥檛 yet sure exactly why, but believe it may be to do with lateral capillary forces 鈥� in which water-repelling objects on a liquid surface interact with each other and gather together.
If the liquid marbles are made from transparent plates, they can be used as sensors to detect the presence of gases, says Fujii. By making the droplet from liquid containing phenolphthalein, for example, the marble鈥檚 colour changes to pink in the presence of ammonia vapour.
They could also be used to create different-shaped miniature reactors used to catalyse chemical reactions.
Journal reference:听听Advanced Functional Materials,听
