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Droplets of liquid with a protective coating can be joined into super-long chains of up to 1.7 metres.

Liquid marbles consist of droplets that are covered by one or more layers of solid particles.聽Many of them are too soft to be handled and are easily destroyed by mechanical stress 鈥� particularly those that are larger than capillary length, a factor relating to gravity and surface tension. At 20掳C, the capillary length of water is 2.7 millimetres.

Syuji Fujii聽at the Osaka Institute of Technology in Japan and his colleagues had previously developed liquid marbles that can be picked up and piled on top of each other by hand or using tweezers. These nearly spherical marbles were created by rolling millimetre-sized droplets of liquid on a bed of small hexagonal discs made of a water-repellent plastic called polyethylene terephthalate, or PET.

Now they have shown that it is possible to join these near-spherical droplets together to form a chain by sequentially prodding two droplets with a small sharp object, such as a pipette or needle.

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They created the 1.7 metre chain by joining around 300 individual liquid marbles together, a process that took more than 10 hours and required liquid to be added because some was lost to evaporation.

By using small implements to shape liquid marbles, the team was also able to create chains that looked like all the letters of the alphabet.

The researchers also developed liquid marbles consisting of particles of two different sizes by joining a near-spherical liquid marble with a cube-shaped one. This created a micro-pump: liquid flowed from the near-spherical marble into the cube-shaped one.

Such micro-pumps could be useful for small-scale chemical reactions, says Fujii. 鈥淭his automatic liquid flow is advantageous to mix the liquids.鈥� He says the the ability to control the direction of flow could be useful for micro-reactors for chemical or biological reactions.