Material Folds Into A Straw When Exposed To Water

William Wong places a drop of colored water on his self-folding material. ANU

A self-folding straw has been manufactured that turns from a flat strip to a cylinder on encountering water. Besides potentially producing a new line in “just add water” origami, the concept could be used for sampling liquids in potentially toxic environments.

Mimosa pudica is a plant native to South America whose leaves fold up when touched. Artificial materials have been produced that can do something similar on a very small scale, but Australian National University postgraduate student William Wong wanted to expand the scale of operation.

In Science Advances, Wong has announced that stacking a layer of polycaprolactone nanofibers on polyvinyl chloride microfibers creates a material he calls Janus for the opposing behaviors of the two layers.

The polycaprolactone is attracted to water, while the polyvinyl chloride repels water. The attraction of the top layer causes Janus to wrap around any water it encounters, while the hydrophobic underside prevents the water from escaping.

“If we place a drop of water at one end, the material will curl into a tube, delivering the liquid up to 15 centimeters away,” Wong said in a statement. The process is reversible using ethanol, and has the potential to lead to far more elaborate constructions.

“This enables a rapid self-assembly of complex shapes, such as bent, curved and splitting channels, that are a building block for micro-fluidic systems,” Wong said.

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