Liquid origami

A French team has created the first mini-origami figures that fold themselves around droplets of water.

FOLD ME. As it evaporates, a water droplet bends a plastic sheet into a 3-millimeter-wide pyramid. The same mechanism could work at microscopic sizes. C. Py and C. Baroud/ESPCI

Benoît Roman of the Institute of Industrial Physics and Chemistry in Paris and his colleagues cut shapes out of flat plastic sheets and then dabbed them with water.

The plastic is of a type that attracts water molecules, and as a droplet evaporates and shrinks, that attraction wins over the plastic’s tendency to stay flat. Each droplet “wraps itself like in a blanket to minimize its surface of contact with air,” Roman says.

However, once the water completely evaporates, the folds open back up. Roman says special glues activated by ultraviolet light might keep them in place.

The team reports in the April 13 Physical Review Letters that, so far, it has fashioned millimeter-size cubes, pyramids, faceted spheres, and calzone-shaped objects. But Roman says the technique could easily be scaled down by orders of magnitude.

Such self-assembling structures could be parts of future microscopic mechanical devices. Last year, a team at Harvard University developed similarly self-folding origami figures (SN: 11/25/06, p. 344: Available to subscribers at Chemical Pop-Up Books).

The French team plans to develop more-complicated shapes by cutting the plastic in new ways. “It could be interesting to collaborate with a fashion designer,” Roman says.

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