Origami the Easy Way

Capillary Origami: Spontaneous Wrapping of a Droplet with an Elastic Sheet

Charlotte Py, Paul Reverdy, Lionel Doppler, Jose Bico, Benoit Roman, and Charles N. Baroud

PRL 98, 156103 (2007)

URL: http://link.aps.org/abstract/PRL/v98/e156103

This article contains some of the pest pictures I've seen in a PRL article.

The authors place little sheets of polydimethylsiloxane (PDMS) on a hydrophobic surface and add a drop of water. As the water evaporates, the sheets fold up. The shape and thickness of the sheet determine what the final object will be. In this type of origami, Nature does the work for you. Like the chia pet, "Just add water!" (Of course, I am sure the authors invested a considerable amount of labor before they added the water and let Nature take over.)

The pictures on the first page show the folding of a square into a tube and a triangle into a tetrahedron. On the final page, the authors show of the expertise of their lab by folding a flower into a sphere, a cross into a cube, and a square with two rounded corners into a triangle with a tube at the bottom.

The theoretical explanation in this paper is excellent. If I had to summarize their entire theory of folding in one word, it would be "competition." Competition between bending energy and surface tension sets the fundamental length scale and determines the shape of the liquid-membrane interface. Competition between bending energy and stretching energy determines whether a sheet will bend or crumple. The authors explain these ideas and their model clearly.

This paper demonstrates a good balance between experiment and theory. Two-dimensional membranes are an interesting topic, because the systems are simple enough that analytic models can be derived and solved. However, new effects are reported frequently. Although the field has been around for hundreds of years, it continues to be a fertile area for research.