In a recent paper, we describe a method to design 3D shapes through the controlled growth of a thin polymer sheet. The method relies on a polymer film whose internal chemistry, and consequently its response to stimuli, is altered by shining ultraviolet light (UV) through a mask. The polymer film swells like a sponge in water, but will swell less where UV light has shined through the holes in the mask and more where it has not. The high swelling regions then buckle to accommodate the extra material. To make the technique useful to control the 3D shape, we borrow a technique from printing, “half-toning,” in which a pattern of low swelling dots are embedded in a high swelling background. By changing the local size of the dots, we can achieve a very fine-tuned control over the local degree of swelling.
J. Kim, J.A. Hanna, M. Byun, C.D. Santangelo, and R.C. Hayward, “Designing responsive buckled surfaces by halftone gel lithography,” Science 335, 1201-1205 (2012). [JOURNAL].
We also studied a similar material system with in-plane swelling, the “bistrip”, in another article in the journal Soft Matter. There, a strip of high swelling is attached to a strip of low swelling material along their long edges. Surprisingly, the result rolls up to a radius that scales with the thickness of the strip to the 2/3 power.
J. Kim, J.A. Hanna, R.C. Hayward, and C.D. Santangelo, “Thermally responsive rolling of thin gel strips with discrete variations in swelling,” Soft Matter 8, 2375-2381 (2012). [JOURNAL].