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Photonic crystals made by dehydrating hydrogels
Hydrogel nanoparticles can be made to give up some of their water content easily and controllably. Researchers have taken advantage of that property to design a family of photonic crystals that one day may be used in telecommunications or other optoelectronic applications. Photonic materials are endowed with optical properties that can be used to control the flow of light just as electronic materials are used to control the flow of electrons. To make the specimens, researchers synthesize nanoparticles from N-isopropylacrylamide that has been lightly cross-linked with N,N-methylenebisacrylamide. The colorful, glassy product is heated (annealed), causing the hydrogel to lose some of its water and to become disordered. After removing small amounts of water from the solution, the researchers cool the remainder, causing the particles to reabsorb water and crystallize. By annealing the material repeatedly, the scientists can fine-tune its optical properties--leading to a large group of photonic crystals (examples shown). Because the materials are made from polymers, they can be handled with common processing techniques, such as casting, molding, and spin coating.
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