Encoding complex wettability patterns in chemically functionalized 3D photonic crystals.

Much of modern technology--from data encryption to environmental sensors to templates for device fabrication--relies on encoding complex chemical information in a single material platform. Here we develop a technique for patterning multiple chemical functionalities throughout the inner surfaces of three-dimensional (3D) porous structures. Using a highly ordered 3D photonic crystal as a regionally functionalized porous carrier, we generate complex wettability patterns. Immersion of the sample in a particular fluid induces its localized infiltration and disappearance of the bright color in a unique spatial pattern dictated by the surface chemistry. We use this platform to illustrate multilevel message encryption, with selective decoding by specific solvents. Due to the highly symmetric geometry of inverse opal photonic crystals used as carriers, a remarkable selectivity of wetting is observed over a very broad range of fluids' surface tensions. These properties, combined with the easily detectable optical response, suggest that such a system could also find use as a colorimetric indicator for liquids based on wettability.