Colorful humidity sensitive photonic crystal hydrogel

A colorful humidity sensitive photonic crystal (PC) hydrogel was facilely fabricated by infiltrating acrylamide (AAm) solution into a P(St–MMA–AA) PC template and subsequently photo-polymerizing. The color of the samples was sensitive to humidity; it could reversibly vary from transparent to violet, blue, cyan, green and red under various humidity conditions, covering the whole visible range. This could be attributed to the humidity sensitivity of the sample's stopband, with a maximum change of 240 nm resulting from the varying humidity. Furthermore, the color response showed good stability under cyclic humidity experiments. As-prepared PAAm–P(St–MMA–AA) PC hydrogel successfully combined the humidity sensitivity of PAAm and structure color of the PC template, which suggested a promising composite material as an economical alternative to traditional humidity sensors, and also provided a new insight into the design and development of novel composite functional materials based on a PC template.