Multiresponsive hydrogel photonic crystal microparticles with inverse-opal structure.

Hydrogel photonic crystal microparticles (HPCMs) with inverse-opal structure are generated through a combination of microfluidic and templating technique. Temperature and pH responsive HPCMs have firstly been prepared by copolymerizing functional monomers, for example, N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA). HPCMs not only show tunable color variation almost covering the entire wavelength of visible light (above 150 nm of stop-band shift) by simply tailoring temperature or pH value of the solution, but also display rapid response (less than 1 min) due to the small volume and well-ordered porous structure. Importantly, the temperature sensing window of the HPCMs can be enlarged by controlling the transition temperature of the hydrogel matrix, and the HPCMs also exhibit good reversibility and reproducibility for pH response. Moreover, functional species or particles (such as azobenzene derivative or magnetic nanoparticles) can be further introduced into the hydrogel matrix by using post-treatment process. These functionalized HPCMs can respond to the UV/visible light without significantly influencing the temperature and pH response, and thus, multiresponsive capability within one single particle can be realized. The presence of magnetic nanoparticles may facilitate secondary assembly, which has potential applications in advanced optical devices.