Co-deposition motif for constructing inverse opal photonic crystals with pH sensing

Polyacrylamide (PAM) hydrogel photonic crystals with an inverse opal structure were elaborated using a modified vertical deposition approach involving a co-deposition motif. Free-standing inverse opal hydrogel (IOH) films of different thicknesses that could be peeled from the support were first fabricated. A three-dimensional ordered structure without over-layers could easily be acquired by the co-deposition approach. Moreover, the bi-continuous structure was not affected by the increase in film thickness. All these IOH films showed a fascinating pH response property after hydrolysis, and the color change corresponding to the shift of the Bragg diffraction peak of the acquired hydrogel photonic crystal films could be easily distinguished by the naked eye. Three types of IOH films with different thicknesses showed similar pH response properties. The co-deposition approach is found to be suitable for the construction of thicker IOH film without over-layers.