Rotating 1-D magnetic photonic crystal balls with a tunable lattice constant.

The responsive photonic crystal (RPC) balls with adjustable lattice constant and controllable rotation developed to date are all based on Janus particles of three dimensional (3-D) periodical structures, which suffer from color uneveness and asymmetric volume change, limiting the applications in the fields of encoding, sensing and displays. In this study, we have developed the first 1-D magnetic photonic crystal balls with tunable lattice constants by fixing collectively oriented periodical 1-D magnetic nanochain-like structures in responsive polymer poly(N-isopropylacrylamide) hydrogel balls under magnetic field (H) and UV irradiation. The structural colors of the balls are uniform on the entire ball and can be regulated by temperature (T) and solvents. The as-prepared RPC balls always retain a perfectly spherical shape even when the hydrogel volume changes with stimuli because of the low content of the included 1-D magnetic nanochain-like structures. This endows smooth rotation in the H direction to switch "on/off" their structural colors at various stimuli, as demonstrated by a colorful display application at temperature ranging from 10 to 35 °C. The as-developed RPC balls are expected to have promising potential applications in color display, rewritable signage, biological and chemical sensors owing to their excellent multi-response properties.