Facile fabrication of tunable colloidal photonic crystal hydrogel supraballs toward a colorimetric humidity sensor

We report an alternative pathway for the facile fabrication of tunable colloidal photonic crystal (TCPC) hydrogel supraballs via a simple microfluidic device for the first time. The TCPC hydrogel supraballs immobilized the CPC structure into a PAm hydrogel, which has properties suitable for humidity sensing and volume phase transition behavior. Thus, the as-prepared TCPC hydrogel supraballs can monitor a very broad humidity range by obvious color changes rather than traditional volume changes suffering from a time-consuming gravimetric measurement. The color changes are reversible and durable corresponding to humidity sensitivity, and cover almost the whole visible spectrum. More interestingly, the optical stopband of the spherical TCPCs is angle-independent on the curved surface. Furthermore, this procedure also provides a new insight into the creation of novel micro-scaled stimuli-responsive CPC devices.