Microdroplets confined assembly of opal composites in dynamic borate ester-based networks

Although materials with structural colours are known to be resistant to photobleaching, the damage caused by structural failure and lack of suitable fabrication methods limit their practical uses. Herein, confinement-mediated self-assembly of colloidal crystals in dynamic borate ester-based networks is demonstrated to produce spherical opal composites using a microfluidic device. The resulting optical beads are flowable and injectable, facilitating injection moulding of three-dimensionally well-defined macroscopic opals. Further, the opal composites formed in semi-spherical sessile microdroplets can serve as individual pixels for two-dimensional patterns integrating angle-independent structural colours and self-healing characteristics. These findings provide novel insights for the development of multi-scale opal constructs with ability to resist the physical damage and to increase the lifetime.