Engineering particles towards 3D supraballs-based passive cooling via grafting CDs onto colloidal photonic crystals

Particle engineering has opened the floodgates to material science in both fundamental and application field. However, covalent interactions have not yet been adequately designed in the particle engineering for functional colloidal photonic crystals (CPCs). Herein, we achieved covalent coupling between carboxyl-rich poly(styrene-acrylic acid) (P(St-AA)) monodispersed colloidal particles and amine-rich carbon dots (CDs) based on an feasible and universal particle engineering strategy. The designed CDs-grafted P(St-AA) monodispersed colloidal particles initiate a hydrogen bond-driven assembly mode and ensure the construction of large-scale crack-free CPCs. Moreover, the CDs equipped with selective broad-band absorption capacity could improve the saturation of structural colors for high-visibility CPCs. Furthermore, an injectable photonic hydrogel (IPH) is developed to design CPC supraball hydrogel via integrating the CDs-grafted P(St-AA) CPC supraballs with supramolecular hydrogel. Combining superior flexibility, sufficient self-healing capacity of supramolecular hydrogel with visual optical information of our CPC supraballs, a cyclically reversible coding and decoding system was developed. Meanwhile, we firstly demonstrated the novel strategy of 3D supraballs-based passive cooling. The designed 3D CPC supraball hydrogel presents nearly full observation angle reflections behavior and excellent water evaporation capacity and achieves 3.6 °C temperature drops, showing the application advantages in 3D thermal management. This work not only provides a new insight for manipulating optical properties of CPCs, but also demonstrates an easy-to-perform platform, as well as indicates the direction for the promising application of CPCs.