Wettability Controllable Structural Color Films with High Stability for Invisible Coding

Colloidal photonic crystals (CPCs) have attracted significant interest due to their periodic crystalline structure and potential applications in prints, displays, and security devices. However, the improvement of color durability to meet the requirements in diverse applications remains a challenge. Herein, we demonstrated wettability controllable CPCs through an efficient and convenient approach. The microspheres composing of hard cores and soft shells, were fabricated by seed-emulsion polymerization and assembled into colloidal crystal films by bar-coating method. Upon postprocessing treatment by heating, the wettability of the CPC films transitioned from hydrophilicity to hydrophobicity, facilitated by surface group migration. Heat treatment promoted the soft shell melting, leading to a more compact microsphere arrangement and improved color stability. Meanwhile, by taking advantage of the programmable wettability of CPC films, we achieved color-based anti-invisible structural colors, showcasing their potential for anticounterfeiting and identification purposes.