Fabrication of colloidal photonic crystal supraparticles via atomization drying for efficient passive cooling†

Colloidal photonic crystals (CPCs), particularly isotropic CPC supraparticles, hold promise for photonic applications. However, the common method for constructing CPC supraparticles heavily relies on the wet self-assembly of colloidal droplets, which limits its scalability. Herein, we achieved a rapid and highly efficient construction of CPC supraparticles using a feasible microfluidic atomization drying assembly strategy. In this process, atomized colloidal droplets were quickly assembled by hot air flow, ensuring the large-scale fabrication of CPC supraparticles. The obtained CPC supraparticles exhibited a robust lattice structure and symmetrical spherical shape. Furthermore, organogel composite CPC films with angle-independent structural colors and excellent stability were developed by co-assembling CPC supraparticles with polydimethylsiloxane gels. Arising from the photonic structure of CPC supraparticles, the organogel composite CPC film selectively reflects solar radiation while maintaining fade-resistant coloration. Additionally, high emission within the atmospheric transparent spectral window (ATSW: 8–13 μm) was induced by the infrared-active functional groups. Therefore, the passive cooling potential of the organogel composite CPC films was explored. A 6 °C temperature drop was achieved for a steel substrate under 1000 W m⁻² simulated solar radiation, significantly broadening its application potential in automotive coatings. The organogel composite CPC film based on CPC supraparticles fabricated in this work provides methodological guidance for CPC design, opening an innovative avenue for passive cooling applications.