Preferential self-assembly behavior of polydisperse silica particles under negative pressure

The research about assembly behavior of colloidal particles under external field is a key of improved self-assembly method. Although high quality photonic crystals prepared by improved self-assembly method under external field have been reported, real applications require monodisperse particles. Here, we designed negative pressure field to prepare opal film composed of polydisperse SiO₂ particles. The effect of different negative pressures on the opal's surface morphology and photonic band gap (PBG) properties was investigated. Under the optimal pressure, close-packed opal was obtained, which is composed of irregular and polydisperse silica particles. We attribute this to the balance between sedimentation of SiO₂ particles and solvent evaporation during the assembly process. Importantly, this approach could be complementary to the preparing of three-dimensional photonic crystals with long-range ordered structures in usual laboratory.