Preparation of structurally colored films assembled by using polystyrene@silica, air@silica and air@carbon@silica core–shell nanoparticles with enhanced color visibility

Abstract

Polystyrene@silica (PS@SiO₂) core–shell nanospheres were synthesized using a surfactant free method followed by a modified Stöber method in the research reported in this paper. Hollow SiO₂ was obtained by calcining the PS@SiO₂ core–shell nanoparticles (NPs) at 500 °C in air and air@C@SiO₂ (where C represents carbon) was prepared by calcining PS@SiO₂ in argon (Ar). Scanning electron microscopy and transmission electron microscopy were used to confirm the formation of a homogeneous SiO₂ shell on the negatively charged PS beads. Energy dispersive X-ray spectroscopy element mapping was utilized to confirm the existence and homogeneity of the C layer in the air@C@SiO₂ nanospheres. After calcination, C partly remained inside the SiO₂ shell and functioned as an absorbent material. The advantages of using negatively charged PS beads to prepare PS@SiO₂ core–shell NPs and calcination of PS@SiO₂ in Ar to prepare hollow SiO₂ are: (1) the lower cost compared with the positively charged PS beads, because the negatively charged PS beads could be obtained by using cheap anionic initiators (such as potassium persulfate); (2) the color saturation of the photonic crystals (PCs) composed from hollow SiO₂ is significantly enhanced without disturbing the PCs arrays when the calcination process is carried out in Ar. Hollow SiO₂ PCs with enhanced color saturation will enrich the application of core–shell structures in many fields such as bionic colors, paintings, cosmetics, and photonic papers.