Synthesis of PS@SiO₂ Microsphere and Optical Properties of Its Three-Dimensional Photonic Crystals

By coating vinyl-modified silicon (Vi-SiO₂) shell on the surface of polystyrene (PS) microspheres in alkaline medium, PS@SiO₂ microspheres were synthesized using vinyltriethoxysilane (VTES) as silicon source. Subsequently, PS@SiO₂ three-dimensional (3D) photonic crystals were prepared by rod-coating method and their optical properties were investigated. The synthesized PS microspheres and PS@SiO₂ microspheres were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectroscopy. Results showed that the stretching vibration absorption peaks of Si―O―Si at 1155 cm⁻¹ and 1044 cm⁻¹ in the infrared spectra proved the synthesis of Vi-SiO₂. The PS@SiO₂ microspheres had an obvious core-shell structure, with a Vi-SiO₂ shell thickness of about 20 nm. At the same time, Vi-SiO₂ formed a uniform and smooth shell on the surface of PS microspheres. Importantly, the coating of Vi-SiO₂ had no significant effect on the monodispersity and sphericity of PS microspheres. The synthesized PS@SiO₂ microspheres had particle sizes of 211, 230, 251 nm, and 270 nm, respectively. The cores of PS@SiO₂ microspheres were PS microspheres with particle sizes of 177, 197, 218 nm, and 240 nm, respectively. Photonic crystals assembled from PS@SiO₂ microspheres of four different particle sizes exhibited blue, green, yellow, and red structural colors, respectively, and the corresponding reflectance spectra showed reflection peaks at 475, 525, 575 nm, and 650 nm, respectively. Meanwhile, SEM images of photonic crystals assembled from PS@SiO₂ microspheres of four different particle sizes all proved that PS@SiO₂ photonic crystals had a regular face-centered cubic structure. In addition, PS@SiO₂ photonic crystals displayed different structural colors at different viewing angles, meaning that they possessed iridescent effects.