Direct Coating of Particles by a Liquid Phase Process

This review describes our studies on preparation of core-shell particles with a direct coating technique based on a liquid phase process and their several properties. Various particles were successfully silica-coated with surface modification agents and alkoxide. For Au and Ag nanoparticles, optical spectra of the coated particles agreed with predictions by Mie theory. For metallic Co nanoparticles, crystallization of the Co was promoted with annealing in air with no oxidation of the Co, and the crystallized particles revealed magnetic properties. The silica-coated fluorescence polystyrene microspheres showed more stable fluorescence to laser-irradiation than uncoated microspheres. Besides, silica-coating of AgI, Fe3O4, CoPt and PtRu particles were also successfully performed. Polystyrene and titania could be also used as shell materials. With the use of titania-coated polystyrene particles as precursor, hollow titania spheres could be fabricated by removing polystyrene core from the coated particles with annealing in air. Jingle bell-shaped hollow spheres were fabricated with removal of polystyrene from multilayered particles composed of a silica core, a polystyrene inner shell, and a titania outer shell by immersing them in tetrahydrofuran. Titania-coated silica particles were used for fabrication of colloidal crystals.