(38a) Design of Nano/Micro Structures of Hollow, Skeletal, and Porous Particles

Hollow silica nanoparticles exhibit unique properties such as thermal insulation, transparency, light diffusion, and so on which are derived from hollow interior surrounded by a silica shell. In order to improve these properties more, control of the silica shell structure in micro- and macro-level is important. The hollow nanoparticles are mainly prepared by template method, in which silica coating is performed on the solid or soft template surface and then the template is removed by chemical etching. Previously, gas adsorption analysis indicated that micro-pores (<2 nm) existed in the silica shell where molecules can pass through. Using the structure, selective deposition of tin oxide nanoparticles inside or outside the silica shell has been achieved. In addition, apparent density of the silica shell can be controlled between 1.45 and 2.20 g/cm^3 by adjustment of sol-gel conditions. The low apparent density of the silica shell significantly improved thermal insulation ability of the hollow nanoparticle /polyurethane film. While, macro-sized pores were also produced on the cubic shaped silica shell, by use of polarity difference in the reaction system. The skeletal silica nanoparticles have mostly hollow which divided by 12 silica nanoframes and are expected to protect organic substance (e.g., phosphor) from external stimuli. How to control micro- to macro-structures of hollow silica nanoparticles and how these functionalities have been achieved are discussed.