Synthesis of hollow inorganic nano-particles templated by polymeric micelles with core-shell-corona structure and their applications

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We tried to synthesize inorganic hollow nano-particles by templating a polymeric micelle with a core-shell-corona structure in aqueous solutions. We started with silica nano-particles. The template micelle was prepared from poly (styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO), and the precursor employed is tetramethoxysilane (TMOS). Silica was deposited in a domain of PVP shell by sol-gel reaction. After removing the template polymer from the polymer-silica hybrid particles by calcinations, we obtained hollow silica nanoparticles. The obtained hollow silica nanoparticles were found to have a spherical structure with narrow distributions of void volume and shell thickness.Furthermore, we tried to control the structural parameters of the hollow silica; i.e., the void volumes by changing the PS chain length, and the wall thickness by changing the amount of the silica precursor. As expected, the void volume of the obtained hollow silica regularly increased with the increase in the PS chain length, and the wall thickness increased with the increase in the concentration of the precursor. To the best of our knowledge, this is the first study in which the cavity size and wall thickness of the hollow silica were successfully fine-tuned on a scale of several nanometers.The significant feature of our method is that each block of the copolymer has its own function during the silica synthesis ; (i) the PS block forms the core of the micelle to be a template of the void space in the hollow silica, (ii) the PVP block forms the shell to be a reaction field of the sol-gel reaction of TMOS, and (iii) PEO forms the corona to stabilize the polymer/silica intermediate hybrids.Our method seems to be a comprehensive one; that is, it can be applied to the other inorganic materials and different triblock copolymer micelles can be used as a template.