(524e) Larger-Scale Production of Janus Silica-On-Silica Nanoparticles Via Adsorption On Charged Surface

Recently, Janus particles whose surface structure or function differs between two sides of the particles have attracted great attention. Owing to the anisotropy in their structure and properties, these particles are expected to become an important element of functional nanomaterials if they can be assembled into useful structures. However, the preparation of anisotropic particles less than 100 nm in diameter has been a difficult challenge. To make these particles practical, they should be produced in large scale. In this study, a simple method to synthesize Janus nanoparticles in large quantity by utilizing their adsorption onto a charged surface is demonstrated. First, spherical silica nanospheres (SNSs) less than 100 nm in diameterwere mixed together with hydrotalcite (HT), a plate-like layered crystals,in water at pH 11.5. Under this pH condition, SNSs are adsorbed on the surface of HT by electrostatic interaction because the surface of SNSs is negatively-charged while that of HT is positively-charged. Next, the exposed surfaces in the immobilized particles are modified with aminopropylsilanes so that electrostatic adsorption of additional silica nanospheres can be operative. Finally, HT substrates were removed by being dissolved in acidic water to give anisotropically surface-modified SNSs. Gram-scale synthesis of Janus particles can be achieved by this approach.