(88c) Preparation and Assembly of Anisotropically Polymer-Grafted Silica Nanospheres Via Adsorption On Charged Surface

Anisotropic particles that possess non-uniformity in surface structure or function have attracted great attention.  Owing to the anisotropy in their inter-particle interaction, these particles are expected to become an important element of functional nanomaterials if they can be assembled into useful structures. However, up until now, the preparation of anisotropic particles less than 100 nm in diameter has been a difficult challenge. In this study, a method to synthesize anisotropically polymer-grafted silica nanospheres was developed by utilizing their adsorption to a charged surface. First, Carboxyl-terminated polystyrene (Mw = 37800) was synthesized via atom transfer radical polymerization (ATRP). Next, spherical silica nanospheres (SNSs) 50 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 since the surface of SNSs is negatively-charged while that of HT is positively-charged. Next, SNSs-adsorbing HT were treated with 3-aminopropyltriethoxysilane to introduce amino groups on the exposed surface of the SNSs. Coupling reaction between amino group on SNSs surface and carboxyl-terminated polystyrene was carried out at room temperature using coupling agents (DCC and DMAP). HT substrates were removed by being dissolved in acidic water to give anisotropically polymer-grafted SNSs. Mixture of these particles, water and chloroform was emulsified to formed water-in-oil microemulsion where polymer-grafted SNSs are located at the water-oil interface. Carefully removing the liquid phase produced hollow particles of several hundred nm in size with their wall constructed from polymer-grafted SNSs.