Raspberry-like nanocomposite microsphere via Double In situ miniemulsion polymerization using interfacial redox initiator system

Abstract

Inorganic/polymer nanocomposites have drawn a lot of attention due to their wide applications in medicine, coating, cosmetics, catalysis, biology, and so on. Many techniques have been adopted to the fabrication and morphology control of nanocomposite particles, such as aqueous dispersion polymerization, surfactant free polymerization, heterophase polymerization, Pickering emulsion polymerization, miniemulsion polymerization, and so forth. Such nanocomposite microspheres have been examined in a wide range of applications, ranging from new synthetic mimics for understanding the behavior of micro-meteorites, to stimulus responsive Pickering emulsifiers to tough, transparent, scratch-resistant coatings for either timber or housing exteriors. However, to control the dispersion of nanoparticles into polymer matrices is a significant challenge and it is often difficult to achieve this goal as inorganic particles are typically immiscible with polymer phase. Among the above methods miniemulsion polymerization has been proved to be a powerful and versatile process in the fabrication of inorganic/polymer microspheres. However, colloidal nanocomposite microspheres are most synthesized by in situ the polymerization of organic monomer in the presence of pre-formed inorganic colloidal particles. In order to obtain high encapsulation efficiencies, the silica particles had to be well dispersed within the monomer phase prior to miniemulsification. The most difficulty in the preparation of nanocomposites is to avoid the aggregation of nanoparticles in the polymer matrix. According to Steven P. Armes’ opinion, raspberry-like nanocomposite microspheres satisfy the basic demands. That is, the nanoparticles not only closely pack on the surface of polymer microspheres, but distribute homogeneously throughout the polymer microspheres. In order to obtain raspberry-like microspheres, auxiliary monomers were required to enhance the interaction between hydroxyl groups (acidic) on silica surfaces and amino groups (basic) during the formation of nanocomposite particles. 4-Vinylpyridine (4-VP), 1-vinylimidazole (1-VID), and 2-(methacryloyl) ethyltrimethylammonium chloride (MTC) have been used to successfully prepare PMMA/SiO2 organic-inorganic microspheres. Following the above synthesis route, Armes prepared a series of conducting polymer-silica nanocomposite microspheres based on either polyaniline, polypyrrole or poly(3,4-ethylenedioxythiophene). Stefan A. F. Bon prepared armored nanocomposite polymer microspheres by soap-free emulsion polymerizations in the presence of silica nanoparticles. Furthermore more complex multilayered nanocomposite polymer colloids were obtained by using a second conventional seeded emulsion polymerization step. Based on our previous works, silica/polymer hybrid particles have been fabricated successfully via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Inspired by these interesting and valuable results, we investigated the feasibility of fabrication of nanocomposite microspheres with nanosilica distributing homogeneously throughout the polymer microspheres. Herein we report a novel and flexible technique to fabricate raspberry-like silica/polystyrene microspheres via interfacial initiated miniemulsion polymerization. The nanocompostite microspheres were fabricated via double in situ miniemulsion polymerization by taking full advantage of phase separation between inorganic component and the growing polymer. Nanosilica particles are formed throughout the polymer microspheres. This method can be expected to produce large quantity of submicrometer sized nanocomposite microspheres with high silica content towards biomimetic nanocomposites.