title: Preparation of asymmetrically nanoparticle-supported, monodisperse composite dumbbells by protruding a smooth polymer bulge from rugged spheres.
abstract: A novel method is proposed to create asymmetrically nanoparticle-supported, monodisperse composite dumbbells. The method consists of the three steps of double soap-free emulsion polymerizations before and after a heterocoagulation. In the first step, soap-free emulsion polymerization was conducted to cover silica cores with cross-linked poly(methyl methacrylate) (PMMA) shells. Then, positively or negatively charged silica nanoparticles were heterocoagulated with the silica-PMMA core-shell particles. In the heterocoagulations, the nanoparticles surface-modified with a cationic silane coupling agent, 3-aminopropyltriethoxysilane, were used as the positively charged ones, and silica nanoparticles without any treatment were used as the negatively charged ones. In the third step, soap-free polymerizations at different pH values were performed to protrude a polystyrene (PSt) bulge from the core-shell particles supporting the charged silica nanoparticles. In the polymerization, the core-shell particles heterocoagulated with the positively charged silica nanoparticles were aggregated in an acidic condition whereas the silica nanoparticles supported on the core-shell particles were dissolved in a basic condition. For the negatively charged silica nanoparticle, a PSt bulge was successfully protruded from the core-shell particle in acidic and neutral conditions without aggregation of the core-shell particles. The protrusion of the PSt bulge became distinctive when the number of heterocoagulated silica nanoparticles per core-shell particle was increased. Additional heterocoagulation experiments, in which positively or negatively charged magnetite nanoparticles were mixed with the asymmetrically nanoparticle-supported composite dumbbells, confirmed direct exposure of silica nanoparticles to the outer solvent phase.
authors.affiliation: Department of Chemical Engineering, Graduate School of Engineering, Tohoku University, 6-6-07 Aoba, Aramaki-aza Aoba-ku, Sendai 980-8579, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Nagao
authors.forename: Kanako
authors.initials: K
authors.lastname: Goto
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Ishii
authors.forename: Mikio
authors.initials: M
authors.lastname: Konno