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Aoba Ku, Japan

Okada A.,6 6 07 Aoba | Nagao D.,6 6 07 Aoba | Ishii H.,6 6 07 Aoba | Konno M.,6 6 07 Aoba
Soft Matter

Micron-sized silica rattle particles were directly observed in aqueous media with an optical microscope to demonstrate the movability of inner silica spheres within the compartment of the silica shell. The rattle particles were prepared by a combined method of fabricating multilayered particles (silica sphere/polystyrene (PSt) inner shell/silica outer shell) and removing the polymer component in the multilayered particles. The polymer component of PSt was removed by heating the multilayered particles at 500 °C for 4 h, which resulted in a successful preparation of silica rattle particles without any residual polymer component. The silica rattle particles in the presence of polyvinylpyrrolidone used as a viscosity enhancer were observed with the optical microscope under an alternating electric field, revealing that less than 10% of inner spheres in the pearl chain of rattle particles could be randomly moved in the compartment of the silica shell. For increasing the percentage of inner spheres randomly moving, the silica rattle particles were slightly etched with a diluted NaOH solution to detach the inner spheres from the inside wall of the silica shell. The slight etching of the silica component led to the observation of approximately 75% inner spheres randomly moving under the applied electric field. This is the first direct observation to show that the single spheres incorporated in the shell compartment are capable to freely move without sticking to the inside wall of the shell. © The Royal Society of Chemistry 2012. Source

Nishi M.,6 6 07 Aoba | Nagao D.,6 6 07 Aoba | Hayasaka K.,6 6 07 Aoba | Ishii H.,6 6 07 Aoba | Konno M.,6 6 07 Aoba
Soft Matter

Magnetoresponsive, anisotropic composite particles were prepared to explore a new type of building blocks reversibly changing their chain lengths by switching on an external magnetic field. The composite particles were synthesized with three-step polymerization comprising (i) polymerization to coat magnetoresponsive silica particles with crosslinked poly(methyl methacrylate) (PMMA), (ii) polymerization to form a polystyrene (PSt) lobe on the PMMA-coated particles and (iii) polymerization to form another PSt lobe on the opposite side of the former lobe. The structure of the composite particles was analyzed with scanning transmission electron microscopy showing rod-like polymer particles incorporating a magnetoresponsive particle in the middle of a rod-like particle. The composite particles suspended in aqueous solution of polyvinylpyrrolidone used as a viscosity enhancer were observed by optical microscopy under applied external fields. Application of an alternating electric field at a high frequency of 2 MHz oriented the rod-like particles parallel to the electric field and assembled them to form pearl-chain structures of the composite particles. The chain lengths of the oriented rod-like particles were extended during the application of the electric field. While applying the electric field, an additional application of magnetic field with a field strength of 100 mT changed the chain structure so as to allow the magnetoresponsive parts to come close to each other. A combined application in which the magnetic field was switched on and off intermittently under a fixed electric field could reversibly compress and extend the particle chains and control their chain lengths. © 2012 The Royal Society of Chemistry. Source

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