Toshihiko Arita

Polymer Janus Particles Containing Block-Copolymer Stabilized Magnetic Nanoparticles

In this report, we show a simple route to fabricate Janus particles having magnetic nanoparticles inside them, which can respond and rotate along to magnetic fields. By solvent evaporation from the tetrahydrofran solution of polymer stabilized γ-Fe2O3 nanoparticles, polystyrene (PS), and polyisoprene containing water, aqueous dispersion of Janus microparticles were successfully prepared, and the γ-Fe2O3 nanoparticles were selectively introduced into the PS phase. We demonstrate rotation and accumulation of Janus particles by using a neodymium magnet.

Size exclusion chromatography of quantum dots by utilizing nanoparticle repelling surface of concentrated polymer brush

We have found that the concentrated poly(methyl methacrylate) (PMMA) brush showed the very good nanoparticles (NPs) repellency in its good solvent, e.g. tetrahydrofuran (THF). Whereas the oil- and hydro-phobic (fluorinated), hydrophobic and hydrophilic surfaces adsorbed a lot of NPs. The repellency of NPs did not depend on the surface nature of the NPs. Preparing absorption free columns for size exclusion chromatography (SEC) may enable us to separate quantum dots (QDs) and NPs according to their size. By installing the concentrated PMMA brush into silica monolith columns, we tried to achieve SEC of QDs and NPs. The concentrated PMMA brush immobilized silica monolith columns were prepared by surface initiated atom transfer polymerization of MMA. As a result, we have succeeded in separating QDs according to their size. This SEC system may be advantageous because it can be used in good solvents of the brush regardless of the stability of the surface modifier layer on the NPs.

Localization of polymer-grafted maghemite nanoparticles in a hemisphere of Janus polymer particles prepared by a self-organized precipitation (SORP) method

Microspheric Janus particles with maghemite nanoparticles (NPs) in the hemisphere were investigated. Poly(styrene) (PS)-grafted maghemite NPs were embedded into the PS phase of a PS–poly(isoprene) (PI) Janus polymer particle prepared by a Self-organized Precipitation (SORP) method. The obtained Janus particles showed magnetic field responsive drifts and rotation in water. Potential application in electric paper pixels can be expected from the anisotropic magnetic response of the particle.

Mechanistic study on the synthesis of one-dimensional yttrium aluminum garnet nanostructures under supercritical hydrothermal conditions in the presence of organic amines

Novel one-dimensional nanostructures of yttrium aluminum garnet were synthesized under supercritical hydrothermal conditions in the presence of organic amine molecules. In addition, the effect of different reaction parameters such as the presence of organic amine molecules, pH of the precursor solution, and the state of water (sub- or supercritical conditions) on the morphology of the final product was investigated. In this paper, considering the simultaneous effects of these different parameters, a new electrostatic model is proposed to explain the formation mechanism of the obtained nanostructures.

Supercritical Hydrothermal Synthesis

This chapter describes specific features of a supercritical hydrothermal synthesis method. First, the some characteristic properties of supercritical water are summarized, and then the mechanism of supercritical hydrothermal synthesis is explained. Higher reaction rate and lower solubility are the key factors to synthesize nanosize crystals in a short reaction time. The flow reaction system to achieve rapid heating is explained. Some commercialized process is introduced. This method is useful to synthesize organic molecule modified nanoparticles (NPs). Since the organic molecules and metal–salt aqueous solutions are miscible under the supercritical state, and water molecule works as an acid/base catalyst for the reactions, organic–inorganic conjugate NPs can be synthesized under the condition. The mechanism of the conjugate forming reaction is explained. NPs’ superlattice structure and bioconjugate materials are also formed under the condition. The hybrid NPs show high affinity for the organic solvent or the polymer matrix, which leads to fabricate the organic–inorganic hybrid nanomaterials with the trade-off function (superhybrid nanomaterials). One of the applications is to fabricate a heat-conductive flexible hybrid-polymer sheet. By the surface modification of BN particles by supercritical method, affinity of BN and polymers could be improved so that high BN content of hybrid materials, thus high thermal conductivity materials, could be synthesized.