RESUMEN

A new approach for synthesizing well-defined hollow nanochanneled-silica nanosphere particles is demonstrated, and the structural details of these particles are described for the first time. Positively charged styrene copolymer nanospheres with a clean, smooth surface and a very narrow size distribution are synthesized by surfactant-free emulsion copolymerization and used as a thermal sacrificial core template for the production of core-shell nanoparticles. A surfactant/silica composite shell with a uniform thickness is successfully produced and deposited onto the polymeric core template by charge density matching between the polymer nanosphere template surface and the negatively charged silica precursors and then followed by selective thermal decomposition of the polymeric core and the surfactant cylinder domains in the shell, producing the hollow nanochanneled-silica nanospheres. Comprehensive, quantitative structural analyses collectively confirm that the obtained nanoparticles are structurally well defined with a hollow core and a shell composed of cylindrical nanochannels that provide facile accessibility to the hollow interior space. Overall, the hollow nanochanneled-silica nanoparticles have great potential for applications in various fields.

RESUMEN

Monodisperse core-shell-structured poly(styrene-co-butyl acrylate-co-[2-(methacryloxy)ethyl] trimethylammonium chloride)/silica (PSBM/SiO2) nanoparticles were applied as new electrorheological (ER) materials in which the particles were dispersed in an insulating oil. These nanoparticles were prepared by the consecutive precipitation of cetyltrimethylammonium bromide and negatively charged tetraethylorthosilicate onto the cationic surfaces of PSBM colloidal particles. The successful deposition of the shell phase of the particles and their morphology was examined by transmission and scanning electron microscopy. Their ER properties were studied with a rotational rheometer under different shear modes: controlled shear rate, steady shear under constant shear rate, and creep test. The silica shell allowed the PSBM/SiO2 particles to exhibit typical ER performance under an applied electric field. The dielectric spectra of the PSBM/SiO2-based ER fluid were also recorded using an LCR meter, which was correlated to the ER performance of the ER fluid.

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RESUMEN

We theoretically consider the commensurability problem of AB diblock lamellar phase confined between parallel plates, in cylinder, and in sphere calculating the free energy of confined lamellar phase which is generalized in terms of dimensionality of confinement (d) and conformational asymmetry (ɛ). We find that the first-order layer-addition transition of lamellar layers parallel to the confining surface (L(∥)) becomes suppressed as the dimensionality of confinement increases. For lamellae confined in curved space, the conformational asymmetry alters the location of layer-addition transition point and the stability of L(∥) against nonconcentric layers. When the surface-preferential block becomes flexible, the radius of cylindrically or spherically confined space at the layer-addition transition, where the number of A-B layers of L(∥) changes from l layers to l+1 layers, increases if l is odd and decreases otherwise due to the tendency of less flexible block filling innermost layer. The curved space also weakens the stability L(∥) competing with nonconcentric layers when the surface-preferential block becomes less flexible. The phase maps in the parameter space of conformational asymmetry and degree of confinement are constructed for different cases of the confinement dimensionality and the surface fields, demonstrating the effects of various system variables on the confined lamellar structures.

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Titania-coated polymeric nanoparticles were synthesized based on the cationic colloidal particles which were prepared by surfactant-free emulsion copolymerization of styrene and butylacrylate in the presence of a cationic monomer, methacryloxyethyltrimethyl ammonium chloride (MOTAC) using azobis(isobutylamidine)hydrochloride (AIBA) as an initiator. These cationic particles were stabilized by poly(vinylpyrrolidone) (PVP). Then, these particles were dispersed in ethanol and mixed with titanium(IV) butoxide. Negatively charged titania precursors were rapidly hydrolyzed onto the cationic surfaces of colloidal particles. Subsequently, the samples were heated to 450 degrees C to form anatase TiO2 and to remove the colloidal template, which resulted in hollow nanospheres. The hollow titania particles were characterized with zeta analyzer, transmission electron microscopy, scanning electron microscopy, light scattering, X-ray diffraction, thermogravimetric analysis and FT-IR.

RESUMEN

An amphiphilic star block copolymer of poly(L-lactic acid)-b-poly(ethylene glycol) (PLLA-b-PEG) was synthesized using a hexachlorocyclotriphosphazene ring (N3P3Cl6) as a core. N3P3(OC6H4-p-CHO)6 was prepared by the reaction between the hexachlorocyclotriphosphazene core and 4-hydroxybenzaldehyde sodium salt. N3P3(OC6H4-p-CH2OH)6 was then obtained by reduction of N3P3(OC6H4-p-CHO)6. N3P3(OC6H4-p-CH2OH)6 was used as an initiator to obtain a PLLA-grafted star branched polymer by polymerizing lactide, which was then treated with succinic acid to produce a carboxylated PLLA-grafted star polymer. PEG blocks were attached to a carboxylated PLLA-grafted star polymer to produce an amphiphilic PLLA-b-PEG-grafted star block polymer by additional esterification with poly(ethylene glycol methyl ether).

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RESUMEN

The charged polymer nanoparticles of poly(methyl methacrylate-co-ethylene glycol dimethacrylate) were prepared by emulsifier-free emulsion copolymerization and aminolysis. Coloring on the nanoparticles was achieved by high temperature-assisted disperse dyeing. In the presence of a charge control and stabilizing agent, the colored PMMA nanoparticles showed the electrophoretic mobility because of the amine groups on their surfaces. The morphology and material characteristics of the colored polymeric nanospheres were also investigated.

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