Yong Ku Kwon

Core-shell-structured monodisperse copolymer/silica particle suspension and its electrorheological response.

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.

Organic–inorganic hybrid materials for flexible optical waveguide applications

Novel organic–inorganic hybrid materials of 3-acryloxypropyl trimethoxysilane and 4,4′-(hexafluoroisopropylidene)diphenol were synthesized by non-hydrolytic sol–gel processing. Thick, crack-free films were produced by spin-coating without high volume shrinkage during further treatment of the films. The optical properties of the materials were precisely tailored by adjusting the chemical composition of the materials. The tunability of the refractive index allowed us to fabricate step-index optical waveguide structures with well-defined and reproducible refractive index differences to within 0.001. The relatively large, negative thermo–optic coefficients (dn/dT, °C) were obtained in the temperature range below 100 °C and displayed a systematic decrease with the addition of the organic compounds. Using these hybrid materials, we fabricated a flexible optical waveguide based on a soft-lithography technique. The bending loss of a flexible waveguide array was measured and found to yield no significant loss above 2 mm diameter curvature. The transmission performance of each waveguide channel was tested using a 10 Gbps data stream. The electrical output signal from a photodetector, connected to a wide-band oscilloscope, displays a clear 10 Gbps eye pattern.

Polystyrene‐b‐Poly(Ethylene‐r‐butylene)‐b‐Polystyrene Triblock Copolymer/Organoclay Nanocomposites and Their Phase Characteristics

Abstract Intercalated polymer/clay nanocomposites were prepared using a polystyrene‐b‐poly(ethylene‐r‐butylene)‐b‐polystyrene (SEBS) cylindrical triblock copolymer. Dynamic rheological measurements, x‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry analysis (TGA) were conducted to investigate the internal structure and physical and phase characteristics of the nanocomposites. The XRD data confirmed that the interlayer distance between the anisotropic silicates increased due to the intercalation of SEBS into the clay interlayers. As the clay loading increased, the onset points of the order–disorder transition (ODT) and order–order transition (OOT) were found to decrease, whereas the thermal decomposition temperatures, monitored by TGA, increased with the clay loading.

Preparation and characterization of colored electronic ink nanoparticles by high temperature-assisted dyeing for electrophoretic displays.

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.

Synthesis and Characterization of Co-Surfactant Templated Mesoporous Materials with Enhanced Hydrothermal Stability

Ordered mesoporous materials with a hydrothermally-stable, protozeolitic framework were prepared by exploring the direct conversion of inorganic species based on co-surfactant templating systems. To confer hydrothermal stability on the mesoporous materials, the organic-inorganic hybrids were heat-treated in strongly basic media. Co-surfactant templating systems of cetyltrimethylammonium bromide [C16H13(CH3)3NBr, CTAB] with 1,3,5-trimethylbenzene (TMB) or a nonionic block copolymer of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO20PO70EO20) were employed to improve the hydrothermal stability of the organic-inorganic selfassembly during the solid rearrangement process of the inorganic species. The mesoscopic ordering of the pore structure and geometry was identified by X-ray diffraction, small angle neutron scattering and electron microscopy.

Hexagonal to cubic phase transition in the D2O-induced reverse micellar solution of a PEO-b-PPO-b-PEO block copolymer

The morphology of the D2O-induced reverse micellar structure of an amphiphilic block copolymer of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)(EO76PO29EO76) was investigated in hydrophobic media by small angle neutron scattering (SANS). Increasing D2O in the styrene/divinylbenzene solution of EO76PO29EO76 led to a change in morphology of the reverse micelles from a short range ordered molecular aggregate to a hexagonally arranged micelle, and further to a spherical micelle.

Vat Dyeing Properties of a Novel Regenerated Cellulosic Fiber

The dyeing behavior of a novel regenerated cellulosic fiber (enVix®), prepared from secondary cellulose acetate fibers by the hydrolysis of acetyl groups, is investigated with three vat dyes. The effect of liquor ratio, temperature, and dye concentration on the dyeing properties of the enVix and viscose rayon are evaluated. The enVix exhibits better dyeability and fastness than viscose rayon, presumably due to its lower crystallinity.

Preparation of magnetite core-titania shell and hollow titania nanoparticles via layer-by-layer (LbL) assembly method

AbstractTime-resolved small-angle X-ray scattering (SAXS) analysis was performed on a series of poly(ethyleneco-1,4-cyclohexyldimethylene terephthalate)s (PECT copolymers) containing 1.6, 5.3, and 9.8 mol% 1,4-cyclohexyldimethylene (CHDM) units during isothermal crystallization and subsequent melting processes. The measured SAXS data were quantitatively analyzed to yield detailed information (scattering invariant quantity, Q; long period, Lp; lamellar crystal layer thickness, dc; and amorphous layer thickness, da) about the crystal structure evolution and melting devolution behaviors. The Q value was found to be a very sensitive powerful probe for monitoring the crystallization and crystal melting processes. The structural evolution of the copolymers was dominated by the primary crystallization transition. The secondary crystallization effects contributed little to the structural evolution. The few secondary crystals present most likely formed fringed micelle structures that were very small and included a high degree of imperfections. The poor secondary crystal formation was attributed to the presence of bulky, kinked CHDM units, which introduced a high degree of steric hindrance. The high steric hindrance of the CHDM units resulted in their exclusion from the lamellar crystal layers and secondary crystals, and in their insertion into amorphous regions and layers. Overall, the CHDM comonomer units strongly perturbed the crystallization process and the morphological structure of the PECT copolymer. The effects of CHDM as a chemical modifier of poly(ethylene terephthalate)-based polymers may potentially be optimized in an effort to enhance the properties and processability of the polymer.

Morphology and Crystallization in Mixtures of Poly(methyl methacrylate)- Poly(pentafluorostyrene)-Poly(methyl methacrylate) Triblock Copolymer and Poly(vinylidene fluoride)

The microdomain structures and crystallization behavior of the binary blends of poly(methyl methacrylate)-b-poly(pentafluorostyrene)-b-poly(methyl methacrylate) (PMMA-PPFS-PMMA) triblock copolymer with a low molecular weight poly(vinylidene fluoride) (PVDF) were investigated by small-angle X-ray scattering (SAXS), small-angle light scattering (SALS), transmission electron microscopy (TEM), optical microscopy, and differential scanning calorimetry (DSC). A symmetric, PMMA-PPFS-PMMA triblock copolymer with a PPFS weight fraction of 33% was blended with PVDF inN,N-dimethylacetamide (DMAc). In the wide range of PVDF concentration between 10.0 and 30.0 wt%, PVDF was completely incorporated within the PMMA microdomains of PMMAPPFS-PMMA without further phase separation on a micrometer scale. The addition of PVDF altered the phase morphology of PMMA-PPFS-PMMA from well-defined lamellar to disordered. The crystallization of PVDF significantly disturbed the domain structure of PMMA-PPFS-PMMA in the blends, resulting in a poorly-ordered morphology. PVDF displayed unique crystallization behavior as a result of the space constraints imposed by the domain structure of PMMA-PPFS-PMMA. The pre-existing microdomain structures restricted the lamellar orientation and favored a random arrangement of lamellar crystallites.

Facile synthesis of hollow anatase titania prepared by charged polymeric nanosphere template

Two main synthetic routes have been employed to produce inorganic-coated polymer nanoparticles. The first approach is to precipitate to form a thin inorganic shell of hydrolyzed metal oxide precursors onto the polymeric template. The second approach is a layer-by-layer(LBL) deposition technique to form alternate layers of oppositely charged inorganic and organic species on the core materials. Various inorganic materials, including silica, titania, zirconia, clay and iron oxide, are used as a coating material. Among them, titania has attracted a great deal of recent attention, due to their application in catalysis, photovoltaics and photoelectronics. Titaniacoated particles are particularly useful as catalysts, white pigments and electrophoretic particles. These inorganic-coated polymer nanoparticles have been also used to prepare inorganic hollow nanoparticles, which are prepared by removal of the polymer core either by etching in solution or by calcination at high temperature. Hollow titania spheres have been prepared by the LBL manipulation of preformed inorganic nanoparticles onto polymeric colloidal. Recently, templated syntheses of hollow titania spheres was reported based on sulfonated polystyrene particles, which were prepared by seed emulsion polymerization, followed by treatment in concentrated sulfuric acid. We also reported the preparation of hollow titania nanospheres, based on the cationically-charged copolymer core, comprised of styrene, butyl acrylate and cationic [2-(methacryloxy) ethyl]trimethyl ammonium chloride (MOTAC), was prepared by soap-free emulsion polymerization. Cationically-charged polystyrene nanospheres were prepared by using an ionogenic initiator of 2,2’-azo bis(2methylpropionamidine)dihydrochloride (AIBA). The formation of the organic-inorganic hybrids was achieved by adsorption of titania through the hydrolysis of titania precursor. In the present study, to achieve the rapid and sufficient adsorption of inorganic precursor species onto the surfaces of polymer nanospheres, we synthesize positively-charged, monodisperse polymeric cores which are easily associated with negatively-charged inorganic titania precursors by charge density matching. To enhance the charge density of the polymer nanospheres, the polymer cores were prepared by surfactant-free emulsion copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA) and methacryloxyethyltrimethyl ammonium chloride (MOTAC) in the presence of azo bis(isobutylamidine) hydrochloride (AIBA) as an initiator. Unlike our previous study, the component monomers used in the present work are all acrylic, relatively-large amount of the cationic MOTAC monomer can be incorporated within the polymer backbone, which results in the increase in the charge density onto the surface of the polymer core in an attempt to achieve the sufficient adsorption of negatively-charged titania and obtain hollow titania nanospheres with adequate shell thickness.