Kyung-Do Suh

Zinc oxide/polymethylmethacrylate composite microspheres by in situ suspension polymerization and their morphological study

Homogenously zinc oxide (ZnO)-dispersed polymethylmethacrylate (PMMA) composite microspheres were produced considering the interfacial characteristics of ZnO and PMMA in in situ suspension polymerization. The morphological observation with electron microscopes revealed that nano-sized ZnO particles were embedded homogeneously in the inner part of PMMA microspheres. Moreover, their spherical shape could be maintained to a large amount of ZnO in the PMMA phase. From this study, it was found that one of key requirements in the synthesis of inorganic/polymer composite microspheres was the enhanced interfacial compatibility between inorganic and polymer, which was achieved by treating the surface of inorganics hydrophobically and imparting conformational anchorage factor at inorganic interfaces.

Monodisperse micron-sized polystyrene particles by seeded polymerization : effect of seed crosslinking on monomer swelling and particle morphology

Monodisperse micron-sized polystyrene particles were produced by seeded polymerization, and the effect of seed crosslinking on styrene monomer swelling and final particle morphology were considered. The monomer swelling procedure using crosslinked seed particles was predicted with a thermodynamic equation. Employing this equation, the crosslinking density of the seed particles could be determined from the rate of transport of the monomer molecules to the crosslinked seed particles. From a thermodynamic viewpoint, it was elucidated that the monomer swelling procedure was strongly dependent on the seed crosslinking density. Therefore, for an effective swelling of the monomer, an optimum seed crosslinking density was required. After polymerization of these swollen particles, highly monodisperse polystyrene particles could be obtained with a size range of over 10 μm.

Preparation of polymer‐dispersed liquid crystal films containing a small amount of liquid crystalline polymer and their properties

Polymer-dispersed liquid crystal (PDLC) films were synthesized by the copolymerization of liquid crystalline polymer (LCP) precursor, urethane acrylate (UA), and mesogenic monomer (AI) at different conditions. The morphology of polymer matrix changed with the weight ratio of polymer/liquid crystal (LC) ratio and curing temperature, resulting in a large change in the droplet size of LC domains in the PDLC film. The components used in the synthesis of polymer matrix, that is, the weight ratio of LCP, AI, and UA, also strongly influenced the morphology of PDLC films. A small amount of LCP was copolymerized with UA and AI in the preparation of polymer matrix to improve the electrooptical properties such as the viewing angle. Added LCP also affected the morphology and the properties of PDLC. The hydrophobicity of LCP caused changes in the droplet size of LC domain in PDLC films and the anchoring energy between matrix polymer and LC droplets. As the hydrophobicity of the matrix increases, the droplet size of LC domain also increases; on the contrary, anchoring energy decreased, leading to the decrease of driving voltage.

Preparation of silver nanoparticles in hexagonal phase formed by nonionic Triton X-100 surfactant

Abstract Silver nanoparticles were prepared by reducing silver ions in the hexagonal phase formed by Triton X-100 in aqueous solution. Triton X-100 molecules have been used to form the hexagonal phase in aqueous solution as well as to reduce the silver ions into silver atoms. The hexagonal phase hindered the growth and aggregation of particles. The microstructure of the hexagonal phase was investigated by polarizing microscopy, 2 H NMR spectroscopy and small-angle X-ray diffraction. At the initial stage of the reaction, silver particles prepared in the hexagonal phase exhibited a size of 1–7 nm. As the reaction proceeded, particles grew up to about 30 nm as determined by transmission electron microscopy (TEM). The formation rate of silver particles was investigated by UV–Visible spectroscopy. It was found that the reaction temperature was an important factor for the rate of particle formation. With TEM, it was confirmed that surfactant aggregates, which have flexible structures, could not absolutely prevent particles from growing and aggregating. But, the results of polarizing microscopy, 2 H NMR spectroscopy and X-ray diffraction exhibited that the growth of particles could not cause a deformation of the original structure (hexagonal phase), which was employed as the reaction medium.

Compatibilizing effect of isocyanate functional group on polyethylene terephthalate/low density polyethylene blends

To evaluate the compatibilizing effects of isocyanate (NCO) functional group on the polyethylene terephthalate/low density polyethylene (PET/LDPE) blends, LDPE grafted with 2-hydroxyethyl methacrylate-isophorone diisocyanate (LDPE-g-HI) was prepared and blended with PET. The chemical reaction occurred during the melt blending in the PET/LDPE-g-HI blends was confirmed by the result of IR spectra. In the light of the blend morphology, the dispersions of the PET/LDPE-g-HI blends were very fine over the PET/LDPE blends. DSC thermograms indicated that PET micro- dispersions produced by the slow cooling of the PET/LDPE-g-HI blends were largely amorphous, with low crystallinity, due to the chemical bonding. The tensile strengths of the PET/LDPE-g-HI blends were higher than those of the PET/LDPE blends having a poor adhesion. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 447-453, 1998

Effective Formation of Silicone-in-Fluorocarbon-in-Water Double Emulsions: Studies on Droplet Morphology and Stability

ABSTRACT Silicone-in-fluorocarbon-in-water double emulsions were prepared by controlling carefully the characteristics of the emulsions composed of silicone, perfluoropoly-ethoxymethoxy difluorohydroxyethyl ether (PFPE–OH) and fluorosurfactant. In the emulsion formulation, PFPE–OH incorporated had a great influence on the droplet morphology and the stability of double emulsions. Moreover, it was observed that among the fluorocarbons, the silicone-in-fluorocarbon-in-water double emulsions could be formed effectively in the presence of a fluorosurfactant. The double emulsions prepared in this study maintained their initial emulsion stability for a long time at high temperature, meaning great usefulness in the cosmetic industry.

Improved compatibility of high‐density polyethylene/poly(ethylene terephthalate) blend by the use of blocked isocyanate group

The blocked isocyanate group (BHI) was synthesized to improve the storage stability of HI (2-hydroxyethyl methacrylate combined with isophorone diisocyanate) and characterized by Fourier transform infrared spectroscopy (FTIR). High-density polyethylene grafted with the blocked isocyanate group (HDPE-g-BHI) was used as a reactive compatibilizer for an immiscible high-density polyethylene/poly(ethylene terephthalate) (HDPE/PET) blend. A possible reactive compatibilization mechanism is that regenerated isocyanate groups of HDPE functionalized by BHI react with the hydroxyl and carboxyl groups of PET during melt blending. The HDPE-g-BHI/PET blend showed the smaller size of a dispersed phase compared to the HDPE/PET blend, indicating improved compatibility between HDPE and PET. This increased compatibility was due to the formation of an in situ graft copolymer, which was confirmed by dynamic mechanical analysis. Differential scanning calorimetry (DSC) analysis represented that there were few changes in the crystallinity for the continuous PET phase of the HDPE-g-BHI/PET blends, compared with those of the HDPE/PET blends at the same composition. Tensile strengths and elongations at the break of the HDPE-g-BHI/PET blends were greater than those of the HDPE/PET blends.

Monodisperse conducting colloidal dipoles with symmetric dimer structure for enhancing electrorheology properties

This study introduces an electrorheological (ER) approach that allows us to obtain remarkably enhanced ER properties by using monodisperse colloidal dimer particles. Two sets of colloidal particles, which are spheres and symmetric dimers, were synthesized employing the seeded polymerization technique. The aspect ratio of dimer particles was ~1.43. Then, the surface of the particles was coated with polyaniline by using the chemically oxidative polymerization method. After preparation of the particle suspensions having the same particle volume and concentration, their ER behavior was investigated with changing the electric field strength. At the same experimental condition, both shear stress and shear yield stress of the dimer particle suspension remarkably increased, compared with those of the spherical particle suspension. This attributes to the fact that the shape anisotropy of suspending particles effectively led to increase in the dipole moment under the electric field, thus resulting in formation of a well-structured colloidal chains between the electrodes.

Blends of polybutyleneterephthalate with ethylene-propylene elastomer containing isocyanate functional group

Abstract Ethylene–propylene elastomer (EPM) grafted with an isocyanate-containing monomer (HI) was blended with polybutyleneterephthalate (PBT), and its morphological, rheological, and mechanical properties were studied. The monomer HI was prepared by the reaction of 2-hydroxylethylmethacrylate and isophorone diisocyanate. The HI was successfully incorporated onto EPM backbone through solution graft reaction with radical initiator. When the PBT was blended with HI-grafted EPM (EHI), the morphologies of the dispersed phase displayed differences with respect to particle size and interfacial adhesion, when compared with those of the PBT/EPM blend. The increase in complex viscosity, storage modulus and impact strength of PBT/EHI blends ensured that the compatibility between PBT and EPM was improved through functionalization of EPM with the isocyanate moiety. These results are mainly due to in situ graft PBT–EPM copolymer that formed through the chemical reaction between the isocyanate group of EHI and hydroxyl or carboxyl end groups of PBT.

Electrical Properties of Composite Films Using Carbon Nanotube/Polyelectrolyte Self-Assembled Particles

ConclusionsfMCNT/polyelectrolyte coated PS particles were synthesized by LbL self-assembly to enhance dispersity of CNTs in CNT/PS composite films. The amount of fMCNTs on particles was efficiently controlled by adjusting the number of PDDA/fMCNT multilayers. The electrical properties of fMCNT/PS composite layer on the PMMA using fMCNT/ polyelectrolyte self-assembled particles were investigated. The fMCNT/PS composite layer on the PMMA showed the high electric conductivity because fMCNTs were well dispersed in composite films. Also, EMI SE over frequency rage of 50 MHz - 1.5 GHz was weakly measured around 1-5 dB depending on the different number of PDDA/fMCNT multilayers. Though the EMI SE of composite films was observed, the EMI SE was too low to be applied for practical applications. The electrical conductivity of fMCNT/PS composite layer on PMMA continuously increased with the stepwise growth of PDDA/fMCNT multilayers. It was suggested that electrical properties of composite films were efficiently controlled by using fMCNT/polyelectrolyte selfassembled particles.