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Lee A.,Insilicotech Co. | Kim K.H.,Insilicotech Co. | Kim D.,Insilicotech Co. | Choi S.-H.,Insilicotech Co. | And 6 more authors.
Computational Materials Science | Year: 2010

As a core structure for a new functional dye which can be used as materials for electronic devices such as field-effect transistors or light-emitting diodes, indenofluorene and indenopyrazine have been studied. CIS/6-31G* level was applied to optimize the geometry of the first excited state used to calculate the emission spectrum. Their UV absorption and PL emission spectra were calculated by using time-dependent density functional theory (TDDFT) method at B3LYP/6-31G* level. The influence of THF solvent was considered using polarized continuum model TDDFT (PCM-TDDFT) method as well. PCM-TDDFT results are red-shifted by about 10 nm in comparison to the corresponding predicted absorption and emission maximum in vacuum. In PCM-TDDFT results, the absorption maxima of indenopyrazine were red-shifted by about 25 nm compared to those of indenofluorene. This spectral shift, induced by the nitrogen atoms in the pyrazine ring of indenopyrazine, are explained by the analysis of electronic structures of indenofluorene and indenopyrazine and the atomic contributions of the pyrazine nitrogen atoms to the frontier molecular orbital of indenopyrazine. © 2009 Elsevier B.V. All rights reserved. Source

Park H.-S.,Hanyang University | Cho B.-S.,Hanyang University | Yoo E.-S.,KITECH Textile Ecology Laboratory | Ahn J.-B.,NoRoo Bee Chemical Co | Noh S.-T.,Hanyang University
Applied Chemistry for Engineering | Year: 2011

We made suspension of fumed silica in polyethylene glycol (PEG), studied rheological behavior as functions of contents of silica, dispersion condition, PEG molecular weight, temperature and contents of humidity. Rheological behavior of suspension was determined critical shear rate and rise of viscosity using rheometer AR2000. Suspension were PEGs of molecular weight 200, 400, and 600. Fumed silica suspensions of which silica contents are 5, 7, 9, 13, and 18% were prepared by normal mixing, homogenization and bead milling process. We observed their rheological behaviors at 10, 20, 30, and 40 °C. As the PEG molecular weight and contents of silica increase, the critical shear rate was lowered. As the temperature increased, the critical shear rate was increased. Humidity contents of dispersion don't influence on the critical shear rate, but dispersion processes greatly affect the critical shear rate. The critical shear rate of suspensions prepared by the mixing process was the lowest, and that of suspensions prepared by the bead milling process was the highest. The rise in the shear viscosity of suspensions prepared by the mixing process is higher than that of suspensions prepared by the bead milling process. This was dependent on the dispersion condition of silica particle by dispersion process. Source

Hwang S.Y.,Advanced Technology R and nter 911 | Yoon W.J.,Hanyang University | Yun S.H.,Advanced Technology R and nter 911 | Yoo E.S.,KITECH Textile Ecology Laboratory | And 2 more authors.
Macromolecular Research | Year: 2013

The goal of this study was to prepare functionalized, ultrathin nanofibers using mesoporous materials (TS-1 zeolite) with maximum capability to both absorb drug and control drug release (these fibers are herein referred to as PZ-01); a second goal was to prepare nanofibers that exhibit biodegradability after drug release. Under optimal conditions, the characteristic of TS-1 zeolite enabled the preparation of ultrathin nanofibers with diameters below 100 nm, or one-twentieth the size of homo-poly(butylene succinate) (PBS) fibers. In addition, PZ-01 nanofibers exhibited high drug loading capacity compared to homo-PBS fibers. This result was attributable to the large surface area of ultrathin nanofibers and to the strong ionic interaction between hydrophilic drugs and the metal ions of TS-1 zeolite. In vitro cytostatic assay indicated that prepared PZ-01 has cytostatic action toward both Gram-positive and Gram-negative bacteria. The excellent drug wetting behavior of PZ-01 led to longer drug-release times. After drugrelease tests, antibacterial tests confirmed that homo-PBS fibers had diminished antibiotic activity regardless of the type of bacteria, whereas the antibacterial activity of tested PZ-01 was highly efficient against both Gram-positive and Gram-negative bacteria. In the cell viability test, PZ-01 exhibited a greater decrease in cytotoxicity and an increase in cell viability compared with the homo-PBS nanofiber. Based on this research, we anticipate that these materials will be promising candidates for biomedical applications such as biofilters for microbes, wound dressings, and drug-delivery products. © 2013 The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht. Source

Hwang S.Y.,Advanced Technology Randnter | Yoon W.J.,Hanyang University | Yoo E.S.,KITECH Textile Ecology Laboratory | Im S.S.,Hanyang University
Macromolecular Research | Year: 2012

In this study, we investigated the effects of mesoporous titanium silicate (TS-1) zeolite on the melting behavior and isothermal crystallization in poly(butylene succinate) (PBS)/TS-1 zeolite hybrid composites (PTHC). Isothermal crystallization results revealed that TS-1 zeolite acted as a nucleation agent in PTHC, thus the t1/2 of PTHC was faster than that of homo-PBS. However, the nucleation effect of TS-1zeolite did not depend on the TS-1 zeolite content. The large surface area of the mesoporous structure readily formed molecular chains inside and outside of the pore mouths of TS-1 zeolite, covering the nucleation site, as a result of the byproduct deposition during polymerization. At isothermal crystallization, temperatures ranging from 88 to 92 oC, nucleation of TS-1 zeolite occurred because of the presence of free byproducts and the formation of a molecular chain in the pore mouths. In contrast, isothermal temperatures ranging from 80 to 84 oC resulted in ineffective nucleus activation because of the steric hindrance in the porous structure. Synchrotron small-angle X-ray scattering (SAXS) analysis revealed that TS-1 zeolite can accelerate lamellar recrystallization during heating. Source

Park J.Y.,Hanyang University | Hwang S.Y.,Advanced Technology R and nter and 911 | Yoon W.J.,Hanyang University | Yoo E.S.,KITECH Textile Ecology Laboratory | Im S.S.,Hanyang University
Macromolecular Research | Year: 2012

Blends of poly(lactic acid) (PLA) and poly(ethylene terephthalate glycol) (PETG) of various compositions were prepared by melt compounding and their compatibilities, physical properties, and isothermal crystallization behaviors were investigated. The calculated solubility parameters of PETG are similar to those of PLA. The interaction parameter between PLA and PETG was derived from the Flory-Huggins theory and predicted that PLA and PETG are miscible when PETG contents are below 22 wt%. In accordance with this result, the tan δ peak and glass transition temperatures of blends determined from dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed a single peak at PETG contents lower than 22 wt%. Tensile test results showed that the elongation at the break of blends increased with an increase in PETG content. DSC and isothermal crystallization results showed that PETG accelerates the crystallization rate of PLA at PETG contents lower than 22 wt%, indicating that PETG acts as a nucleation agent in the crystallization of PLA. Wide angle X-ray diffraction results (WAXD) showed that the crystalline structure of PLA is not affected by the incorporation of PETG. © The Polymer Society of Korea 2012. Source

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