Gyo Jic Shin

Recyclable and stable silver deposited magnetic nanoparticles with poly (vinyl pyrrolidone)-catechol coated iron oxide for antimicrobial activity.

This paper introduces a facile method to make highly stable and recyclable antimicrobial magnetic nanoparticles (NPs). Initially, magnetic iron oxide nanoparticles (IONPs) were coated with poly (vinyl pyrrolidone) conjugated catechol (PVP-CCDP). Afterward, silver nanoparticles (Ag(0)) were deposited onto PVP-CCDP coated IONPs using remain catechol. The prepared nanoparticles showed long term (~4 weeks) colloidal stability and redispersibility, respectively, against external magnetic field and over a broad range of pH (4-12). The NPs were characterized by UV-vis, SEM, XPS, and XRD measurements. TEM and DLS analyses showed that the mean particle size of PVP-CCDP coated IONPs/Ag(0) were about 72 nm. The recyclable magnetic NPs possessed a high antibacterial effect against the model microbes Staphylococcus aureus and Escherichia coli and could be separated easily using magnet following antibacterial test for repeated uses and maintained 100% antibacterial efficiency during three cycles. In MTT assay, the magnetic nanoparticles possessed no measureable cytotoxicity to live cells.

Influence of chemical structure on the optical properties of new side-chain polymers containing cholesterol

Poly[1-(cholesteryloxyhexyloxy)ethylene] (PHET) and poly[1-(cholesteryloxycarbonyl-hexyloxy)ethylene] (PHES) were prepared by reacting poly(vinyl alcohol) with cholesteryloxyhexyloxy bromides (CHB) or cholesteryloxycarbonylhexyloxy bromides (CEHB), and their thermal and optical properties were investigated. PHET and PHES exhibited monotropic cholesteric phases; however, their thermal behaviours depended on the cholesteryl groups and alkylene spacers with different chemical structures. PHET did not display reflection colours over its entire cholesteric range, whereas PHES did display reflection colours. These results suggested that the thermal stability and helical twisting power (HTP) of these polymers strongly depend on the difference in the chemical structures of the flexible spacer via cholesterol. The mesophase properties of PHET and PHES differed substantially from those of poly(cholesteryl-ω-acryloyloxyalkanoates). The results indicate that the mode of chemical linkage between the side-chain group and the main chain as well as that between the alkylene spacer and side chain play important roles in determining the thermal stability, mesophorphic structure and HTP of the cholesteric mesophases.

Photo alignment Behaviors of Photopolymer with Cinnamate Group by LPUV Method

The side chain photopolymer containing terminally substituted methoxy cinnamoyl ester was synthesized and characterized. The para position in the methoxy cinnamoyl group was connected with polymer backbone through 4 numbers of methylene spacer. A good thermal stability of photopolymer was measured by thermogravimatric analysis (TGA) measurement until 400 ℃ while the glass transition temperature was observed that high PMC according to the results of differential scanning calorimetry (DSC). The nematic liquid crystal (NLC) pretilt angle generated was about 0.06-1.66 by polarized different UV exposure energy. Especially, the low pretilt angle of the NLC was measured by the longer polarized UV exposure time. This result indicated that the NLC pretilt angle generated sensitively depends on the UV exposure time on the photopolymer layer.

Properties of Thermal Conductivity on Polyimide/Clay Nanocomposite Foams

We synthesized polyimide (based on ODA-PMDA) and polyimide foam and polyimide/clay foam that pore size was uniform about 1㎛. We identified that the clay layers are well dispersed in polyimide matrix and achieved exfoliation structure by X-ray diffraction. And we compared thermal conductivity of PI, PI foam, PI/clay foam. Thermal conductivity decreased up to maximum 28 % by introducing both pores and clay layers. Exfoliated structure of clay leads to decrease of thermal conductivity by thermal barrier effect. Also, the presence of clay could considerably reinforce the poor mechanical properties of polyimide by foam because of interfacial interaction between clay layers and polymer matrix. Through the this results, it has shown that this study may provide an effective method to prepare polymer/clay nanocomposite foams having exfoliation structure, and can be used as insulating material having low thermal conductivity.

Near Infrared Cut-Off Characteristics of Various Perovskite-Based Composite Films

Homogenous cesium tungsten tri-oxide (CsxWO3) and molybdenum tri-oxide (Cs0.33MoO3) powder was prepared by solvothermal reaction using (NH4)10H2(W2O7)6, H8MoN2O4 and Cs2CO3 aqueous solution followed by annealing. The cesium doped tungsten tri-oxide (CsxWO3) and the cesium doped molybdenum tri-oxide (CsxMoO3) nanocomposite films was deposited by the sol-gel bar-coating method onto PET-film (polyethylene terephthalate film, thickness 186 ㎛) substrate. The structure and sizes of ceramic particles was observed XRD and PSA spectrometer, the optical properties of their films were investigated by UV-VIS, NIR spectrometer. Synthesized particles typically formed cubic structure for good absorption of NIR, size observed as being 30-100 nm and 3 nanoparticles showed a high transmittance in the visible wavelength region as well as excellent shielding capability of near-infrared (NIR) wavelength, indicating that CsxWO3, Cs0.33MoO3 nanoparticles have a appropriate characteristic as solar filter applications.