Browsing by Author "Li, AK"

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Effect of zirconia content on the oxidation behavior of silicon carbide/zirconia/mullite composites
(1998-09-01)
Tsai, CY
;
Lin, CC
;
Zangvil, A
;
Li, AK
;
材料科學與工程學系
The oxidation of hot-pressed SiC-particle (SiCp)/zirconia (ZrO2)/mullite composites with various ZrO2 contents, exposed in air isothermally at 1000 degrees and 1200 degrees C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO2 content on the oxidation behavior. A clear critical volume fraction of ZrO2 existed for exposures at either 1000 degrees or 1200 degrees C: the oxidation rate increased dramatically at ZrO2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO2 content could be explained by the percolation theory, when applied to the oxygen diffusivity in a randomly distributed two-phase medium. Morphologically, the composites with ZrO2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO2 contents less than the critical value revealed a much-thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO4) at 1200 degrees C, through the reaction between ZrO2 and the oxide product, could reduce the oxidation rate of the composite.
Fluorescent conjugated polymer films as TNT chemosensors
(2004-08-13)
Chang, CP
;
Chao, CY
;
Huang, JH
;
Li, AK
;
Hsu, CS
Three prototypical light emitting conjugated polymers, two poly(p-phenylene vinylenes) (MEH-PPV and DP10-PPV) and a poly(diphenylacetylene), were examined for chemosensor applications to detect explosive compounds such as 2,4,6-trinitrotoluene (TNT) and 2,4- and 2,6-dinitrotoluene (DNTs). All polymer thin films showed high fluorescence quenching sensitivity towards TNT and DNTs, indicating that a wide range of emissive conjugated polymers are potentially useful chemosensor materials for detecting landmines. The relative sensitivity of fluorescence quenching of the polymers by the analytes has been rationalized in terms of the vapor pressure of the analytes, the solubility parameters of the polymers and the analytes, and the relative energy levels of the polymers. (C) 2004 Elsevier B.V. All rights reserved.
New soluble poly(2,3-diphenylphenylene vinylene) derivatives for light-emitting diodes
(2005-04-22)
Yang, SH
;
Chen, JT
;
Li, AK
;
Huang, CH
;
Chen, KB
Soluble poly(2,3-diphenylphenylene vinylene) (DP-PPV) derivatives, poly(2,3-diphenyl-5-(4-heptyloxy-4'-oxytrimethylenediphenyl)phenylene vinylene) (P1), poly(2,3-diphenyl-5-[4-(4-pentylcyclohexyl)phenoxyl-propyl-p-phenylene vinylene) (P2) and poly(2,3-diphenyl-5-(2-(1, 4, 5-triphenyl-1H-2-imidazoloyl)-1-oxytrimethylene phenyl) phenylene vinylene) (P3), were synthesized. P1 and P2 contain liquid crystal side groups; while P3 contains a charge transport group. The polymers showed solid state UV-Visible absorption and photoluminescence in the range of 370-380 and 480-510 nm, corresponding to blue green emission. Similar to many other reported systems, the solution fluorescence spectra of P1 and P2 showed slight solvent dependency and blue-shifted with respect to those of the films. These were not the case for P3 which showed little solvent dependency and little blue shift in solution. Two-layer light-emitting devices with a simple ITO/PEDOT/polymer/Ca (Al) configuration were fabricated and characterized. (c) 2004 Elsevier B.V. All rights reserved.
Polarized blue emission based on a side chain liquid crystalline polyacrylate containing bis-tolane side groups
(2002-03-01)
Chang, SW
;
Li, AK
;
Liao, CW
;
Hsu, CS
;
應用化學系
A novel side chain liquid crystalline (LC) polyacrylate (1P) containing highly conjugated bis-tolane side groups was synthesized and used for polymer light emitting diodes application. Polymer 1P shows a nematic phase at room temperature. It exhibits a UV absorption peak at 330 run and emits a blue light at 425 inn. Polyimide (PI), polyaniline (PA) and poly(3,4-diethylenedioxythiophene) (PEDOT) were used as alignment materials for polymer 1P. The photoluminescence dichroic ratios of 1P on rubbed PI, PA and PEDOT films are 10.4, 8.3 and 7.3, respectively. The electroluminescence dichroic ratio of IP aligned on a PEDOT film is 6.1.
Poly(2,3-diphenylphenylene vinylene) derivatives having liquid crystalline side groups
(2000-09-01)
Li, AK
;
Yang, SS
;
Jean, WY
;
Hsu, CS
;
Hsieh, BR
Poly(2,3-diphenylphenylene vinylene) (DP-PPV) derivatives with pendant mesogene groups were synthesized. A biphenyoxyl or cyclohexylphenoxy moiety serves as the rigid mesogen core, a methylene chain as the spacer, and a alkyl or alkoxy group as the flexible terminal group. The optical properties of the polymers were investigated by UV-vis and photoluminescent spectroscopies. The polymer films emitted green-blue photoluminescence and electroluminescence. The phase transition behaviors of the polymers were characterized by a polarized optical microscope and a differential scanning calorimeter. The monomers did not show mesophases, while the polymers exhibited a nematic phase around 170-190 degrees C. The aligned films exhibited dichroism in absorption and emission spectra, implying that the polymers have potential for linearly polarized LED application.
Synthesis and characterization of poly(pyrrolyl methine)
(2001-09-01)
Yan, W
;
Li, AK
;
Hsu, CS
;
Zhang, ZC
;
Wan, MX
A novel small band-gap conjugated polymer - poly [(3-acetylpyrrole-2,5-diyl)(4-dimethylaminobenzyliene)(3-acetylpyrrolequinodimethane-2,5-diyl)] (PAPDMABE) - and its precursor were synthesized by a simple method and characterized by H-1-NMR, FT-IR, TGA and UV-VIS. The polymer can be dissolved in strong polar solvents such as DMSO, DMF or NMP. The band-gap energy of PAPDMABE, was found to be 0.95 eV. The conductivity of doped products with iodine falls in the range of a semiconductor.
Synthesis of substituted poly (arylene vinylene) films by vapor deposition polymerization
(2000-09-01)
Li, AK
;
Janarthanan, N
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
An efficient method for the synthesis of PPV based polymers, poly (2,5-dimethyl-1,4-phenylene vinylene) (DMe-PPV) and poly (2,5-dimethoxy-1,4-phenylene vinylene) (DOMe-PPV) were developed using 2,5-dimethyl-1,4-bis (chloromethyl) benzene and 2,5-dimethoxy 1,4-bis (chloromethyl) benzene via vapor phase pyrolysis and followed by vapor deposition polymerization. The structure of polymer films were confirmed by FT-IR, solid state NMR and elemental analysis. Thermal gravimetry analysis reveals that the precursor polymer films form a conjugated polymer after thermal conversion at 250 degrees C. The optical and electrical properties of the polymer films were investigated by UV-Vis absorption and photoluminescence spectroscopies. Electroluminescent devices were fabricated using these polymers.