Browsing by Author "Mo, Te-Cheng"

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Synthesis and characterization of polyimide-silica nanocomposites using novel fluorine-modified silica nanoparticles
(2007-04-15)
Mo, Te-Cheng
;
Wang, Hong-Wen
;
Chen, San-Yan
;
Dong, Rui-Xuan
;
Kuo, Chien-Hung
Polyimide-silica nanocomposites were synthesized with 4,4'-oxydianiline, 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine-modified silica nanoparticles. Fluorinated precursors such as 4",4'"-(hexafluoroisopropylidene)bis(4-phenoxyaniline) (6FBPA) and 4,4'-(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polymide-silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide-silica nanocomposites containing 6FBPA-modified silica exhibited more uniformity than those of the nanocomposites containing BISAF-modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA-modified silica but not BISAF-modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA-modified silica nanoparticles demonstrated an effective way of synthesizing low-dielectric-constant polyimide-silica nanocomposites. (c) 2007 Wiley Periodicals, Inc.
Synthesis and characterization of polyimide/multi-walled carbon nanotube nanocomposites
(2008-04-01)
Mo, Te-Cheng
;
Wang, Hong-Wen
;
Chen, San-Yan
;
Yeh, Yun-Chieh
;
材料科學與工程學系
Polyimide/multi-walled carbon nanotube (PI-MWNT) nanocomposites were fabricated by an in situ polymerization process. Chemical compatibility between the PI matrix and MWNTs is achieved by pretreatment of the carbon nanotubes in a mixture of sulfuric acid and nitric acid. The dispersion of MWNTs in the PI matrix was found to be enhanced significantly after acid modification. The glass transition (T-g) and decomposition (T-d) temperature of PI-MWNT nanocomposites were improved as the MWNT content increased from 0.5 to 15 wt%. The storage modulus of the PI/MWNT nanocomposites is nine times higher than that of pristine PI at room temperature. The tensile strength of PI doubles when 7 wt% MWNTs is added. The dielectric constant of the PI-MWNT nanocomposites increased from 3.5 to 80 (1 kHz) as the MWNT content increased to 15 wt%. The present study demonstrates that enhanced mechanical properties can be obtained through a simple in-situ polymerization process.
Synthesis and dielectric properties of polyaniline/titanium dioxide nanocomposites
(2008-09-01)
Mo, Te-Cheng
;
Wang, Hong-Wen
;
Chen, San-Yan
;
Yeh, Yun-Chieh
;
材料科學與工程學系
Two series of polyaniline-TiO2 nanocomposite material,, were prepared in base form by in situ polymerization of aniline will inorganic fillers using TiO2 nanoparticles (P25) and TiO2 colloids (Hombikat), respectively. The effect of particle sizes and contents of TiO2 materials on their dielectric properties was evaluated. The as-synthesized polyaniline-TiO2 nanocomposite materials were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), thermal analysis (DTA/TGA), and X-ray diffraction (XRD). Dielectric properties of polyaniline-TiO2 nanocomposites in the form of films were measured at 1 KHz-1 MHz and a temperature range of 35-150 degrees C. Higher dielectric constants and dielectric losses of polyaniline-TiO2 nanocomposites than those of neat PANI were found. PANI-TiO2 nanocomposites derived from P25 exhibited higher dielectric constants and losses than those from Hombikat TiO2 colloids. Electrical conductivity measurements indicate that the conductivity of nanocomposites is increased with TiO2 content. The dielectric properties and conductivities are considered to be enhanced due to the addition of TiO2 which might induce the formation of a more efficient network for charge transport in the base polyaniline matrix. (c) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.