Browsing by Author "Wu, KC"

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Melt processing of polypropylene/clay nanocomposites modified with maleated polypropylene compatibilizers
(2004)
Wang, Y
;
Chen, FB
;
Li, YC
;
Wu, KC
;
應用化學系
Maleic arthydride-grafted polypropylene (PPgMA) and organically modified clay composites were prepared in a plasticorder. PPgMAs, including PB3150, PB3200, PB3000, and E43, with a wide range of MA content and molecular weight were used. The structure was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM). PPgMA compatibilizers gave rise to similar degree of dispersion beyond the weight ratio of 3 to 1 with the exception of E43, which had the highest MA content and the lowest molecular weight. It was found that thermal instability and high melt index were responsible for ineffective modification by E43. Furthermore, PPgMA with low melting point and high melt index was compounded at low equilibrium temperature in order to maintain a certain level of torque. We then modified polypropylene/organoclay nanocomposites with different levels of PPgMA compatibilizers on a twin-screw extruder. The PP/E43/clay system, as shown through XRD patterns and TEM observation, yielded the poorest clay dispersion among the compatibilizers under investigation. The relative complex viscosity curves also revealed a systematic trend with the extent of exfoliation and showed promise for quantifying the hybrid structure of the nanocomposites. Mechanical properties and thermal stability were determined by dynamical mechanical analysis and thermogravimetric analysis, respectively. Though PPgMA with lower molecular weight and higher MA content could lead to good clay dispersion in PP/clay composites, it caused the deterioration in both mechanical and thermal properties of PP/PPgMA/clay composites. (C) 2003 Elsevier Ltd. All fights reserved.
Potassium ion recognition by 15-crown-5 functionalized CdSe/ZnS quantum dots in H2O
(2006-01-21)
Chen, CY
;
Cheng, CT
;
Lai, CW
;
Wu, PW
;
Wu, KC
Based on 15-crown-5 functionalized CdSe/ZnS quantum dots (QDs), we report a novel fluorogenic sensor to probe K+ ions in H2O; recognition of K+ can be achieved via the Forster type of energy transfer between two different color QDs, so that [K+] of the order of 10(-6) M can be promptly detected.
Spectroscopy and femtosecond dynamics of type-II CdTe/CdSe core-shell quantum dots
(2006-01-16)
Chou, PT
;
Chen, CY
;
Cheng, CT
;
Pu, SC
;
Wu, KC
Syntheses of CdTe/CdSe type-II quantum dots (QDs) using CdO and CdCl2, as precursors for core and shell, respectively, are reported. Characterization was made via near-IR interbond emission, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). Femtosecond fluorescence upconversion measurements on the relaxation dynamics of the CdTe core (in CdTe/CdSe) emission and CdTe/CdSe inter-band emission reveal that as the size of the core increases from 5.3, 6.1 to 6.9 nm, the rate of photoinduced electron separation decreases from 1.96, 1.44 to 1.07 X 10(12) s(-1). The finite rates of the initial charge separation ore tentatively rationalized by the small electron-phonon coupling, causing weak coupling between the initial and charge-separated states.