Browsing by Author "Jeng, US"

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Binding effect of surface-modified cadmium sulfide on the microstructure of PS-b-PEO block copolymers
(2004-06-15)
Jeng, US
;
Sun, YS
;
Lee, HY
;
Hsu, CH
;
Liang, KS
CdS nanoparticles with surfaces modified by mercaptoethanol have been synthesized for greater solubility in dimethylformamide (DMF) and the ability to preferentially bind to the poly(ethylene oxide) (PEO) blocks of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer. The size of the surface-modified CdS nanoparticles (M-CdS) in DMF can be characterized by the Schultz distribution of a mean radius of 18.4 Angstrom and a polydispersity of 0.5, using small-angle X-ray scattering (SAXS). These M-CdS nanoparticles can further disperse in the PS-b-PEO, with a slightly larger mean radius than that observed in DMF. The uptake of M-CdS nanoparticles for the PEO blocks of the PS-b-PEO saturates around 7% in volume fraction. The binding of the nanoparticles promotes a segregation of the PEO/nanoparticles and leads to spherical PEO/M-CdS microdomains in the composite film with a greatly enhanced thermal stability. The structural information obtained from X-ray scattering agrees well with the transmission electron microscopy images and differential scanning calorimetry results.
CdS nanoparticles induce a morphological transformation of poly(styrene-b-4-vinylpyridine) from hexagonally packed cylinders to a lamellar structure
(2005-07-26)
Yeh, SW
;
Wei, KH
;
Sun, YS
;
Jeng, US
;
Liang, KS
Mercaptoacetic acid-modified CdS nanoparticles disperse selectively in the poly(4-vinylpyridine) domains of poly(styrene-b-4-vinylpyridine) (S4VP) block copolymer as a result of the formation of hydrogen bonds. This process in turn induces the morphological transformation of S4VP from a hexagonally packed cylinder structure into a lamellar structure, as evidenced from transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering studies. This transformation is consistent with that suggested by a theoretical prediction of the phase diagram of the mixed diblock copolymer/nanoparticle system.
Morphological transformation of PS-b-PEO diblock copolymer by selectively dispersed colloidal CdS quantum dots
(2003-10-21)
Yeh, SW
;
Wei, KH
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Sun, YS
;
Jeng, US
;
Liang, KS
Phase behavior in polystyrene-block-poly (ethylene oxide) nanocomposites with colloidal CDS quantum dots upon heating.
(2004-08-22)
Sun, YS
;
Jeng, US
;
Liang, KS
;
Yeh, SW
;
Wei, KH
Preparation and supramolecular self-assembly of a polypeptide-block-polypseudorotaxane
(2005-07-26)
Lee, HF
;
Sheu, HS
;
Jeng, US
;
Huang, CF
;
Chang, FC
We have successfully prepared a new class of self-assembled biomaterial: a polypeptide-block-polypseudorotaxane diblock copolymer. This diblock copolymer is comprised of an a-helical polypeptide rod, based on gamma-benzyl-L-glutamate, and an originally coiled segment P(EO19-r-PO3); it forms inclusion complexes with a-cyclodextrins (alpha-CDs) to give crystalline polypseudorotaxanes. Formation of the polypseudorotaxane converts the conformation of P(EO19-r-PO3) from a flexible chain into a rodlike structure, which results in a novel block copolymer exhibiting a rod-rod conformation. Intrinsic interactions (e.g., the polypseudorotaxane's channel-type crystallization, the polypeptide's secondary structure, and microphase separation) within and between these rod-rod diblock copolymers contribute to their hierarchical self-assembly behavior, which we characterized using DSC, H-1 NMR spectroscopy, C-13 CP/MAS NMR spectroscopy, WAXS, and SAXS. The data obtained from the WAXS and SAXS studies clearly indicate the formation of juxtaposed bilayer-like nanostructure featuring hexagonally packed PBLG stacks and channel-type polypseudorotaxane moieties.
Transitions of domain ordering and domain size in a spherical-forming polystyrene-block-poly(ethylene oxide) copolymer and its composites with colloidal cadmium sulfide quantum dots
(2006-02-08)
Sun, YS
;
Jeng, US
;
Liang, KS
;
Yeh, SW
;
Wei, KH
With specific annealing schemes applied to a neat polystyrene-block-poly(ethylene oxide) (SE) and its composites with cadmium sulfide quantum dots (CdS QD), we have observed microdomain structures and phase transitions in the system using temperature-resolved small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Both TEM images and SAXS results show clearly that incorporation of surfactant-tethered US QD preferentially into PEO blocks leads to increases in thermal stabilities of both bcc-packed lattice (referred as long-range order) and microdomains themselves in the sphere-forming SE/CdS composites. The bcc-packed lattice in the SE/CdS composites sustains better than that in the neat SE, during a temperature elevation to similar to 160 degrees C, at which the bcc-packed SE/CdS spheres start to transform into micelles with a short-range liquid-like order. Quantitative model analysis shows that the PEO/CdS micelles can retain their size in the SE/CdS composites up to 200 degrees C, whereas the PEO micelles shrink after the softening of the PS matrix around 100 degrees C and disassociate largely into the PS matrix of the neat SE at 160 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.