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841.
842.
843.
We report on the bulk and surface properties of dispersions consisting of nonstoichiometric polyelectrolyte complex (PEC) nanoparticles. PEC nanoparticles were prepared by mixing poly(l-lysine) (PLL) or poly(diallyldimethylammonium chloride) (PDADMAC) with poly(maleic acid-co-alpha-methylstyrene) (PMA-MS) or poly(maleic acid-co-propylene) (PMA-P). The monomolar mixing ratio was n-/n+ = 0.6, and the concentration ranged from 1 to 6 mmol/L. Subsequent centrifugation enabled the separation of the excess polycation, resulting in a stable coacervate phase further used in the experiments. The bulk phase parameters turbidity and hydrodynamic radius (R(h)) of the PEC nanoparticles showed a linear dependence on the total polymer content independently of the mixed polyelectrolytes. This can be interpreted by the increased collision probability of the polyelectrolyte chains when the overlap concentration is approached or exceeded. Different morphologies of the cationic PEC nanoparticles, which were solution-cast onto Si supports, were obtained by atomic force microscopy (AFM). The combinations of PLL/PMA-MS and PDADMAC/PMA-MS revealed more or less hemispherical particle shapes, whereas that of PLL/PMA-P revealed an elongated needlelike particle shape. Circular dichroism and attenuated total reflection Fourier transform infrared (ATR-FTIR) measurements proved the alpha-helical conformation for the PEC PLL/PMA-P and the random coil conformation for the PEC PLL/PMA-MS. We conclude that stiff alpha-helical PLL induces anisotropic elongated PEC nanoparticles, whereas randomly coiled PLL forms isotropic spherical PEC nanoparticles. 相似文献
844.
The variational calculation of Siegert eigenvalues has previously been shown to provide reliable positions and widths for atomic resonances. This approach is herein extended to molecular problems, and the first such calculations for a molecular autoionizing system, He(21,3S)+H→ He+H++e?, are reported. 相似文献
845.
Ohne Zusammenfassung 相似文献
846.
D. Hreniak W. Strek A. Opalińska M. Nyk M. Wołcyrz W. Lojkowski J. Misiewicz 《Journal of Sol-Gel Science and Technology》2004,32(1-3):195-200
A sol–gel method for the synthesis of nanosized powders of yttrium disilicate doped with Tb3 + is presented. The influence of grain size and annealing temperature on the structure and luminescence properties of the materials obtained has been investigated. The preparation of glass-ceramic composite has been also described. The effect of incorporating the nanocrystals into sol–gel silica glasses on their physicochemical properties has been shown and discussed. A lack of influence of the annealing above 1300°C on the lifetimes measured for the nanocrystals embedded in the glass, as compared to the Y2Si2O7:Tb3 + powders, has been observed. 相似文献
847.
A. S. Paschoa M. Cholewa K. W. Jones N. P. Singh M. E. Wrenn 《Journal of Radioanalytical and Nuclear Chemistry》1987,115(2):231-240
A combination of two techniques, PIXE (particle induced x-ray emission) and RBS (Rutherford backscattering), is proposed as an analytical tool to measure uranium and thorium in environmental and biological samples and in the study of the micro-distribution of uranium is low Z matrices such as biological tissue.Work supported by U.S. Department of Energy Contracts DE-AC02-76CH-00116 (MC, KWJ) and DE-AC02-76EV-00119 (NPS, MEW). One of us (ASP) is grateful to FINEP (Financiadora de Estudos e Projetos) and CNPq (Conselho Nacional de Desenvolvimento Cientifico e Technológico). 相似文献
848.
Norton P. Peet Shyam Sunder Robert J. Barbuch Edward W. Huber Ester M. Bargar 《Journal of heterocyclic chemistry》1987,24(6):1531-1535
Treatment of o-nitrobenzenesulfonyl chloride ( 3 ) with 5-aminotetrazole (5-AT) gave [(2-nitrophenyl)-sulfonyl]carbamimidic azide ( 6 ), a ring-opened isomer of the expected N-(1H-tetrazol-5-yl)-2-nitrobenzenesulfonamide ( 4 ). Sulfonylcarbamimidic azide 6 was converted to 2-amino-N-(aminoiminomethyl)benzene-sulfonamide ( 7 ) with ethanolic stannous chloride, and to 3-amino-1,2,4-thiadiazine 1,1-dioxide ( 8 ) with sodium dithionite. Methanesulfonyl chloride ( 9 ) and 5-AT gave 2-(methylsulfonyl)carbamimidic azide ( 10 ), which isomerized to 5-[(methylsulfonyl)amino]-1H-tetrazole ( 11 ) in warm ethanol. Attempted cycloaddition of 2-(phenylsulfonyl)carbamimidic azide ( 13 ) and ethyl vinyl ether led only to alkylated tetrazole products. In addition, other tetrazole-alkylating reactions are described. Isomers produced from these alkylations were differentiated with 13C nmr spectroscopy. 相似文献
849.
O. L. Shaffer V. L. Dimonie M. S. El-Aasser J. W. Vanderhoff 《Journal of polymer science. Part A, Polymer chemistry》1987,25(9):2595-2603
A series of poly(styrene)/poly(styrene-co-acrylonitrile) core-shell latexes were synthesized by seeded emulsion polymerization. The dried latex was dissolved in toluene and then cast on the surface of water to form a very thin film (60–90 nm). Phase separation in the thin film was studied by transmission electron microscopy (TEM). Electron micrographs of these thin films yielded fine structure and interesting morphology that was unattainable by ultramicrotoming of the corresponding compression-molded specimens. Glass transition temperatures and percent grafted polystyrene were correlated with the TEM results. As grafting increases, mixing of the two phases improves, with the resulting Tg value being between the two Tg's of poly(styrene) and poly(styrene-co-acrylonitrile). 相似文献
850.