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41.
Thomas R. Gengenbach Zoran R. Vasic Sheng Li Ronald C. Chatelier Hans J. Griesser 《Plasmas and Polymers》1997,2(2):91-114
The properties and composition of plasma polymer surfaces stored in air can change considerably over time, especially as a
result of oxidative reactions. When plasma polymers contain an element other than O, it is possible to probe for mechanisms
in addition to oxidation that contribute to the aging of the surface. Plasma polymers containing N were fabricated from either
1,3-diaminopropane (DAP),n-heptylamine (nHA), or allylamine (AA), and studied by X-ray photo-electron spectroscopy (XPS) and air/water contact angles
(CA). For each of the plasma polymers, a multiexponential increase in the O/C ratio was observed over time using XPS. The
N/C ratios remained constant (AA) or decreased somewhat (nHA and DAP). In contrast, the trends in CA values differed, declining
for the nHA surfaces, rising for the AA, and changing little for the DAP. Surface roughness, assessed by scanning tunnelling
or atomic force microscopy, did not change over time. The diverse adjustments in the polarity of each surface and the similar
compositional changes between them are reconcilable if the aging of the plasma polymer surface is a manifestation of the superposition
of concurrent oxidative reactions and partial surface reorientation; the former introduce polar groups and the latter transports
then from the surface to deeper regions beyond the CA probe depth but within the XPS analysis depth. These processes vary
between different plasma polymers. Data for the alkylamine plasma polymers is also compared with that for two plasma polymers
fabricated from methanol. The change in composition, but not polarity, of the DAP surface after 4 days of storage demonstrates
the importance of using multiple techniques to characterize the aging of plasma polymer surfaces. 相似文献
42.
采用二硫化碳重结晶富勒烯混合物或二硫化碳二次抽提烟灰以提取高富勒烯(higherfulerenes,Cn,n>70)。产物经高效液相色谱分析,高富勒烯的含量从1%分别提高到4%和6%;经激光飞行时间质谱证明,产物中除含主要成分C60和C70以外,还含有C76、C78、C82、C84以及更高碳原子的富勒烯。 相似文献
43.
Jie Chen Rong Ji Dai Bin Tong Sheng Yuan Xiao Wei Wei Meng 《中国化学快报》2007,18(1):10-12
The reduction of 4-nitrophenol catalyzed by nitroreductase in the presence of NADH was investigated in this paper.4-Amino- phenol and 4-bydroxylamino-phenol were found in the reductive products.The relationship between reaction time and the reductive ratio were studied.The similar reducing ratios of 4-nitrophenol were obtained under aerobic and anaerobic conditions.The results indicated that an oxygen-insensitive reaction was proceeded in the reduction of 4-nitrophenol and nitroreductase was an oxygen- insensitive enzyme.The reductive products of 4-nitrophenol were determined by HPLC and MS. 相似文献
44.
45.
BODIPY dyes are privileged fluorophores that are now widely used in highly diverse research fields. An overview of BODIPY dyes and a summarization of the different synthetic methodologies reported for direct C-H functionalization of the BODIPY framework have been provided. 相似文献
46.
A series of leaching experiments with H2O, HCl, HNO2 and HF were carried out on a sample of pitchblende from Africa. Anomalously high231Pa/235U ratios, which were not accompanied by similar enhancements of234U/238U and235U/238U ratios, were observed in some uranium fractions. The observed231Pa/235U ratios varied between the values of 0.035±0.005 and 2,000±300 (Ci/Ci). These results are interpreted as due, primarily, to the difference in the chemical properties of protactinium and uranium, rather than to the alpha-recoil effects. 相似文献
47.
Xin Sheng Li Yao Jun Zhang Qin Xin Chun Xin Ji Yan Fen Miao Li Wang 《Reaction Kinetics and Catalysis Letters》1996,57(1):177-182
Volumetric H2-uptake measurements on an Mo2N (79 m2g–1) sample reduced at 673 K have been carried out and the uptake isotherms in the temperature range of 308–623 K have been determined. Both the total and reversible hydrogen uptake increased with the uptake temperature. The irreversible hydrogen uptake increased abruptly when the uptake temperature was raised up to 423 K. The maximum of irreversible hydrogen uptake was measured at 473 K. The HIR/Mo ratio calculated from the uptakes obtained in the temperature range of 308–623 K varies in the range of 0.0010–0.0202. One possible mechanism for hydrogen adsorption is proposed to be heterolytic dissociation on Mo-N paris, in which the molybdenum atoms are in unsaturated coordination. 相似文献
48.
X. Liu X. Sheng J. K. Lee M. R. Kessler 《Journal of Thermal Analysis and Calorimetry》2007,89(2):453-457
Conversion (α) and the glass transition temperature (T
g) were investigated during the isothermal cure of endo-dicyclopentadiene (DCPD) with a Grubbs catalyst for different temperatures using differential scanning calorimetry. Conversion
vs. In (time) data at an arbitrary reference temperature were superposed by horizontal shift and the shift factors were used
to calculate an Arrhenius activation energy. Glass transition temperature vs. conversion data fell on a single curve independent of cure temperature, implying that reaction of the norbornene and cyclopentene
ring of DCPD proceeds in a sequential fashion. Implications of the isothermal reaction kinetics for self-healing composites
are discussed. 相似文献
49.
The influence of cross-linking agents on ring-opening metathesis polymerized thermosets 总被引:1,自引:0,他引:1
The addition of suitable cross-linking agents with norbornene-based monomers has significant effects on the thermal properties
of the resulting polymers formed by olefin metathesis. Ethylidene norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD) were mixed separately with various loadings of three different cross-linking agents and then polymerized with the addition
of Grubbs’ catalyst. The polymerization kinetics and resulting glass transition temperature (T
g) of the systems were evaluated by differential scanning calorimetry (DSC).
The addition of the first cross-linking agent, norbornadiene (CL-1), to both endo-DCPD and ENB resulted in decreasing glass transition temperatures with increasing concentrations. In contrast, the addition
of the other two cross-linking agents (CL-2 and CL-3), which were both custom synthesized bifunctional norbornyl systems,
to both endo-DCPD and ENB resulted in a monotonic increases in T
g with cross-linker concentration. By tailoring the loading of these custom cross-linking agents, the properties of these polymer
systems can be controlled for various applications, including self-healing composites. 相似文献
50.
Yinghong Sheng Jerzy Leszczynski Thuc-Quyen Nguyen Anu Bamgbelu 《Structural chemistry》2007,18(6):827-832
A theoretical study using density functional theory was performed to understand the structure/property relationship of the
cationic conjugated polyelectrolytes, poly[9,9-bis-(6′-N,N,N-trimethylammonium) hexyl] fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT-X, where X = Br). The torsion angle between the fluorene and benzothiadiazole units in the PFBT monomer was found to substantially affect
the structural and electronic properties of the cationic PFBT monomer. The changes of geometrical parameter, HOMO and LUMO energy levels, and band gap, as well as the absorption maximum
are discussed in terms of the torsion in the PFBT monomer structure. For comparison, its neutral analogue, the monomer of
poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) was also studied. The length of conjugation backbone was also examined. 相似文献