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排序方式: 共有600条查询结果,搜索用时 15 毫秒
41.
Jaroslav Stejskal Pavel Kratochvíl Josef Urban G. S. Kapur Y. Lakshminarayana 《Polymer International》1993,30(1):81-87
Methyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, MwD ~ 108-109 g mol?1) and hydrodynamic radius (RhD ~ 50-120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size. Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles. 相似文献
42.
Jaroslav Hamerský 《Thin solid films》1976,38(1):101-107
CdSe films prepared in vacuum by sublimation from the compound at oxygen partial pressures in the residual atmosphere from 2.8 × 10?5 to 3.2 × 10?4 Torr and at substrate temperatures of 295 and 523 K were subjected to X-ray structural analysis. The results obtained are analysed and discussed in terms of some structures different from those of CdSe, e.g. CdSeO3 and CdSeO3.SeO2. 相似文献
43.
Jaroslav Kahovec 《Polymer Bulletin》1981,4(12):731-733
Summary Two methods of the introduction of aldehyde group into polystyrene skeleton are described. 相似文献
44.
Two criticality dosimetry systems were tested by Czech participants during the intercomparison held in Valduc, France, June 2002. The first consisted of the thermoluminescent detectors (TLDs) (Al-P glasses) and Si-diodes as passive neutron dosemeters. Second, it was studied to what extent the individual dosemeters used in the Czech routine personal dosimetry service can give a reliable estimation of criticality accident exposure. It was found that the first system furnishes quite reliable estimation of accidental doses. For routine individual dosimetry system, no important problems were encountered in the case of photon dosemeters (TLDs, film badge). For etched track detectors in contact with the 232Th or 235U-Al alloy, the track density saturation for the spark counting method limits the upper dose at approximately 1 Gy for neutrons with the energy >1 MeV. 相似文献
45.
Separation of platinum-metal-based homogeneous catalysts was achieved by their conversion to complexes of functionalized phosphines of the general formulae R3-n
P[(CH2)
x
CO2H)]
n
, R = Me, Et, Ph,n = 1, 2, 3,x = 1, 2, and [(HO2CCH2)PCH2]2, followed by extraction of the complexes into aqueous phase. This approach to regeneration of platinum metals from reaction mixtures after carrying out homogeneously catalyzed reactions was demonstrated on 11 examples of various types of reactions with Ru, Rh, Pd, Os, Ir and Pt compounds as catalysts. 相似文献
46.
We consider the problem of monitoring the Euclidean plane using rotating sensors with detection sectors and beam sensors. We assume that intruders can appear anywhere at any time and move arbitrarily fast, and may have full knowledge of the sensor network. We require that such intruders be detected within a finite amount of time. We give an optimal network for this problem consisting of a combination of rotating sensors of angle 0 and beam sensors that uses the minimum number of both types of sensors. We show a trade-off between the density of beam sensors needed and the angle of the detection sector of the rotating sensors. Secondly, we give a family of sensor networks using only rotating sensors for the same problem, that demonstrate a trade-off between the detection time and the density of rotating sensors used. We show that the density of rotating sensors required in this case can be significantly reduced by increasing the angle of detection sectors. Finally, we show that our results on the infinite plane can be used to derive sensor networks that monitor some finite regions using a density of sensors that is asymptotically the same, or close to that of the infinite plane case. 相似文献
47.
Libor Dostl Ale Ri
ka Jaroslav Hole
ek Roman Jambor 《Inorganic chemistry communications》2010,13(12):1470-1472
The synthesis of double O,C,O-chelated diorganotin(IV) compound L2SnBr2 (1), where L is 2,6-(MeOCH2)2C6H3?, the precursor for the synthesis of Sn ← O intramolecularly coordinated organotin(IV) cations is reported. Treatment of compound 1 with SnBr4 yielded the double O,C,O-chelated diorganotin(IV) ionic pair [L2SnBr]+ [SnBr5·THF]? (2). Both compounds 1 and 2 were characterized by 1H, 13C, 119Sn NMR and molecular structure of compound 2 was established by X-ray diffraction. 相似文献
48.
Jaroslav Stejskal Miroslava Trchová Jir̆ina Hromádková Jana Kovár̆ová Andrea Kalendová 《Polymer International》2010,59(7):875-878
The carbonization of nanostructures afforded by conducting polymers represents a new route to the preparation of functional nanostructured carbons. The exposure of colloidal polyaniline particles stabilized with poly(N‐vinylpyrrolidone) or silica nanoparticles at 650 °C in inert atmosphere led, in both cases, to nitrogen‐containing carbonaceous materials with specific surface areas of 200 and 205 m2 g?1, respectively, and conductivities of 8.3 × 10?7 and 1.9 × 10?10 S cm?1, respectively. The latter material contained 77 wt% of silica. The original particulate nanostructure of the samples was preserved after carbonization. The carbon‐to‐nitrogen atomic ratio was 7.2 and 7.9; the nitrogen content in the carbonized polyaniline–poly(N‐vinylpyrrolidone) particles was 10.8 wt%. Thermogravimetric analysis in air revealed their stability to be up to 500 °C. This is comparable with commercial multi‐wall carbon nanotubes, which have similar areas of application. The nitrogen‐containing carbons are potentially useful as supports for catalysts and in applications where carbon of higher hydrophilicity would be of benefit. Copyright © 2010 Society of Chemical Industry 相似文献
49.
It was demonstrated that non-homopolymerizing derivatives of 6-caprolactam: 7-cyclohexyl-1-aza-2-cycloheptanone (I) and 7-isopropyl-5-methyl-1-aza-2-cycloheptanone (II) were polymerizing with 6-caprolactam under conditions of the socalled hydrolytic polymerization. With its increasing content in the initial reaction mixture the copolymerization rate, the equilibrium content of the copolymer, and the reduced viscosity decreased. Lactam (I) was a more reactive comonomer in comparison with lactam (II). 相似文献
50.
M. K. Mohanapriya Kalim Deshmukh Jaroslav Kadlec Kishor Kumar Sadasivuni Muhammad Faisal N. A. Nambi Raj 《Polymer-Plastics Technology and Engineering》2020,59(8):847-863
ABSTRACTNovel tertiary nanocomposite films comprising of poly (vinyl alcohol) (PVA), poly (4-styrenesulfonic acid) (PSSA) and titanium dioxide (TiO2) nanoparticles (NPS) were prepared using simple solvent casting method. The structural, thermal, morphological, thermo-mechanical and electromagnetic interference (EMI) shielding properties of PVA/PSSA/TiO2 nanocomposite films were investigated. The EMI shielding effectiveness (SE) of PVA/PSSA/TiO2 nanocomposite films in the X and Ku band was found to be 12 dB and 13 dB respectively at 25 wt% TiO2 NPs loading. These results demonstrate the possible applications of PVA/PSSA/TiO2 nanocomposite films as low cost, lightweight and flexible material for EMI shielding. 相似文献