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401.
Ivica Vujčić Tamara Gavrilović Milica Sekulić Slobodan Mašić Bojana Milićević Miroslav D. Dramićanin 《辐射效应与固体损伤》2013,168(11-12):1054-1067
ABSTRACTYPO4 phosphors doped with trivalent ion Pr3+ were prepared by sol–gel method and treated with different doses of gamma radiation, from 0.25 MGy to 4 MGy. Effects of radiation on morphology, structure and luminescent properties were analyzed. Also, the influence of radiation on the change in the color of the samples was examined. The color efficiency of powders was evaluated by colorimetric analysis (CIE and L * a * b system). It has been observed that powders change color under the influence of radiation, i.e. they pass from white to pinkish red. Also, it has been determined that the radiation affects morphology change, as the particle size increases with increasing of the radiation dose. With the increase in the radiation dose, the emission intensity of samples decreases. The structure remains almost unchanged after irradiation, and the intensity constantly decreases with increasing of dose. 相似文献
402.
Tatjana Friedrich Tamara Mielke Monika Domogalla Maria Hentschel Katharina Kraus Bernd Tieke 《Macromolecular rapid communications》2013,34(5):393-398
Photoreactive and thermoresponsive N‐isopropylacrylamide (NIPAM)–surfmer copolymer hydrogels containing 4,4′‐di(6‐sulfato‐hexyloxy)azobenzene (DSHA) dianions are described. The functional hydrogels are obtained in a two steps. First a micellar aqueous solution of (11‐(acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB) and NIPAM is exposed to 60Co‐gamma irradiation, and a thermoresponsive copolymer gel is obtained. Second, DSHA is included by shrinking the gel at 50 °C and subsequent reswelling in an aqueous solution of DSHA disodium salt at 20 °C. Reswelling is accompanied by electrostatic adsorption of DSHA dianions at the positively charged AUTMAB headgroups replacing the bromide ions. Gels containing trans‐DSHA are transparent yellow at room temperature (λmax = 370 nm), while gels containing cis‐rich DSHA are orange (λmax = 460 and 330 nm). Energy dispersive X‐ray measurements indicate that 41% of the bromide ions are exchanged if trans‐DSHA is used for adsorption, and only 7.5% if cis‐DSHA is used. The incorporation of DSHA lowers the lower critical solution temperature (LCST) from 34 to 32 °C. Below the LCST, DSHA can be switched from the trans‐ to the cis‐rich state and vice versa upon irradiation with UV (λ = 366 nm) or visible light (λ ≥ 450 nm). Above the LCST no photoreaction takes place. 相似文献
403.
Sotiria Kripotou Polycarpos Pissis Yuri V. Savelyev Ludmila P. Robota Tamara V. Travinskaya 《Journal of Macromolecular Science: Physics》2013,52(1):86-110
Differential scanning calorimetry (DSC), broadband dielectric relaxation spectroscopy (DRS), and thermally stimulated depolarization current (TSDC) techniques were employed to investigate glass transition and polymer dynamics in nanocomposites of polyurethane (PU) and organically modified montmorillonite (MMT) (weight fraction 0%–15%) prepared by solution casting. The PU matrix was obtained from oligo(oxytetramethylene glycol) of molar mass 1000 g/mol, 4,4′-diphenylmethane diisocyanate and 1,1-dimethylhydrazine as chain extender. Wide-angle X-ray scattering confirmed the formation of partly exfoliated structures at low MMT content. DSC, DRS, and TSDC show, in agreement with each other, that a fraction of polymer makes no contribution to the glass transition and to the corresponding α relaxation, whereas the rest exhibits similar glass transition dynamics as the pure matrix. This fraction of immobilized polymer reaches a maximum at about 5 wt% MMT. Effects of MMT on the microphase-separated structure of PU are negligible, as indicated by the study of glass transition and interfacial dielectric polarization/relaxation. No effects of MMT on the local, secondary γ and β relaxations were observed. Mechanical properties show a maximum improvement at about 5 wt% MMT, in good correlation with morphology and dynamics. 相似文献
404.
Stephan Schulz Prof. Dr. Tamara Eisenmann Ulrich Westphal Sarah Schmidt Ulrich Flörke 《无机化学与普通化学杂志》2009,635(2):216-220
The monomeric β‐diketiminate zinc complex (Mes)NacNacZnMe 1 (MesNacNac = {[2,6‐(2,4,6‐Me3‐C6H2)N(Me)C)]2CH}) was obtained in almost quantitative yield from the reaction of ZnMe2 with (Mes)NacNacH. Reaction of 1 with either Me3NHCl or a solution of HCl in Et2O yielded (Mes)NacNacZnCl 2 , whereas (Mes)NacNacZnI 3 was obtained from the reaction of 1 with I2. 1 – 3 were characterized by elemental analyses, mass and multinuclear (1H, 13C{1H}) NMR spectroscopy, 3·THF also by single crystal X‐ray analysis. 相似文献
405.
Zaliya A. Sabirova Marianna M. Danilova Nikolai A. Kuzin Valerii A. Kirillov Vladimir I. Zaikovskii Tamara A. Krieger 《Reaction Kinetics and Catalysis Letters》2009,97(2):363-370
XRD, mercury porosimetry, low-temperature nitrogen adsorption and electron microscopy were used to study peculiarities of
the formation of reinforced composite nickel catalysts. The catalysts were prepared by sintering powdered metallic nickel
with a supported nickel catalyst (GIAP-3 or NIAP-18) applied to a reinforcing stainless steel gauze. It was found that a metal
matrix, in the pores of which supported catalyst particles were distributed, was formed in the composite catalysts. The NIAP-18-based
catalyst exceeded the GIAP-3-based catalyst in activity toward the methane steam reforming. The NIAP-18-based catalyst was
as active as the Cr2O3-doped NIAP-18-based catalyst, but showed a worse coke-resistance. A chromium oxide additive increased the activity of the
GIAP-3-based catalyst. 相似文献
406.
Elena V. Ovchinnikova Galina Ya. Popova Tamara V. Andrushkevich 《Reaction Kinetics and Catalysis Letters》2009,96(1):91-100
A kinetic model for the β-picoline oxidation over vanadia-titania catalyst is presented. The model covers the reaction mechanism,
temperature dependences and a system of kinetic equations. The activation energies and constants in these equations are calculated. 相似文献
407.
Hamilton TD Papaefstathiou GS MacGillivray LR 《Journal of the American Chemical Society》2002,124(39):11606-11607
A linear template is used to direct the synthesis of a "head-to-head" tetrapyridine in the solid state, which, in a second step, assembles with a transition-metal-ion to form a polyhedral metal-organic host with a structure that conforms to a trigonal antiprism. The application of the linear template is reminiscent of the synthetic strategy of nature. 相似文献
408.
Jacob Bekenstein's identification of black hole event horizon area with entropy proved to be a landmark in theoretical physics. In this paper we trace the subsequent development of the resulting generalized second law of thermodynamics (GSL), especially its extension to incorporate cosmological event horizons. In spite of the fact that cosmological horizons do not generally have well-defined thermal properties, we find that the GSL is satisfied for a wide range of models. We explore in particular the case of an asymptotically de Sitter universe filled with a gas of small black holes as a means of casting light on the relative entropic worth of black hole versus cosmological horizon area. We present some numerical solutions of the generalized total entropy as a function of time for certain cosmological models, in all cases confirming the validity of the GSL. 相似文献
409.
Tamara Elzein Maurice Brogly Gilles Castelein Jacques Schultz 《Journal of Polymer Science.Polymer Physics》2002,40(14):1464-1476
The structural properties and interfacial organization of polyamides adsorbed as thin films were investigated. Polarization‐modulation infrared reflection–absorption spectroscopy was used first to identify the crystalline structure of adsorbed layers and to reveal the conformation and orientation of adsorbed chains. The influence on the structure and molecular orientation of the number of carbon atoms in the aliphatic chain of the diacid part was investigated (PA 66, 610, and 612). The effect of the substrate surface chemistry was also examined. Gold substrates are either inert or functionalized with OH groups. Grafting of the OH functions did not affect the orientation of chains that apparently lay rather parallel to the interface, whereas the crystalline morphology was dependent on the substrate chemical functionality. Knowledge of the structure and orientation of chains adsorbed at an interface was of fundamental importance for the prediction of adhesive strength, that is, the final performance of these latter depended strongly on the properties of the interface formed between the solids brought into contact. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1464–1476, 2002 相似文献
410.
The effect of thermal treatment on the thermodynamic properties and structure of a nematic thermotropic main chain polymer with mesogenic groups containing 3,3'-biphenylene units and octamethylene flexible spacers (BF8) has been studied by DSC and X-ray scattering. We have found that BF8 samples do not crystallize even on very slow cooling from the isotropic state, and possessed a glassy nematic structure at room temperature. The strong influence of the cooling rate on both the enthalpy of the nematic-isotropic transition and the rise of specific heat at the glass transition for BF8 samples was observed. It was attempted to explain this result in terms of the improvement of the nematic structure during cooling. 相似文献