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131.
On the plastic deformation of bulk syndiotactic polypropylene 总被引:1,自引:0,他引:1
The plastic deformation of syndiotactic polypropylene (sPP) bulk samples has been investigated. A structural comparison of
the initial states before and after plastic deformation by necking is carried out by X-ray diffraction observations. Independent
of the initial states (amorphous, semi-crystalline with different crystal phases), only the planar all-trans crystal form of sPP is present in the deformed samples after necking. Form these results, molecular mechanisms of the plastic
deformation in the neck zone of semi-crystalline polymers will be discussed.
Received: 11 February 1997 Accepted: 15 August 1997 相似文献
132.
A challenge in free energy calculation for complex molecular systems by computer simulation is to obtain a reliable estimate within feasible computational time. In this study, we suggest an answer to this challenge by exploring a simple method, overlap sampling (OS), for producing reliable free-energy results in an efficient way. The formalism of the OS method is based on ensuring sampling of important overlapping phase space during perturbation calculations. This technique samples both forward and reverse free energy perturbation (FEP) to improve the free-energy calculation. It considers the asymmetry of the FEP calculation and features an ability to optimize both the precision and the accuracy of the measurement without affecting the simulation process itself. The OS method is tested at two optimization levels: no optimization (simple OS), and full optimization (equivalent to Bennett's method), and compared to conventional FEP techniques, including the widely used direct FEP averaging method, on three alchemical mutation systems: (a) an anion transformation in water solution, (b) mutation between methanol and ethane, and (c) alchemical change of an adenosine molecule. It is consistently shown that the reliability of free-energy estimates can be greatly improved using the OS techniques at both optimization levels, while the performance of Bennett's method is particularly striking. In addition, the efficiency of a calculation can be significantly improved because the method is able to (a) converge to the right answer quickly, and (b) work for large perturbations. The basic two-stage OS method can be extended to admit additional stages, if needed. We suggest that the OS method can be used as a general perturbation technique for computing free energy differences in molecular simulations. 相似文献
133.
134.
D. Levy F. Del Monte X. Quintana J.M. Otón 《Journal of Sol-Gel Science and Technology》1997,8(1-3):1063-1066
Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass
dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals;
no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative
study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid
crystal microdroplets is presented. 相似文献
135.
X. Bokhimi A. Morales E. Ortíz T. López R. Gómez J. Navarrete 《Journal of Sol-Gel Science and Technology》2004,29(1):31-40
Sol-gel titania was sulfated by using sulfuric acid as hydrolysis catalyst, or by impregnating with ammonium sulfate fresh samples prepared with nitric acid or ammonium hydroxide as hydrolysis catalyst. Samples were characterized with X-ray powder diffraction, infrared spectroscopy, thermogravimetry and atomic absorption spectroscopy. Sulfate ions were found anchored to brookite and anatase phases, because they have short O—O atomic bond lengths slightly larger than the largest O—O bond length of sulfate ion. Since the shortest O—O atomic bond in anatase is smaller than the one in brookite, the sulfate ions are then less deformed when they are anchored to anatase, and consequently more stable. Therefore when the sample temperature is raised, the brookite with sulfate ions was transformed mainly to anatase and not into rutile, which is the most probably transformation when these ions are not involved. Sulfate ions also hindered anatase and brookite crystallite growing and stabilized the crystalline structure of anatase. When the sulfate ions are lost the crystalline anatase phase is transformed into rutile, leaving a large number of vacancies that favored atom diffusion and consequently the growing of rutile crystallites. The crystalline evolution of the samples as a function of the annealing temperature is almost independent of the sulfating method. 相似文献
136.
137.
Yuichi Michiue 《Journal of solid state chemistry》2006,179(8):2578-2583
Phase relations of rutile, freudenbergite, and hollandite structures were examined in the pseudobinary system NaCrO2-TiO2 (i.e., NaxCrxTi8−xO16) at 1350 °C. The hollandite structure was obtained in the composition range 1.7?x?2.0. The symmetry of the samples at room temperature was tetragonal for x=1.7 and 1.75, and monoclinic for x=1.8 and above. Single crystals of monoclinic hollandite Na2Cr2Ti6O16 were grown and the structure refinement has been carried out using an X-ray diffraction technique. The space group was I2/m and cell parameters were a=10.2385(11), b=2.9559(9), c=9.9097(11)Å, and β=90.545(9)° with Z=1. The Na ion distribution in the tunnel was markedly deformed from that in the tetragonal form. It was suggested that Cr/Ti ratios were different between the two framework metal sites. 相似文献
138.
ELECTROCHEMICAL POLYMERIZATION OF ANILINE IN PHOSPHORIC ACID AND THE PROPERTIES OF POLYANILINE 总被引:1,自引:0,他引:1
The behavior of the electrochemical polymerization of aniline in a weak acid, phosphoric acid, is very similar to that in strong acids, i.e. its polymerization rate increases quickly with the electrolysis time. The FTIR spectra of polyaniline samples synthesized in phosphoric acid indicate that the counter ion H2PO4^- is present in both the oxidized form and the reduced form of polyaniline. The counter ion plays an important role in adjusting the pH value at the electrode surface of polyaniline during the oxidation and reduction processes. As a result, a pair of redox peaks still appear in cyclic voltammograms of polyaniline in a solution of sodium sulfate of pH 5.5 and in a solution of NaH2PO4 of pH 7.0,respectively, at low potential scan rate; and the color of polyaniline film also changes with applied potential at pH 7.0. Thus,the pH region for the electrochemical activity and the electrochromism of polyaniline is extended to pH 5.5 for a solution of sodium sulfate and to pH 7.0 for a solution of NaH2PO4. The conductivity of polyaniline is 3.3 S cm^-1, depending on the concentration of phosphoric acid used in the stage of polymerization of aniline. The result of elemental analysis of polyaniline is presented here. 相似文献
139.
Jungui DaiShujun Zhang Jun-ichi SakaiJiao Bai Yoshiki OkuMasayoshi Ando 《Tetrahedron letters》2003,44(5):1091-1094
Three C-14 oxygenated taxanes, 2α,5α,10β,14β-tetraacetoxytaxa-4(20),11-diene (1), 2α,5α,10β-triacetoxy-14β-(2-methylbutyryloxy)taxa-4(20),11-diene (2), and yunanaxane (3), major products of callus cultures of Taxus spp., were regio- and stereoselectively hydroxylated at the 7β position by a fungus, Absidia coerulea IFO 4011. Intriguingly, when 1 was co-administered with β-cyclodextrin and incubated with the fungus cell cultures, three other compounds 5α,9α,10β,13α-tetraacetoxytaxa-4(20),11-dien-14β-ol (7), 5α,9α,10β,13α-tetraacetoxytaxa-4(20),11-dien-1β-ol (8) and 5α,9α,10β,13α-tetraacetoxy-11(15→1) abeotaxa-4(20),11-dien-15-ol (9) were obtained. 相似文献
140.
分光光度法同时测定中草药中的钼和铜 总被引:2,自引:2,他引:2
本文建立了在混合显色剂(PF+PAN)的胶束体系中,利用分光光度法同时测定中草药中的钼和铜。实验表明:在混合体系中,钼量在0~10μg/25mL,铜量在0~50μg/25mL的范围内符合比尔定律,ε′Mo=9.2×104L·mol-1·cm-1;ε′Cn=1.5×104L·mol-1·cm-1。该法用于中草药样品的分析,结果满意,回收率可达92~111%。 相似文献