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81.
SHEN Yu-Feng WANG Qing-Hai ZHU Dao-Qian ZHOU Liang-Mo Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian Liaoning China 《中国化学》1994,12(2):129-137
The study on retention behavior in supercritical fluid chromatography (SFC) is necessary to understand the mechanism of the various interactions in SFC. The retention of SFC in carboxylic acid methyl ester/polymethylsiloxane/CO2 system was studied systematically and the retention behavior of this kind of compounds under various typical operation conditions was described using the method of an alternative unified theory of chromatographic retention. The results illustrated that expression: Ink.= a + b/T + cp + dp/T + ep2/T can be used to describe quantitatively the retention behavior of carboxylic acid methyl ester/polymethylsiloxane/CO2 system in the ranges of reduced density from 0.549 to 1.411. It was also found that the entropy of solute in stationary phase is dependent on the density of supercritical fluid (SF) under typical operating conditions of SFC. 相似文献
82.
Chiral monomer (M1 ), mesogenic and non-mesogenic crosslinking agents (C1 and C2 ), and the corresponding liquid crystalline elastomers (P1 and P2 series), have been synthesised. Their chemical structures have been characterised by Fourier transform infrared or 1H nuclear magnetic resonance and their phase behaviour investigated by differential scanning calorimetry, polarising optical miscoscopy, thermo-gravimetric analysis (TGA) and X-ray diffraction. The effect of the crosslinking unit on the phase behaviour of the elastomers has been studied. M1 showed a cholesteric oily streak and focal conic texture. C2 exhibited a nematic enantiotropic thread-like and schlieren texture, and a monotropic fan-shaped texture in the SA phase. Due to the introduction of the mesogenic crosslinking unit, elastomers, P2-1 ?P2-5 , exhibited a cholesteric phase, while elastomers, P1-1 ?P1-4 , derived from a non-mesogenic crosslinking unit, exhibit a SA phase. As the content of the crosslinking unit increased, the T g of the P1 series initially decreased and then increased, and the T i of the series decreased. In the P2 series the T g increased, but the T i initially increased and then decreased. TGA confirmed that all the elastomers had improved thermal stability. 相似文献
83.
The crystalline behavior of urethane substitute polydiacetylene was studied by using pohrized light and electron microscopy. The lamellar morphological structure was observed in the crystallized films. The thickness of lamellae is about 300A, being independent of the crystalline temperature. But the size and density of lamellae were dependent on the crystallization temperature. If the molten film was sheared during the crystallzation process the oriented lamellae grew with their long axes perpendicular to the direction of shear and the chain direction was normal to the lamellar surface. 相似文献
84.
Sophie Peeterbroeck Fouad Laoutid Benjamin Swoboda Jos‐Marie Lopez‐Cuesta Nicolas Moreau Janos B. Nagy Michaël Alexandre Philippe Dubois 《Macromolecular rapid communications》2007,28(3):260-264
Nanocomposites based on an ethylene–vinyl acetate copolymer (27 wt.‐% vinyl acetate) and multiwall carbon nanotubes (MWNTs) have been prepared by melt blending and their thermal degradation and flame retardant properties have been evaluated. Special attention has been paid to the influence of the nanotube nature on the flammability properties and more particularly on the time to ignition (TTI) as measured by cone calorimetry. It has been shown that there is a strong influence of the nature of carbon nanotubes on the fire behaviour of the composites, especially previous MWNTs crushing proved to substantially delay the TTI while maintaining much reduced heat release rate (HRR). Such a remarkable behaviour might be explained by the chemical reactivity of radical species present at the surface/extremities of crushed MWNTs during the combustion process.
85.
On the basis of a better analytical exploitation of acid-induced cloud point approach, a systematic study on the phase behaviour of acid aqueous solutions of anionic surfactants and factors affecting anionic surfactant-mediated extractions was performed. The anionic surfactants investigated were alkylsulphonates (ASS) with alkylchain lengths comprised between 8 and 16 carbon atoms. The critical hydrochloric acid concentration (minimal acid concentration required to separation in two liquid phases) was found to increase as alkylchain length of the anionic surfactant increased from 10 to 14. Non-acid-induced liquid-liquid phase separation was observed for sodium octanesulphonate (SOS) or sodium hexadecyl sulphonate (SHS) in the hydrochloric concentration range 0-10 M. Acid aqueous solutions of sodium decylsulphonate (SDeS) and sodium dodecylsulphonate (SDoS) separated into two liquid phases at temperatures ranging between 10 and 80 °C, while temperatures >35 °C were required for sodium tetradecylsulphonate. The influence on extraction efficiency and concentrating ability of experimental variables such as hydrophobicity and concentration of surfactant, nature and concentration of analyte, hydrochloric acid concentration, time and temperature of extraction and time of equilibration and centrifugation was examined. Advantages provided by anionic surfactant-mediated extractions over the use of non-ionic surfactants (cloud point extractions) are discussed. 相似文献
86.
C. DurioA. Daidouh N. ChouaibiC. Pico M.L. Veiga 《Journal of solid state chemistry》2002,168(1):208-216
New sodium orthophosphates of general formula Na2M3(PO4)3 belonging to the alluaudite-type structure have been synthesized and characterized by neutron and X-ray powder diffraction. The nature of the M3 elements (M3=GaMn2, GaCd2, InMn2 and FeMnCd) was chosen in order to analyze their influence on electrical and magnetic properties. The conductivity of these materials was measured by the complex impedance method and the transport mechanism was studied from complex permittivities and modulus formalism. Electrical results including charge/discharge experiments showed two main behaviors: GaCd2 and FeMnCd behave as purely ionic conductors whereas GaMn2 and InMn2 are mixed ionic-electronic conductors. The magnetic susceptibility data reveal the antiferromagnetic behavior of FeMnCd, InMn2 and GaMn2, with a weak ferromagnetic transition at low temperatures. 相似文献
87.
Hui‐Ru Chen Wen‐Wen Zhang 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(11):1079-1082
The title CdII coordination framework, [Cd(C15H8O5)(H2O)]n or [Cd(bpdc)(H2O)]n [H2bpdc is 2‐(4‐carboxybenzoyl)benzoic acid], has been prepared and characterized using IR spectroscopy, elemental analysis, thermal analysis and single‐crystal X‐ray diffraction. Each CdII centre is six‐coordinated by two O atoms from one 2‐(4‐carboxylatobenzoyl)benzoate (bpdc2−) ligand in chelating mode, three O‐donor atoms from three other bpdc2− anions and one O atom from a coordinated water molecule in an octahedral coordination environment. Two crystallographically equivalent CdII cations are bridged by one O atom of the 2‐carboxylate group of one bpdc2− ligand and by both O atoms of the 4‐carboxylate group of a second bpdc2− ligand to form a binuclear [(Cd)2(O)(OCO)] secondary building unit. Adjacent secondary building units are interlinked to form a one‐dimensional [Cd(OCO)2]n chain. The bpdc2− ligands link these rod‐shaped chains to give rise to a complex two‐dimensional [Cd(bpdc)]n framework with a 4,4‐connected binodal net topology of point symbol {43.62.8}. The compound exhibits a strong fluorescence emission and typical ferroelectric behaviour in the solid state at room temperature. 相似文献
88.
Yoann Lalatonne Farah Benyettou Nicole Lièvre Marc Lecouvey Laurence Motte 《Journal of magnetism and magnetic materials》2009,321(10):1653-1657
Magnetic nanoparticles differing by their size have been synthesized to use them for multiparametric testing, based on their differing magnetic properties. The nanoparticle has two essential roles: to act as a probe owing to its specific magnetic properties and to carry on its surface precursor groups for the covalent coupling of biological recognition molecules, such as antibodies, nucleic acids. A totally unique, newly patented, method has been used to characterize magnetic signatures using the MIAplex technology. The MIAplex reader, developed by Magnisense, measures the non-linear response of the magnetic labels when they are exposed to a multi-frequency alternating magnetic field. This specific signature based on d2B(H)/dH2 was correlated to other more conventional magnetic detection methods (superconducting quantum interference devices (SQUID) and Mössbauer). 相似文献
89.
K.D. Cherednichenko 《Journal of the mechanics and physics of solids》2010,58(5):798-809
Using an averaging procedure for large ensembles of dislocations, a basic but mathematically non-trivial modelling framework is developed for the transport of dislocation densities in a macroscopically homogeneous and isotropic film of a crystalline solid subjected to uniform shear. It has the form of a system of nonlinear, non-local partial differential equations of the first order with a source-type right-hand side. The solution to this system is studied numerically, and the associated average stress is evaluated as a function of time. The resulting stress-strain relations exhibit a size effect similar to those that previously motivated strain-gradient plasticity theories. 相似文献
90.
We investigate the small ball problem for d-dimensional fractional Brownian sheets by functional analytic methods. For this reason we show that integration operators of Riemann–Liouville and Weyl type are very close in the sense of their approximation properties, i.e., the Kolmogorov and entropy numbers of their difference tend to zero exponentially. This allows us to carry over properties of the Weyl operator to the Riemann–Liouville one, leading to sharp small ball estimates for some fractional Brownian sheets. In particular, we extend Talagrand's estimate for the 2-dimensional Brownian sheet to the fractional case. When passing from dimension 1 to dimension d2, we use a quite general estimate for the Kolmogorov numbers of the tensor products of linear operators. 相似文献