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Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains. Copyright 2000 Academic Press. 相似文献
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Eugen Jóna Marian Koman Anton Sirota 《Journal of inclusion phenomena and macrocyclic chemistry》1998,30(1):1-12
The stoichiometry and spectral properties of [Ni(4-Etpy)4(NCS)2]nG clathrates have been studied where n = 2 for G = 1-BrN (N = naphthalene), n = 1 or 2 for G = 1-MeN, and n = 0.5 for 2-MeN and 2-BrN. The complexes under study show electronic absorption spectra typical of an octahedral environment of the Ni(II) central atom. The differences found in IR spectra for the (CN) and (Ni–-NNCS) vibrations are discussed. The crystal structure of [Ni(4-Etpy)4(NCS)2]1-MeN was determined by X-ray diffraction and refined to R = 0.0586. Discrete non-centrosymmetric [Ni(4-Etpy)4(NCS)2] molecules form layers of a host structure and the space between the layers is occupied by 1-MeN. The relationship between interatomic distances in the host complex of similar clathrates are discussed. 相似文献
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de Farias RF de Souza JM de Melo JV Airoldi C 《Journal of colloid and interface science》1999,212(1):123-129
The effects exhibited by adsorbed conducting polyaniline on the redox process on a molybdenum oxide surface were studied. Thermogravimetric results indicate a 4% polyaniline deposition. Cyclic voltammograms of the adsorbed polymer on MoO3 show that polyaniline exerts remarkable effects on the molybdenum blue oxidation-reduction process, with oxidation and reduction potentials of 0.33 and 0.18 V, respectively. This effect strongly enhances the electrode response, and can be used as an important tool in qualitative and/or quantitative determinations of molybdenum in solution as well as in any substrate. Copyright 1999 Academic Press. 相似文献
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D. P. Singh B. Sirota S. Talpatra P. Kohli C. Rebholz S. M. Aouadi 《Journal of nanoparticle research》2012,14(4):781
Silver molybdate microrods are self-assembled into micron sized, broom-like and flower-like structures. Our investigations
indicate that through a simple hydrothermal process, large scale production of such structure is possible. Using ammonium
molybdate and silver nitrate solutions as precursors, we were able to show that the self assembled architectures were dependent
on the pH of the starting precursor material. To understand the formation and destructions of the flower-like morphology,
a systematic broad range (from acidic to basic) of pH-controlled experiments were performed and its influence on the structure/microstructure
of synthesized materials was investigated. Scanning electron microscopy studies revealed that the morphology and microstructure
of the products varied significantly by changing pH values from 3 to 8 during mixing of the reactants. pH = 3 and 4 resulted
in the self assembly of monoclinic Ag2(Mo2O7) microrods into broom-like structures, whereas pH = 5 resulted into the flower-like morphology of mixed phase of monoclinic
and triclinic Ag2Mo2O7. We also found that increasing the pH after a certain threshold value (for example pH > 6) resulted in total collapse of
the flower-like morphology. Further increase of the pH to 7 and 8 resulted, the formation of microparticles of Ag2MoO4. A tentative scheme based on the pH-driven evolution of the self-assembly has been given to explain the formation of the
observed heterostructures. Preliminary electrical characterization of thin films of the flower-like structures rendered non-linear
current–voltage (I–V) responses. We also observed a strong hysteresis in the I–V responses of the flower-like structures developed
under high bias conditions. 相似文献
7.
N. N. Sirota V. I. Pavlov A. K. Bogush A. P. Karvay 《Crystal Research and Technology》1981,16(10):1151-1157
The magnetic field effect on conductivity and intensity of the magnetic neutron diffraction reflections as well as magnetization of lanthanum manganite with different crystal lattice distortions in the ferromagnetic-paramagnetic transitions range are investigated. It is shown that in the investigated samples near the paramagnetic-ferromagnetic transition temperature at H = 0 there exists a relatively wide transition range where the magnetic ordering occurs with a relatively small external magnetic field applied. 相似文献
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The Debye-Waller factors and the mean-square dynamics displacements of the Be and O ions in beryllium oxide are obtained from X-ray diffraction powder data over the temperature range from 10 to 720 K for different crystallographic directions. The observed anisotropy of these mean-square displacements is discussed. 相似文献
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