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961.
962.
The membrane composition effect on signal profile of the combined ISE-flow-injection system is examined on the example of Hg(II) flow-injection potentiometric (FIP) detector based on the secondary response to Hg(II) of different thin layer silver chalcogenide membranes, obtained by cathodic electrodeposition at controlled potential. The potential of the electrochemical approach to produce a great diversity of membrane compositions and the possibility for fine tuning of their stoichiometry made it possible to select the stoichiometry with respect to silver (intrinsic defects factor) and the inclusion of dopant (extrinsic defects factor) as the two variable composition parameters. The following membranes have been tested: Ag2Se1−xTex, Ag2Se, Ag2+δSe and Ag2+δSe1−xTex (δ=0.24). The experimental conditions have been varied in a wide range to include four flow-rates (within the 2.5-6 ml min−1 interval), and three typical carrier compositions to which either Ag(I) or Hg(II) have been added as pilot ions. The results obtained in this study show unambiguously that the membrane composition factors are an important figure of merit, the weight of which in some particular cases can be co-measurable with that of the flow manifold factors. A new important information concerning the active role of the “pilot ion” added to the carrier in controlling the rising part of the signal, through changing the membrane response rate order, is also provided. 相似文献
963.
Jonathan A. Brant Kelly M. Johnson Amy E. Childress 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,280(1-3):45-57
Chemical force microscopy (CFM) was used to characterize the chemical heterogeneity of two commercially available nanofiltration and reverse osmosis membranes. CFM probes were modified with three different terminal functionalities: methyl (CH3), carboxyl (COOH), and hydroxyl (OH). Chemically distinct information about the membrane surfaces was deduced based on differences in adhesion between the CFM probes and the membrane surfaces using both traditional atomic force microscopy (AFM) force measurements and spatially resolved friction images. Contact angle titration and streaming potential measurements provided general information about surface chemistry and potential, which largely complemented the CFM analyses, but could not match the accuracy of CFM on the atomic level. Using CFM it was found that both membranes were characterized as chemically heterogeneous. Specifically, membrane chemical heterogeneity became more significant as the scan size approached colloidal or micron-sized dimensions. In many instances, the chemically unique regions, contributing to the overall chemical heterogeneity of the membrane surface, were substantially different in chemistry (e.g., hydrophobicity) from that determined for the surface at large from contact angel and streaming potential analyses. Topographical and corresponding CFM images supports previous adhesion studies finding a correlation between surface roughness and the magnitude of adhesion measured with AFM. However, chemical specificity was also significant and in turn measurable with CFM. The implication of these findings for future membrane development is discussed. 相似文献
964.
Chuangang Fan Wei Liu Zengqiang Deng Yanbo Zuo Chusheng Chen Dongsik Bae 《Journal of membrane science》2007,290(1-2):73-77
In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo0.8Fe0.2O3−δ (SCF) and the SrCo0.8Fe0.1Sn0.1O3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10−6 mol cm−2 s−1 was obtained at 1000 °C and under the oxygen partial pressure gradient of PO2 (h)/PO2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10−6 mol cm−2 s−1 for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity (σe) for SSCF sample appeared with increasing temperature. The second peak value of σe for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice. 相似文献
965.
966.
The preparation of polystyrene-based titanium phosphate membranes at different pressures with varying amounts of material
has been explained. The membrane potentials of inorganic membranes were measured with uni-univalent electrolytes (KCl, NaCl
and LiCl) solution using saturated calomel electrodes (SCEs). The TMS method was used for the evaluation of the effective
fixed charge density of these membranes with increasing pressure, and the surface charge density of membrane appeared to be
increased due to gradually diminution in surface opening channels. The order of surface charge density for electrolytes used
is found to be KCl > NaCl > LiCl. In addition to the effective fixed charge density, distribution coefficient, transport numbers,
charge effectiveness and other related parameters were calculated for characterizing the ion exchange membranes by utilizing
the TMS method. The theoretical prediction is consistent well with the experimental data. The SEM of these membranes at various
pressures has been presented. 相似文献
967.
A. J. Gijsbertsen-Abrahamse A. van der Padt R. M. Boom 《Journal of membrane science》2004,230(1-2):149-159
Cross-flow membrane emulsification has great potential to produce monodisperse emulsions and emulsions with shear sensitive components. However, until now, only low disperse phase fluxes were obtained. A low flux may be a limiting factor for emulsion production on a commercial scale. Therefore, the effects of membrane parameters on the disperse phase flux are estimated. Besides, the effects of these parameters on the droplet size and droplet size distribution are qualitatively described. Wetting properties, pore size and porosity mainly determine the droplet size (distribution). Membrane morphology largely determines the disperse phase flux. As an example, industrial-scale production of culinary cream was chosen to evaluate the required membrane area of different types of membranes: an SPG membrane, an -Al2O3 membrane and a microsieve. Due to the totally different morphologies of these membranes, the fraction of active pores is 1 for a microsieve and is very low for the other membranes. The choice of the optimal membrane did not depend on the production strategy: either to produce large quantities or to produce monodisperse emulsions, the best suitable was a microsieve with an area requirement of around 1 m2. In general, the total membrane resistance should be low to obtain a large disperse phase flux. In contrast, the membrane resistance should be high to obtain monodisperse emulsions when using membranes with a high porosity. 相似文献
968.
969.
Moment theory has been applied to model porous membranes to show that one can place reasonable bounds on the cumulative pore size distribution, the hindered diffusivity or the reflection coefficient of large solutes in a heteroporous membrane by measuring the diffusive permeability to a small solute, the hydraulic permeability and one or two additional transport characteristics. These additional measurements involve either the flux of a small solute at Pe1, the hindered diffusivity of a large solute or the reflection coefficient of a large solute at Peå1. Membrane heteroporosity is incroporated in the predicted bounds without requiring one to make any a priori assumptions about the nature of the pore size distribution. In this paper, the results from calculations performed with different model membranes containing log-normal pore size distributions are reported. A comparison of the results obtained with three different membranes shows that one can distinguish between membranes with the same average pore size but different pore size distributions by measuring either the hindered diffusion coefficient or the reflection coefficient of two different sized solutes. A comparison of the bounds on D and the bounds on σ predicted from different types of transport measurements shows that, under certain conditions, one can place tighter bounds on one transport characteristic by measuring a different one. 相似文献
970.
采用界面缩合聚合方法,合成了一系列主链含硅的芳族聚酰胺,从化学结构与气体透过性能关系的角度研究了此类聚合物均质膜的气体透过性能,结果表明,此类聚合物膜对H2、O2、N2、CO2、CH4的气体透过系数大小顺序符合一般玻璃态聚合物规律;在刚性强的高分子链段中引进柔性基因,可提高聚合物的气体透过系数;高分子主链有较强内旋转能力的聚合物,气体透过系数大;高分子主链的化学结构相同,苯环上带有侧甲基的聚合物有高的气体透过系数;硅原子上带有侧苯基的聚合物,其气体扩散系数大于而溶解系数小于硅原子上携有侧甲基的聚合物.结论为,在刚性高分子主链中引入柔性基团和提高刚性链间隙是增大气体透过含硅聚酰胺膜速率的有利因素. 相似文献