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101.
The kinetic effect of the phase inversion process on the membrane morphology is explored, with emphasis on the diffusion coefficient of the nonsolvent as a measure of the solvent/nonsolvent exchange rate. The diffusion coefficient is closely related to the nonsolvent tolerance of the polymer solution, which was estimated from a pseudo-ternary phase diagram of the following system: polymer: polysulfone; solvent system: a mixture of the solvent 1-methyl-2-pyrrolidinone and a solvent additive (formic acid, water or ethanol); and nonsolvent: ethanol. Regardless of the kind of solvent additive employed, when the diffusion coefficient of the nonsolvent is high for a given gelation medium, then the membrane consists of a smooth, defect-free surface and macrovoid-free cross section, and is highly permeable to oxygen. However, using a polymer solution with a low diffusion coefficient results in a membrane of a rather defective morphology. Therefore, it is concluded that the diffusion coefficient of the nonsolvent is a crucial parameter in controlling membrane morphology. 相似文献
102.
Monodisperse, reactive hydrogel microspheres were prepared by precipitation polymerization ofp-nitrophenyl acrylate (NPA) with acrylamide, methacrylic acid, and methylenebisacrylamide in ethanol. The size of microspheres was controlled by the monomer ratio. Some fraction of reactive ester decomposed during the polymerization. The reactive hydrogel microspheres were converted to amphoteric ones by the reaction of NPA units with diamine. The isoelectric point of the amphoteric microspheres was around 4.0, but it was different from the pH at which the microspheres have the minimum size or the most shrunken state. This was attributed to the uneven distribution of induced amine groups. 相似文献
103.
Summary A procedure to include a way for forecasting the precipitation occurrence in the air mass trajectory computation for climatological
studies in order to compute the wet deposition of airborne pollutants is presented. It is based on a technique proposed by
Moscoet al., Riv. Meteorol. Aeronaut.,33, 229 (1973). Its performance is tested comparing the forescen occurrence of either precipitation or no precipitationversus the actual one for two stations, Parma and Vipiteno, for a period of four years. In more than 80% of the cases the forecasting
was correct. 相似文献
104.
105.
The influence of concentration, ageing and pH of the gel medium on the periodic precipitation of cobalt oxinate in agar gel
is reported. The results are explained on the basis of Shinohara’s revised flocculation theory. The flocculation value (F) increases with increase in the gel concentration whereas it decreases with increase in ageing and pH of the gel. The raise
in temperature of the gel increases the solubility of the sparingly soluble substance and hence theF value. The effect of additives on the periodic precipitation of cobalt (II) oxinate is reported. 相似文献
106.
An elongational flow technique was used to determine the effect of counterions on the chain conformation of polyelectrolyte molecules in solution, by means of the extensibility of the chains in the flow field. It is demonstrated that adding excess cations of seven low molecular weight salts, NaCl, CaCl2, BaCl2, SrCl2, MgCl2, AlCl3, and SnCl4, to a very dilute solution of fully sulphonated polystyrene (NaPSS) reduces the extensibility of the chains, that is, the facility by which a chain can be extended to varying degrees, an effect associated with chain contractions. In the case of multivalent counterions, these contractions, which with monovalent counterions are primarily due to screening of charges by excess counterions, are greatly enhanced, which we attribute to the formation of intramolecular ionic bridges. When, in the case of multivalent counterions, the polymer concentration is increased, in inversion of the effect, namely increase in chain extensibility on addition of ions, is observed. We attribute this latter effect to the ionic bridges becoming increasingly intermolecular, leading to effectively large molecules, and eventually to a gel. All these effects were accentuated with increase in valency. They could also be accompanied by precipitation which were of two kinds: one due to formation of insoluble ionic associations and a second attributable to enhanced hydrophobic interaction within the contracted chain itself. © 1994 John Wiley & Sons, Inc. 相似文献
107.
为了研 究中尺度城市对降水 的影响,本文利用一个三维数值棋式,对 下垫面 在气旋暴雨过程中的作用进行 了数值棋拟.较详细地研 究了下垫 面性质不均匀造成的边界层结 构特征和局地环流.棋式结果揭示出中尺度城市可 引起不稳定层结、风场和垂 直环流的变 化,从而影 响降水分布. 相似文献
108.
The results of electrical conductivity measurements in heavily doped RbCl:CoCl2 crystals with 2500 and 6000 ppm of cobalt are being reported in this paper. The different regions of the conductivity plots
for the crystals with the two concentrations of cobalt have been explained and relevant energy parameters determined. The
crystals with 6000 ppm of cobalt have been found to contain two types of precipitates one of these being of the same type
as that existing in RbCl crystals with 2500 ppm of cobalt while the other being of a different composition.
Further, it has been found that the crystals appear blackened after heating during measurements. The blackening has been attributed
to the expulsion of cobalt from the bulk of the crystal which forms an oxide at the surface. 相似文献
109.
Zoltán Aigner Ingrid Bencz Michael Kata 《Journal of inclusion phenomena and macrocyclic chemistry》1994,20(3):241-252
The incidence of genetic lipoprotein disorders, or hyperlipoproteinaemia, is currently increasing. Examinations were carried out on the hyperlipoproteinaemic drug fenofibrate and various cyclodextrin derivatives were applied to increase the solubility of this drug. Numerous products with several compositions (drug: CD mole ratio=2:1, 1:1, 1:2 or 1:3) were studied and three preparation methods (powder mixing, kneading and precipitation) were used. In vitro drug liberation and membrane diffusion examinations revealed compositions suitable for the preparation of a capsule dosage form (1:2 and 1:3 physical mixtures).Dedicated to Dr. Béla Selmeczi, university professor, with the best wishes for his 65th birthday. 相似文献
110.
Yu. I. Stozhkov J. Zullo I. M. Martin G. Q. Pellegrino H. S. Pinto G. A. Bazilevskaya P. C. Bezerra V. S. Makhmutov N. S. Svirzevsky A. Turtelli 《Il Nuovo Cimento C》1995,18(3):335-341
Summary The changes of rainfall values during great Forbush decreases recorded by the low-latitudinal neutron monitor of Huancayo
(47 events from 1956 through 1992) were examined. The data on precipitations were taken from the State of S?o Paulo and from
the Amazonian region, Brazil. As a rule, the data from more than 50 meteorological stations were used for each events. The
main result is the following: during strong decreases of cosmic-ray flux in the atmosphere (great Forbush decreases) the precipitation
value is decreased. The effect of rainfall changes is seen more distinctly if wet seasons are considered. 相似文献