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101.
102.
T. Ohta M. Nonomura 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):57-68
We study the domain morphology in a phase separated state of diblock copolymer-homopolymer mixtures. In the situation that
one of the blocks of copolymers is incompatible with homopolymers, formation of a bilayer membrane of block copolymers is
shown to be possible in the matrix of homopolymers. Starting with the free energy functional in terms of the local volume
fractions of each monomer, we derive the bending and curvature rigidities in the Helfrich free energy for a membrane. It is
found that the curvature modulus is negative only in a limited region of the parameters, where a closed shape of a membrane
like a vesicle is possibly formed. We establish a method to calculate the rigidities without a molecular picture in a consistent
way with the field theoretic model free energy. Stability of a bilayer membrane compared with micelles is also investigated.
Received: 22 July 1997 / Received in final form: 1 December 1997 / Accepted: 22 January 1998 相似文献
103.
Like many separation processes, ultrafiltration and reverse osmosis are often compromised by concentration polarization. Such polarization can be mitigated by static mixers and other flow barriers placed as spacers next to the membrane surface. These spacers can be shaped like ladders, herringbones, and helices. The effect of these spacers can be successfully predicted without adjustable parameters from extensions of the Lévêque equation. The predictions are in agreement with results of computational fluid mechanics and with electrochemical experiments. They supply a tool for optimizing spacer design. 相似文献
104.
105.
Analytical Solution of Compression,Free Swelling and Electrical Loading of Saturated Charged Porous Media 总被引:2,自引:0,他引:2
van Meerveld J. Molenaar M. M. Huyghe J. M. Baaijens F. P. T. 《Transport in Porous Media》2003,50(1-2):111-126
Analytical solutions are derived for one-dimensional consolidation, free swelling and electrical loading of a saturated charged porous medium. The governing equations describe infinitesimal deformations of linear elastic isotropic charged porous media saturated with a mono-valent ionic solution. From the governing equations a coupled diffusion equation in state space notation is derived for the electro-chemical potentials, which is decoupled introducing a set of normal parameters, being a linear combination of the eigenvectors of the diffusivity matrix. The magnitude of the eigenvalues of the diffusivity matrix correspond to the time scales for Darcy flow, diffusion of ionic constituents and diffusion of electrical potential. 相似文献
106.
J.S. Vrouwenvelder J.A.M. van Paassen J.M.C. van Agtmaal M.C.M. van Loosdrecht J.C. Kruithof 《Journal of membrane science》2009
The relation between biofouling and membrane flux in spiral wound nanofiltration and reverse osmosis membranes in drinking water stations with extensive pretreatment such as ultrafiltration has been studied. The flux – water volume flowing through the membrane per unit area and time – is not influencing the development of membrane biofouling. Irrespective whether a flux was applied or not, the feed spacer channel pressure drop and biofilm concentration increased in reverse osmosis and nanofiltration membranes in a monitor, test rigs, a pilot scale and a full-scale installation. Identical behavior with respect to biofouling and feed channel pressure drop development was observed in membrane elements in the same position in a nanofiltration installation operated with and without flux. Calculation of the ratio of diffusive and convective flux showed that the diffusive flux is considerably larger than the convective flux, supporting the observations that the convective flux due to permeate production is playing an insignificant role in biofouling. Since fouling occurred irrespective of the actual flux, the critical flux concept stating that “below a critical flux no fouling occurs” is not a suitable approach to control biofouling of spiral wound reverse osmosis and nanofiltration membranes. 相似文献
107.
Effects of polymerization conditions on hydrophilic groups in aromatic polyamide thin films 总被引:1,自引:1,他引:0
For polyamide used in reverse osmosis (RO) membranes, the content of pendant acid groups is critical to its performance. In this work, FTIR was used to analyze the acid contents in the polyamide films prepared via interfacial polymerization of trimesic acid trichloride (TMC) in hexane and 1,3-phenylenediamine (MPDA) in water, and the effects of reaction conditions, including monomer concentrations, time, and temperature, were studied. It was found that more pendant acid groups are present in the polyamide film at higher TMC concentrations or lower MPDA concentrations, and longer reaction times and lower temperatures also favor the formation of the free acids. These results can be explained by the monomer diffusion in the interfacial polymerization process. This work may help the design and fabrication of RO membranes with different hydrophilicity and target performance. 相似文献
108.
Reverse osmosis membrane treatment of acidic etchant wastewater: Effect of neutralization and polyelectrolyte coating on nitrate removal 总被引:1,自引:0,他引:1
The removal of nitrate from mixed acid etchant (MAE) wastewater was investigated by neutralization, followed by reverse osmosis (RO) membrane filtration. The coating of a RO membrane was conducted using polyacrylic acid (PAA) in order to enhance the removal of nitrate from the MAE wastewater. The addition of KOH, for the neutralization of the MAE wastewater, was most effective in terms of solid–liquid separation. Double RO filtrations, with crossflow and stirred-flow units, were examined in terms of nitrate rejection and membrane permeability. The Donnan exclusion, due to change in the solution pH, played an important role in nitrate rejection. As a result, RO filtration, at a moderate acidic pH level (e.g., pH 4), provided greater nitrate rejection than that at neutral or alkaline pH levels. The Donnan effect was associated with acetic acid present in MAE wastewater, since it could deprotonate to acetate with a negative charge. Improvement in nitrate rejection occurred with the PAA coating of the original RO membrane. This is because of the enhanced electrostatic repulsion of the nitrate by the carboxyl groups on the coated membrane surface, although the flux declined with the PAA coatings. The effect of charge repulsion was more obvious in the second pass of RO filtration where the ionic strength was relatively low. The increase in nitrate rejection leveled off with a PAA dosage of 0.262 mg/cm2 of the membrane, so further coating beyond this level should be prevented. 相似文献
109.
An analysis of the phenomenon of osmosis within the lattice gas model is presented. The model considered is a two-species version of the Frisch-Hasslacher-Pomeau model with rest particles and a semipermeable membrane which is implemented as a boundary that blocks one species, but lets the other pass freely. In this way the equilibrium between a pure and a mixed subsystem can be studied. Analytic expressions for both the pressure difference and the fluctuations of this quantity are obtained from the entropy function for the lattice gas, and we find that these results are in good agreement with those obtained from simulation. The osmotic flow across the membrane is also studied. We characterize the concentration boundary layer, and an analytic expression for the osmotic permeability as a function of porosity is compared with results from simulations. 相似文献
110.