Ref HAL: hal-00426722_v1
DOI: 10.1016/j.desal.2008.03.056
WoS: 000270634100028
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39 Citations
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This work deals with the temperature effect on rejection of neutral and charged solutes by a nanofiltration membrane (Desal 5 DK of GE Osmonics). The experiments were conducted with a tangential Sepa CF cell with a flow velocity equal to 1.27 m/s. The pressure was varied form 5 to 15 bar and the temperature from 12 to 50 degrees C. A low neutral solute concentration (1 g/L) was used in the experiments in order to render solute-solute interactions negligible. The experiments with charged solutes (NaCl, Na2SO4) were conducted at 10(-1)M and 10(-3)M for NaCl and 10(-1) M and 2 x 10(-1)M for Na2SO4. The experimental results: permeate Volume flux density and rejection of four neutral Solutes (glycerin, arabinose, glucose, and sucrose) were analyzed using the hindered transport model and show that both effective pore radius and effective thickness are temperature dependent otherwise there is no agreement between the experimental data and the numerical results. We have found that the effective pore radius increases from 0.58 to 0.67 nm when the temperature increases from 22 to 50 degrees C. A non-monotonic evolution is obtained for the variation of the effective membrane thickness with temperature. The results obtained with charged solutes show a weak dependence on temperature for low concentration salt solutions. For higher concentrations, the rejection decreases when temperature increases in rough conformity with the extended Nernst-Planck transport model, and this decrease can be partly explained by the hindered transport effects already observed for neutral solutes

Ref HAL: hal-00425046_v1
PMID 19497667
DOI: 10.1016/j.jhazmat.2009.04.130
WoS: 000269162000016
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81 Citations
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The wastewaters resulting from different baths of a dyeing factory specialized in denim fabric are collected and treated by an activated sludge plant. This study investigated the coupling of activated sludge treatment with either nanofiltration (NF) or reverse osmosis (RO) to recycle water and reuse it in the process. We first conducted NF experiments with a HL membrane in different configurations: dead end and cross-flow for flat sheets and also in spiral wound form. Results on water permeation and salt rejection show that performances are configuration dependent. Then, for the study of the NF/RO textile wastewater treatment, experiments were conducted with spiral wound membranes in order to be closest to the industrial configuration. After analyzing the removal efficiencies of suspended solids and chemical oxygen demand (COD) of the treatment plant, we conducted NF experiments using an HL2514TF spiral wound membrane preceded by ultrafiltration (UF) treatment. We used as well an RO membrane (AG2514TF) to compare performances in water yield and quality for the same pumping costs. The results show that NF allows higher yield, while respecting the Tunisian standard of water reuse (COD < 90 mg L-1). Above 9 bar, the TDS rejection reaches 60% and the hardness is lower than the factory constraint (100 mg L-1 CaCOA allowing the reuse of the water in the process.

Ref HAL: hal-00439698_v1
Ref Arxiv: 0911.1730
Ref. & Cit.: NASA ADS
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A variational theory is developed to study electrolyte solutions, composed of interacting point-like ions in a solvent, in the presence of dielectric discontinuities and charges at the boundaries. Three important and non-linear electrostatic effects induced by these interfaces are taken into account: surface charge induced electrostatic field, solvation energies due to the ionic cloud, and image charge repulsion. Our variational equations thus go beyond the mean-field theory. The influence of salt concentration, ion valency, dielectric jumps, and surface charge is studied in two geometries. i) A single neutral air-water interface with an asymmetric electrolyte. A charge separation and thus an electrostatic field gets established due to the different image charge repulsions for coions and counterions. Both charge distributions and surface tension are computed and compared to previous approximate calculations. For symmetric electrolyte solutions close to a charged surface, two zones are characterized. In the first one, with size proportional to the logarithm of the coupling parameter, strong image forces impose a total ion exclusion, while in the second zone the mean-field approach applies. ii) A symmetric electrolyte confined between two dielectric interfaces as a simple model of ion rejection from nanopores. The competition between image charge repulsion and attraction of counterions by the membrane charge is studied. For small surface charge, the counterion partition coefficient decreases with increasing pore size up to a critical pore size, contrary to neutral membranes. For larger pore sizes, the whole system behaves like a neutral pore. The prediction of the variational method is also compared with MC simulations and a good agreement is observed.

Ref HAL: hal-00170107_v1
DOI: 10.1016/j.memsci.2007.07.033
WoS: 000256599300002
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9 Citations
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By extrapolation of the extensive use of cyclodextrin (CD)-modified materials in chromatography techniques, we study CD-containing membranes as contactors having facilitated transport properties in liquid/liquid extraction. Our main interest lies in the understanding and modelling of the mass transport mechanism for the development of pertraction applications using these membranes. The sorption and diffusion processes of xylenes as model molecules were studied through sorption experiments in membranes containing alpha-CD. The presence of highly pronounced induction times on sorption curves makes it impossible to use standard models, like the solution-diffusion one, to describe the experimental data. A generalized dual mode model has therefore been developed to account for three distinct regimes of strong facilitated transport membranes: (i) one controlled by diffusion within a membrane, (ii) one controlled by a kinetic retardation of solute entry into and out of a membrane, and (iii) one controlled by the kinetics of complexation formation. The permeant species are divided into two populations: one diffusing in the membrane and one forming immobile inclusion complexes with fixed CD sites. The model fits, which agree well with the experimental data using a limited number of adjustable parameters, indicate that the kinetics of interfacial transfer depends on the CD content.

Ref HAL: hal-00316382_v1
Ref Arxiv: 0809.0456
Ref. & Cit.: NASA ADS
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We develop further a statistical model coupling denaturation and chain conformations in DNA (Palmeri J, Manghi M and Destainville N 2007 Phys. Rev. Lett. 99 088103). Our Discrete Helical Wormlike Chain model takes explicitly into account the three elastic degrees of freedom, namely stretching, bending and torsion of the polymer. By integrating out these external variables, the conformational entropy contributes to bubble nucleation (opening of base-pairs), which sheds light on the DNA melting mechanism. Because the values of monomer length, bending and torsional moduli differ significantly in dsDNA and ssDNA, these effects are important. Moreover, we explore in this context the role of an additional loop entropy and analyze finite-size effects in an experimental context where polydA-polydT is clamped by two G-C strands, as well as for free polymers.

Commentaires: 18 pages, 30 figures

Ref HAL: hal-00123812_v1
PMID 17930986
Ref Arxiv: cond-mat/0612588
DOI: 10.1103/PhysRevLett.99.088103
WoS: 000248984900055
Ref. & Cit.: NASA ADS
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41 Citations
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A statistical model of homopolymer DNA, coupling internal base pair states (unbroken or broken) and external thermal chain fluctuations, is exactly solved using transfer kernel techniques. The dependence on temperature and DNA length of the fraction of denaturation bubbles and their correlation length is deduced. The thermal denaturation transition emerges naturally when the chain fluctuations are integrated out and is driven by the difference in bending (entropy dominated) free energy between broken and unbroken segments. Conformational properties of DNA, such as persistence length and mean-square-radius, are also explicitly calculated, leading, e.g., to a coherent explanation for the experimentally observed thermal viscosity transition.

Ref HAL: hal-00173154_v1
PMID 18351882
Ref Arxiv: 0709.2843
DOI: 10.1103/PhysRevE.77.011913
WoS: 000252861400076
Ref. & Cit.: NASA ADS
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35 Citations
Résumé:

Statistical DNA models available in the literature are often effective models where the base-pair state only (unbroken or broken) is considered. Because of a decrease by a factor of 30 of the effective bending rigidity of a sequence of broken bonds, or bubble, compared to the double stranded state, the inclusion of the molecular conformational degrees of freedom in a more general mesoscopic model is needed. In this paper we do so by presenting a 1D Ising model, which describes the internal base pair states, coupled to a discrete worm like chain model describing the chain configurations [J. Palmeri, M. Manghi, and N. Destainville, Phys. Rev. Lett. 99, 088103 (2007)]. This coupled model is exactly solved using a transfer matrix technique that presents an analogy with the path integral treatment of a quantum two-state diatomic molecule. When the chain fluctuations are integrated out, the denaturation transition temperature and width emerge naturally as an explicit function of the model parameters of a well defined Hamiltonian, revealing that the transition is driven by the difference in bending (entropy dominated) free energy between bubble and double-stranded segments. The calculated melting curve (fraction of open base pairs) is in good agreement with the experimental melting profile of polydA-polydT. The predicted variation of the mean-square-radius as a function of temperature leads to a coherent novel explanation for the experimentally observed thermal viscosity transition. Finally, the influence of the DNA strand length is studied in detail, underlining the importance of finite size effects, even for DNA made of several thousand base pairs.

Commentaires: 28 pages pdf, 9 figures