Water transport study across commercial ion exchange membranes in the vanadium redox flow battery

The water transfer behaviour of Selemion CMV, AMV and DMV membranes (Asahi Glass, Japan) has been studied in the vanadium redox cell, as was the water transfer across Nafion 117 membrane (E.I. Du Pont, USA). The earlier water transport studies of a variety of commercial ion exchange membranes and non-ionic separators in the vanadium redox cell have shown that the net water transport through anion exchange membranes and non-ionic separators in the vanadium redox cell is from the positive half cell (+ve) to the negative half cell (−ve), while for cation exchange membranes the net water transport is in the opposite direction. In the present study, it was found that a significant amount of water is transferred across cation exchange membranes from the −ve vanadium half cell electrolyte to the +ve vanadium half cell electrolyte by the hydration shells of V²⁺ and V³⁺ ions which carry a large amount of water and can easily permeate through cation exchange membranes due to their relatively high charge numbers. The net amount of water of hydration which is transferred across anion exchange membranes from the −ve half cell electrolyte, however, is almost equal to the net amount of water of hydration which is transferred from the +ve half cell electrolyte. Thus, the net amount of water which is transferred across anion exchange membranes is in the same direction as the osmotic water transfer.     

Simulation of Polymer Reactors Using the Compartment Modeling Approach

A compartment modeling approach based on computational fluid dynamics (CFD) simulations is applied to a simplified static mixer geometry. Compartments are derived from velocity fields obtained from cold CFD simulations. This methodology is based on the definition of periodic flow zones (PFZ) derived from the recurrent flow profile within the static mixer. In general, PFZ can be characterized by two different compartments: flow zones with hydrodynamic behavior of a tubular reactor and dead zones exhibiting a more continuous stirred tank reactor‐like characteristic. In CFD studies the influence of changing fluid properties, for example viscosity, on flow profile due to polymerization progress is considered. In the deterministic compartment model, the continuous flow profile within the static mixer is transformed to basic reactor models interconnected via an exchange stream. To reduce model complexity and the number of model parameters, constant volumes of compartments are assumed. Changes in hydrodynamics are considered by a variable exchange flow rate as a function of Re manipulating residence time in compartments. Simulation studies show the influence of decreasing exchange flow rates with polymerization progress, as Re decreases, resulting in a greater increase of viscosity in dead zones. The reactor performance is qualitatively represented by the simulation results.     

Dynamics of hyaluronan aqueous solutions as assessed by fast field cycling NMR relaxometry

Fast field cycling (FFC) NMR relaxometry has been used to study the conformational properties of aqueous solutions of hyaluronan (HYA) at three concentrations in the range 10 to 25 mg mL^–1. Results revealed that, irrespective of the solution concentration, three different hydration layers surround hyaluronan. The inner layer consists of water molecules strongly retained in the proximity of the HYA surface. Because of their strong interactions with HYA, water molecules in this inner hydration layer are subject to very slow dynamics and have the largest correlation times. The other two hydration layers are made of water molecules which are located progressively further from the HYA surface. As a result, decreasing correlation times caused by faster molecular motion were measured. The NMRD profiles obtained by FFC-NMR relaxometry also showed peaks attributable to ¹H–¹⁴N quadrupole interactions. Changes in intensity and position of the quadrupolar peaks in the NMRD profiles suggested that with increasing concentration the amido group is progressively involved in the formation of weak and transient intramolecular water bridging adjacent hyaluronan chains. In this work, FFC-NMR was used for the first time to obtain deeper insight into HYA–water interactions and proved itself a powerful and promising tool in hyaluronan chemistry.     

Hydration behavior of heart muscle studies by nuclear magnetic relaxation: Deuterium exchange of water protons in the myocardium

Proton transverse relaxation, deuterium and oxygen-17 NMR measurements on functional animal heart muscle were employed to study the distribution and exchange of water protons in the heart. Our nonlinear regression analysis of such data showed the presence of three proton transverse relaxation components that are likely to correspond, respectively, to two major types of water compartments in the heart muscle and the heart muscle matrix. A deuterium exchange study was undertaken to obtain additional information concerning the chemical exchange of water protons/deuterium within these two water compartments, and the effects of proton intermolecular dipolar interactions on the transverse relaxation of water protons. Our results are likely to influence the analysis and interpretation of MRI data for myocardium since it provides details of the microscopic water distribution in the myocardium which is important to the heart function.     

Electrodialysis of uranium(VI) through cation exchange membranes and modeling of electrodialysis processes

The transport of ionic species through ion exchange membranes found several applications for water effluents purification and metal ion separation. To enhance the transport performance, the effect of electric fields was suggested in this work. The transport of U(VI) species in nitric acid solutions across cation exchange membranes was investigated. Different parameters affecting the transport of U(VI) were studied. These parameters include: nitric acid concentration in the feed solution, stripping solution concentration and applied electric field. From the results obtained, the cationic flux of U(VI) was 6.5^.10^–8 geq^.cm^–2.s^–1 at the optimal conditions of 10^–3M HNO₃ in the feed solution, 0.5M Na₂CO₃ in the stripping solution and 30 V. The modeling of the electrodialysis process was also made. The model correlates the mass transfer as a function of current density and voltage as variables and takes into account the electro-osmotic effect. The model is applied to the experimental data.     

A study of the proton exchange in tissue water by spin relaxation in the rotating frame

The exchange rate of the water protons in mouse tissues was determined for the first time. The process was studied by proton spin relaxation in the rotating frame. The exchange correlation time was found to be ≈5 × 10^?6 sec. The actual residence time of a water proton on one water molecule in tissue was estimated to be ≈ 10^?6 sec. It is shown that because of the fast exchange the estimate (≈10%) of the amount of ordered water is too low.     

Viscoelastic properties of Nafion at elevated temperature and humidity

Tensile stress–strain and stress relaxation properties of 1100 equivalent weight Nafion have been measured from 23 to 120 °C at 0–100% relative humidity. At room temperature, the elastic modulus of Nafion decreases with water activity. At 90 °C, the elastic modulus goes through a maximum at a water activity of ～ 0.3. At temperatures ≥90 °C, hydrated membranes are stiffer than dry membranes. Stress‐relaxation was found to have two very different rates depending on strain, temperature, and water content. At high temperature, low water activity, and small strain, the stress relaxation displays a maximum relaxation time with stress approaching zero after 10³–10⁴ s. Water absorption slows down stress‐relaxation rates. At high water activity, the maximum stress relaxation time was >10⁵ s at all temperatures. No maximum relaxation time was seen at T ≤ 50 °C. Increasing the applied strain also resulted in no observed upper limit to the stress relaxation time. The results suggest that temperature, absorbed water, and imposed strain alter the microstructure of Nafion inducing ordering transitions; ordered microstructure increases the elastic modulus and results in a stress relaxation time of >10⁵ s. Loss of microphase order reduces the elastic modulus and results in a maximum stress relaxation time of 10³–10⁴ s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 11–24, 2009.     

A rapid method for the determination of radionuclides in reactor coolant by ion exchange membranes

This paper deals with a rapid method to determine radionuclides in reactor coolant by anion, cation, and anion-cation exchange membranes. A high pressure filtration device was established to simulate the THOR cooling water sampling system by means of several membranes mentioned above. The experimental results indicate that the adsorption efficiency of each membrane for several radionuclides is /1/ >95% with cation exchange membrane for Zn, Co, Na, Mn, Cu, Cs, Ba, La, W etc., /2/ >98% with anion exchange membrane for I, and /3/ <98% with anion-cation exchange membranes for Fe and Cr. The results are obtained using cooling water of Tsing Hua Open-Pool Reactor and the following radionuclides were identified:^99mTc,¹⁴⁰Ba,¹⁴⁰La,⁵¹Cr,¹³¹I,⁵⁸Co,⁶⁰Co,⁵⁴Mn,⁴⁶Sc,⁵⁹Fe,²⁴Na, etc.     

Recent developments in the characterization of water interacting with proteins by 17O NMR

Transverse and longitudinal ¹⁷O-water relaxation rates were detected in different samples of BSA solutions after one-quantum and triple-quantum-filtered NMR sequences. Another contribution other than quadrupolar relaxation was found for transverse relaxation, which did not change significantly with the concentration and hence could not correspond to agglomeration of proteins. This was interpreted as chemical exchange between different types of ¹⁷O-water in fast motion; probably free water and water weakly bound to the proteins. At lower BSA concentrations, two peaks were detected for water; this was in agreement with this hypothesis. The interactions between BSA and lactic acid were also studied. It was shown that at a sufficient concentration of lactic acid, the number of strongly bound water molecules detected diminishes. On the other hand, the weakly bound water properties do not change significantly.     

Investigating the New Interaction Model between Cu(II) and PVA by the Proton Relaxation Method

An aqueous PVA-Cu²⁺ solution at pH = 3 is in the hydrated form and becomes green at pH ? 6 with a decrease in viscosity. The structure of the copper ion is suggested to be that of a polynuclear complex at pH > 6. For the green solution the polynuclear chains of the copper complex are believed to be surrounded by the PVA chains with the hydrophobic backbones facing toward the inside and the hydrophilic OH groups oriented toward the outside facing the bulk water. The proton spin-lattice relaxation rate 1/T_1p and the spin-spin relaxation rate 1/T₂ of CH and CH₂ in PVA and H₂O for aqueous PVA-Cu²⁺ solutions at pH = 3, can be explained by the two site exchange model in the region of the fast exchange limit. The dipolar correlation time τ_c is dominated by the reorientational process with a dipolar correlation time of 2.11 × 10^?11 s. When the pH rises from pH=3 to pH=12.5, the variation of 1/T₁p and 1/T₂p of CH and CH₂ in PVA with Cu²⁺ ion concentration in aqueous PVA-Cu²⁺ solution at pH=12.5 can be explained in terms of the relaxation by an inclusive model of the polynuclear copper complex and PVA. Furthermore, the frequency (or field) dependence of 1/T₁p, 1/T₂p of CH in PVA for aqueous PVA-Cu²⁺ solution at pH = 12.5 suggests that the dipolar relaxation is dominated by the electron-spin relaxation with the electron spin relaxation time T_1e = 1 ? 2 × 10^?10 s. The invariance of 1/T₁p and 1/T₂p of H₂O with the variation of the Cu²⁺ ion concentration in aqueous PVA-Cu²⁺ solution at pH = 12.5 supports the hypothesis that the water is not directly bound to the Cu²⁺ ion.     

Water Relaxation Measurements on Semiquinones of Various Flavoproteins

The water relaxation rates of several flavoproteins in the semiquinone state have been investigated by the spin echo technique. The results indicate a rather unspecific interaction between water and the protein-bound flavosemiquinones. An average interaction distance of 0.3-0.5 nm has been estimated. From the temperature dependence of the rate constants the free energy of activation for proton exchange is calculated to be about 17 kJ/mol. The rate of proton exchange is around 10¹¹ s?¹ for the flavosemiquinones investigated are accessible to water regardless of their ionic state. The large difference in relaxation rates of water protons between D - and L - amino-acid oxidases is noticeable. Oxynitrilase exhibits the highest whereas Azotobacter vinelandii flavodoxin shows the lowest water relaxation rate of the flavoproteins studied. The results are discussed in relation to the visible-light absorption properties of the flavoproteins.     

Electro-electrodialysis of hydriodic acid using the cation exchange membrane cross-linked by accelerated electron radiation

Electro-electrodialysis (EED) of hydriodic acid with HI molality of ca. 9.5 mol/kg was examined in the presence of iodine using a commercial cation exchange membrane (CMB) as a separator. For the increase of the selectivity of proton permeation, the membrane was cross-linked by accelerated electron radiation. The membrane properties (area resistance, ion exchange capacity (IEC), water content) of the cross-linked membranes were measured. The area resistance in 2 mol/dm³ KCl solution of the cross-linked membranes decreased as compared with that of the non-cross-linked membrane (original of CMB membrane). The IEC and water content of cross-linked membranes at each dose rate had almost the same value as that of non-cross-linked membrane. Electro-electrodialysis of hydriodic acid with HI molality of ca. 9.5 mol/kg was examined at 75 °C with 9.6 A/dm². The cross-linked cation exchange membrane by accelerated electron radiation had higher selectivity of the proton permeation by cross-linking structure of polymer than that of the non-cross-linked membrane.     

Gd‐DTPA‐Dopamine‐Bisphytanyl Amphiphile: Synthesis,Characterisation and Relaxation Parameters of the Nanoassemblies and Their Potential as MRI Contrast Agents

Here, a new amphiphilic magnetic resonance imaging (MRI) contrast agent, a Gd^III‐chelated diethylenetriaminepentaacetic acid conjugated to two branched alkyl chains via a dopamine spacer, Gd‐DTPA‐dopamine‐bisphytanyl (Gd‐DTPA‐Dop‐Phy), which is readily capable of self‐assembling into liposomal nanoassemblies upon dispersion in an aqueous solution, is reported. In vitro relaxivities of the dispersions were found to be much higher than Magnevist, a commercially available contrast agent, at 0.47 T but comparable at 9.40 T. Analysis of variable temperature ¹⁷O NMR transverse relaxation measurements revealed the water exchange of the nanoassemblies to be faster than that previously reported for paramagnetic liposomes. Molecular reorientation dynamics were probed by ¹H NMRD profiles using a classical inner and outer sphere relaxation model and a Lipari–Szabo “model‐free” approach. High payloads of Gd^III ions in the liposomal nanoassemblies made solely from the Gd‐DTPA‐Dop‐Phy amphiphiles, in combination with slow molecular reorientation and fast water exchange makes this novel amphiphile a suitable candidate to be investigated as an advanced MRI contrast agent.     

Interactions of La(III) with anions in aqueous solutions. A139La NMR study

The interactions of the La(III) cations with three anions (X), nitrate, chloride and perchlorate, in aqueous solutions in the pH range 4.0–6.5, were studied by¹³⁹La NMR spectroscopy. A single model, involving the formation of the contact ion-pair (inner-sphere complex) (LaX)²⁺ was successfully and quantitatively applied to the chemical shift and the transverse relaxation rate data. Both measurements gave values for the thermodynamic equilibrium constants of formation of (LaX)²⁺ (K _th ) in good agreement (average K _th =0.45±0.05; 0.15±0.09; 0.03±0.01, respectively for nitrate, chloride and perchlorate). The complexes are characterized by chemical shifts of –25, 22 and –3.1 ppm and by transverse relaxation rates of 11.2, 5 and 1.65 kHz respectively for nitrate, chloride and perchlorate. The¹³⁹La quadrupolar relaxation rate is not controlled by the reorientational correlation time. This finding is discussed, and it is suggested that the very fast exchange of water molecules in the first coordination sphere of La(III) is responsible for the time fluctuation of the electric field gradient at the¹³⁹La nucleus site.     

Donnan dialysis of copper, gold and silver cyanides with various anion exchange membranes

Donnan dialysis is an ion exchange membrane process that can be used for the purification and concentration of diluted solutions. In this work, the behaviour of gold, silver and copper in cyanide medium is examined. Flux of cyanide complexes and corresponding free cyanide are determined using five commercial anion exchanger membranes (AMV, ACS, RAI 5035, ADP and ADS). The results show that the rate transfer depends upon the nature of the anion exchanger membrane. It is observed that the species number in the feed solution influences the transfer selectivity of metal ion complex against free cyanide Thus, gold which forms only one stable species with cyanides is transferred faster through an ACS membrane than copper which forms three species. However, this result is not verified when an ADS membrane is used. A model of the complex transfer through anion exchange membranes based on Donnan dialysis is proposed. A three compartment Donnan dialysis is performed to improve the separation between the studied metals. Decyanidation is also examined and separation factors are calculated. It is shown that Donnan dialysis can be an efficient technique for the separation of cyanides complexes of copper, gold and silver when parameters such as anion exchange membrane and the number of compartments are optimised. An advantage of this technique is also the possibility of recycling all reactants with a good impact on the environment.     

Electro-adsorption of polyethyleneimine on the anion exchange membrane: Application to the nitrate removal from loaded solutions

Anion exchange membrane has been modified by fixation of polyethyleneimine. The modification has been carried out aiming to achieve a separation of anions according to their hydration radii and their sizes. The performances of the modified membranes were compared with the unmodified one by applying Donnan dialysis of nitrate ion using Cl⁻ in the strip compartment. The transfer of nitrate ions in the presence of chloride was enhanced by using immersion modified membrane. The presence of a thin layer of PEI on the strip side of the membrane improves Cl⁻ transference, by creating a chemical potential difference which increases the transfer.     

Concentration and fractionation by isoelectric trapping in a micropreparative-scale multicompartmental electrolyzer having orthogonal pH gradients. Part 1

A multicompartmental electrolyzer called ConFrac has been developed and tested for micropreparative-scale isoelectric trapping separations. ConFrac contains n separate, minimalistic isoelectric trapping core units, each with a separate anode compartment, anodic flow-through compartment, collection compartment, cathodic flow-through compartment and a shared cathode compartment. The collection compartments are all isolated from each other and have volumes of 100 μL each. The liquid held in the collection compartments is stagnant. The respective anodic and cathodic flow-through compartments are hydraulically serially connected to each other by flexible, minimum-length, narrow internal diameter tubes. The respective feed solutions whose volumes are larger and variable are recirculated through the serially connected flow-through compartments. Poly(vinyl alcohol)-based buffering membranes are placed between the anode compartments, anodic flow-through compartments, collection compartments, cathodic flow-through compartments and cathode compartment. The membranes establish two orthogonal pH gradients in ConFrac. The primary pH gradient is parallel with the direction of the recirculating flows and orthogonal to that of the electric field. The secondary pH gradient is parallel with the direction of the electric field and orthogonal to that of the recirculating flows. Since the recirculating liquids are kept in thermostated reservoirs and the residence times in the flow-through compartments are shorter than 2 s, ConFrac can tolerate power loads as high as 2 W without overheating the solutions. The operation and performance of ConFrac has been quantitatively characterized: four 25 μM ampholytic components were isolated from 5 mL of feed solution in 20 min and their concentration increased approximately 50-fold.     

Water Dynamics in Nafion Fuel Cell Membranes: the Effects of Confinement and Structural Changes on the Hydrogen Bond Network

The complex environments experienced by water molecules in the hydrophilic channels of Nafion membranes are studied by ultrafast infrared pump-probe spectroscopy. A wavelength dependent study of the vibrational lifetime of the O-D stretch of dilute HOD in H(2)O confined in Nafion membranes provides evidence of two distinct ensembles of water molecules. While only two ensembles are present at each level of membrane hydration studied, the characteristics of the two ensembles change as the water content of the membrane changes. Time dependent anisotropy measurements show that the orientational motions of water molecules in Nafion membranes are significantly slower than in bulk water and that lower hydration levels result in slower orientational relaxation. Initial wavelength dependent results for the anisotropy show no clear variation in the time scale for orientational motion across a broad range of frequencies. The anisotropy decay is analyzed using a model based on restricted orientational diffusion within a hydrogen bond configuration followed by total reorientation through jump diffusion.     

Quantitative MRI analysis of structural changes in tomato tissues resulting from dehydration

A quantitative magnetic resonance imaging (MRI) analysis at 1.5T of the effects of different dehydration regimes on transverse relaxation parameters measured in tomato tissue is presented. Multi-exponential T₂ maps have been estimated for the first time, providing access to spatialized microstructural information at voxel scale. The objective was to provide a better understanding of the changes in the multi-exponential transverse relaxation parameters induced by dehydration in tomato tissues and to unravel the effects of microstructure and composition on relaxation parameters. The results led to the hypothesis that the multi-exponential relaxation signal reflects cell compartmentation and tissue heterogeneity, even at the voxel scale. Multi-exponential relaxation times provided information about water loss from specific cell compartments and seem to indicate that the dehydration process mainly affects large cells. By contrast, total signal intensity showed no sensitivity to variations in water content in the range investigated in the present study (between 95% [fresh tissue] and 90% [after dehydration]). The variation in relaxation times resulting from water loss was due to both changes in solute concentration and compartment size. The comparative analysis of the two contrasted tissues in terms of microporosity demonstrated that magnetic susceptibility effects, caused by the presence of air in the placenta tissue, significantly impact the effective relaxation and might be the dominant effect in the variations observed in relaxation times in this tissue.