The Mechanism of a Selective Permeation of Ions through “Solvent Polymeric Membranes”

Abstract

The mechanism of diffusion of uranyl nitrate in “solvent polymeric membranes” was investigated. It is suggested that a “carrier” transport mechanism is responsible for the selective permeation of ions or ion pairs through such membranes. The fluidity of the membranes was investigated by proton magnetic resonance and by the “fluorescent probe” technique. Radioactive labeling was used in order to determine the self-diffusion coefficient of dicresylbutylphosphate (DCBP) which serves both as plasticizer and as complexing agent in such membranes. Comparison of its value (～10^?7 cm²/sec) with the limiting value of the diffusion coefficient of uranyl nitrate in such membranes (3.3 × 10^?8 cm²/sec) indicates that the latter diffuses as a (DCBP)₂UO₂(NO₃)₂ complex. It is also suggested that the study of the “solvent polymeric membranes” may help to understand certain properties of biological membranes.     

Separation of Carboxylic Acids from Carboxylates by Diffusion Dialysis

Abstract

Acetic acid/sodium acetate and propionic acid/sodium propionate were separated by the diffusion dialysis technique using Neosepta AFN‐7 and Selemion DSV membranes. Accounting for molarities of carboxylic acids and salts in broths produced by the pH controlled bacterial fermentation (pH 4–6), the experiments were carried out with carboxylates in excess of acids. The sorption equilibria established for acetic acid, propionic acid, and the sodium salts of both acids (single solute experiments) revealed a high sorption of acids in both membranes and the rejection of carboxylates. The partition coefficients were found to be from unity up to 2 for the acids and 0.04–0.05 for the salts. Reflecting a high sorption, the fluxes for the acids amounted from 1.5 to 2.0 mol · m^?2 · h^?1 and only 0.07–0.08 mol · m^?2 · h^?1 for the salts (one molar solutions). The separation factors computed upon the experiments performed with the ternary solutions were found between 20 to 37 for the Neosepta AFN‐7 membrane and about 29 for the Selemion DSV membrane. Accounting additionally, for the results of the separation of lactic acid from sodium lactate reported in our earlier paper the results prove the diffusion dialysis to be applicable to the separation of mean strength and weak carboxylic acids from their salts.     

Polymeric alloys of polyphosponates and acetyl cellulose. I. Sorption and diffusion of benzene and cyclohexane

The solubility of benzene in the polymeric alloys (P/A) consisting of polyphosphonates (PPN) and acetyl cellulose (AC) is nearly two orders of magnitude larger than that of cyclohexane. The preferential absorption of benzene by P/A membranes is also maintained upon its dilution with cyclohexane, though the solubility of the latter in the P/A membranes is affected by their swelling with benzene. Absolute values of solubilities increase exponentially with increase in the weight fraction of PPN in P/A membranes. They are also affected by the thermal and solvent “history” of a membrane. For the sorption of benzene by a P/A-50 membrane The diffusion coefficients of benzene in the solvent-swollen membranes are strongly concentration dependent and increase exponentially up to ～10^?6 cm²/sec with the increase in the volume fraction of benzene. Values of D₀ are of the order of 10^?11 to 10^?10 cm²/sec. Sorption experiments indicate a pronounced time dependence of the diffusion coefficients. Self-diffusion experiments conducted with ¹⁴C-labeled benzene revealed that values of D* derived from the steady-state permeation measurements are in certain membranes much larger than those derived from the “time-lag.” It was observed that the discrepancies between the two sets of values depend strongly upon the thermal “history” of the membranes and vanish when the membranes are swollen to a high degree at elevated temperatures. The above phenomenon is discussed in terms of differences in the membrane structure; a model is proposed. The apparent energy of activation of diffusion of benzene at 10–40°C in the swollen P/A-50 membrane E_B^D 14.4 kcal/mole was derived from the temperature dependence of the self-diffusion coefficients. For the same temperature range at C_(B) → 0, E_B = 8.3 kcal/mole was derived from the final slopes of the desorption curves. The small difference between the energies of activation in a swollen and in an unswollen system is due to the fact that at room temperature it remains below T_g even upon extensive swelling with benzene.     

Characterization and determination of swelling and diffusion characteristics of poly(n‐vinyl‐2‐pyrrolidone) hydrogels in water

Hydrogels in the form of rods with varying crosslink densities and three‐dimensional network structures were prepared from Poly(N‐vinyl‐2‐pyrrolidone) (PVP)/water and PVP/water/persulfate systems by irradiation with γ rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non‐Fickian type diffusion and diffusion coefficients vary from 6.56 × 10⁻⁷ to 2.51 × 10⁻⁷cm²min⁻¹ for PVP and 6.09 × 10⁻⁷ to 2.14 × 10⁻⁷ cm²min⁻¹ for PVP/persulfate hydrogel systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 994–1000, 2000     

The transport properties of oxygen in aqueous borate solutions

The solubility and diffusivity of oxygen in borate buffer solutions were studied on a Pt μ electrode under diffusion-controlled conditions. The solubility of oxygen in diluted borate solution is unusually high (4.2 × 10⁻³ M l⁻¹), whereas its diffusion coefficient is lower (5 × 10⁻⁶ cm² s⁻¹) than in other aqueous solutions The decrease in oxygen solubility at higher ionic strengths is due to the salting-out effect. The results are consistent with the formation of “oxygen-borate” complex whereby the stability of BO₃ containing polymeric anions is enhanced.     

Phenol transport in cellulose acetate membranes

Past detailed studies of solute transport through reverse-osmosis membranes have been conducted only with simple salts. The present work with phenol was undertaken largely because of the practical observation that the transport of low molecular weight organics is much more rapid than that of the salts. Studies of phenol sorption from dilute aqueous solution indicate that the diffusion coefficient for phenol in water-saturated 39.8 wt.-% acetyl cellulose acetate is 9.6 × 10^-10 cm.²/sec., and the equilibrium distribution coefficient between the acetate phase and water is 42. Thus, the diffusion coefficient is quite close to that measured for sodium chloride, and the higher permeability of the membranes to phenol can be attributed entirely to their greater sorption of this solute. In direct osmosis experiments performed with significant water flow a measurable interaction or positive coupling between water and phenol flows has been observed. Further evidence of flow coupling is derived from reverse osmosis experiments in which significant negative solute rejection is observed; i.e., the permeate is enriched in phenol by as much as 20%. It is shown that a solution-diffusion transport model is not adequate to rationalize the results, and a more complex transport model is apparently required.     

Swelling kinetics of linseed oil‐based nanocomposites

The solvent‐resistance properties of the montmorillonite‐filled conjugated linseed oil‐based nanocomposites are studied in tetrahydrofuran through equilibrium swelling method at different temperatures. The values of “n” in solvent transport equation are found to be below “0.5,” showing the non‐Fickian diffusion in the polymer. The dependence of the diffusion coefficient on the composition, percentage of clay, and temperature has been studied for nanocomposite samples. The diffusion coefficient increases with an increase in the clay contents and temperature. The crosslink density of the nanocomposites ranges from 101.07 to 237.46 × 10⁶ mol/cm³. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication and performance of a polyethersulfone nanofiltration membrane impregnated with a mesoporous silica–poly(1‐VInylpyrrolidone) nanocomposite

Fouling is a serious problem in the membrane formation process. Adding hydrophilic polymers or inorganic particles into the membrane is an effective way for improving the antifouling performance. However, most of the water‐soluble polymeric additives leach out during the phase inversion process, and the inorganic particles are prone to agglomerate in the membrane, which decreases the antifouling property of the membrane. In this study, poly(1‐vinylpyrrolidone) (PVP) was grafted onto mesoporous silica (MS) nanoparticle surface, and polyethersulfone (PES)/MS–PVP nanocomposite membranes were fabricated by the phase inversion method. MS–PVP dispersed well on the membrane surface, and the hydrophilicity of the PES/MS–PVP membranes increased with increasing content of MS–PVP. PES/MS–PVP membranes exhibited higher water flux than that of the bare PES membrane without any loss in NaCl rejection, and water flux of 25 L/m²h could be achieved by the membrane containing 3% of MS–PVP, which is almost 1.5 times as high as that of bare PES membrane at 0.6 MPa. The protein adsorption onto the membrane surface declined significantly from 49 to 25 mg/cm² when the MS–PVP loading increased from 0% to 3%. POLYM. COMPOS., 38:908–917, 2017. © 2015 Society of Plastics Engineers     

Novel ion-containing reverse osmosis membranes. II. Reverse osmosis properties

The reverse osmosis properties of ion-containing membranes prepared by ⁶⁰Co mutual irradiation grafting of 2-vinylpyridine to poly(3,3-bis(chloromethyl)oxetane) (polyoxetane, Penton) followed by quaternization with methyl bromide are presented. In general, the volumetric fluxes varied linearly with pressures up to 55 atm. Katchalsky's treatment of membrane permeability was used to analyze the data. Membrane constants and diffusion coefficients of water and sodium chloride were determined with membranes containing different volume fractions of water. The diffusion coefficients of water in the membranes were of the same order of magnitude as the self-diffusion coefficient of water (～3 × 10^?5 cm²/s). The diffusion coefficients of sodium chloride in the membrane were of the order of 10^?7 cm²/s. The diffusion coefficients increased with hydration, and the salt rejections were markedly affected by the external salt concentrations. The apparent energies of activation for the volumetric flux were calculated in distilled water and in 0.5% sodium chloride solution.     

Preparation and properties of bisphenol A‐based sulfonated poly(arylene ether sulfone) proton exchange membranes for direct methanol fuel cell

Novel bisphenol A‐based sulfonated poly(arylene ether sulfone) (bi A‐SPAES) copolymers were successfully synthesized via direct copolymerization of disodium 3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone, 4,4′‐dichlorodiphenylsulfone, and bisphenol A. The copolymer structure was confirmed by Fourier transform infrared spectra and ¹H NMR analysis. The series of sulfonated copolymers based membranes were prepared and evaluated for proton exchange membranes (PEM). The membranes showed good thermal stability and mechanical property. Transmission electron microscopy was used to obtain the microstructures of the synthesized polymers. The membranes exhibit increased water uptake from 8% to 66%, ion exchange capacities from 0.41 to 2.18 meq/g and proton conductivities (25°C) from 0.012 to 0.102 S/cm with the degree of sulfonation increasing. The proton conductivities of bi A‐SPAES‐6 membrane (0.10–0.15 S/cm) with high‐sulfonated degree are higher than that of Nafion 117 membrane (0.095–0.117 S/cm) at all temperatures (20–100°C). Especially, the methanol diffusion coefficients of membranes (1.7 × 10^?8 cm²/s–8.5 × 10^?7 cm²/s) are much lower than that of Nafion 117 membrane (2.1 × 10^?6 cm²/s). The new synthesized copolymer was therefore proposed as a candidate of material for PEM in direct methanol fuel cell. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Behaviour of composites used in the confinement of nuclear wastes. 3. Diffusion of ions through epoxide networks

The diffusion of cesium and chloride ions through epoxide membranes was studied under a variety of conditions including self-diffusion, the presence of other salts in the aqueous solution, an excess of either reagent used in the manufacture of the membrane, the addition of various fillers in the epoxide network and two temperatures. At 23°C, the diffusion coefficient D was (2–6) × 10-¹³cm²s^?1 for most systems, except when the epoxide was prepared with an excess of the dioxirane component or when untreated glass beads were added to the network. In the latter instance D increased and most notably with glass beads. On the contrary, addition of sand to the epoxide resulted in a more effective barrier against diffusion as shown by a decrease in D. It is concluded that most of these materials should be suitable for the confinement of low and medium activity nuclear wastes.     

The interaction of hydrogen sulfide with lead- and barium–cadmium–zinc-stabilized poly(vinyl chloride)

Poly(vinyl chloride) polymers stabilized with tribasic lead sulfate discolor upon exposure to hydrogen sulfide gas as a result of lead sulfide formation. The discoloration occurs for samples in both cord and sheet forms and is shown to be a function of total H₂S exposure, reaching a limiting value that is determined by the amount of lead stabilizer used in the polymer formulation. The permeation and diffusion constants for H₂S through PVC stabilized with tribasic lead sulfate and with a liquid Ba–Cd–Zn formulation are found to be P_Pb = (6.0 ± 0.2) × 10^?9, P_BaCdZn = (5.2 ± 0.2) × 10^?9 (both in cm³ gas?cm film/cm² area?sec?cm Hg), D_Pb = (1.3 ± 0.2) × 10^?7 cm²/sec, and D_BaCdZn = (6.4 ± 0.6) × 10^?8 cm²/sec, all measured at 21°C. The stabilizing efficiencies of the formulations were assessed by HCl evolution measurements, which show that exposure to H₂S decreases the initial polymer stability for both Pb-stabilized and Ba–Ca–Zn-stabilized formulations. Protection of stabilized PVC formulations from diffusing hydrogen sulfide is thus advisable for long-term stability as well as for color integrity.     

The dependence of morphology of solid polymer electrolyte membranes on transient salt type: effect of cation type

The structures of poly(N‐vinyl pyrrolidone) (PVP) and poly(ether sulfone) composite membranes were investigated with transient salt addition. The effects of type and concentration of AgNO₃ and Cu(NO₃)₂ on membrane morphology were evaluated through attenuated total reflection Fourier transform infrared (ATR‐FTIR) spectroscopy, differential scanning calorimetry (DSC) and atomic force microscopy. Complex formation between carbonyl groups (on PVP chains) and Cu²⁺ or Ag⁺ decreases the strength of the carbonyl bond as evidenced through ATR‐FTIR spectroscopy. The results indicate that the copper salts create more powerful interactions than the silver salts in the polymer matrix. DSC experiments reveal that the glass transition temperature of polymeric films containing silver or copper cations is lower than that of the PVP reference film. Comparison of the thermograms of PVP + AgNO₃ and PVP + Cu(NO₃)₂ shows that copper ions disrupt the polymer crystallinity more than silver ions. Therefore, DSC observations confirm the ATR‐FTIR results in the case of the strength of the complexes formed. A morphological analysis of membrane surfaces reveals the existence of electrostatic interactions in the polymeric membrane structure. This is a result of the addition of salt to the casting solution, wrinkling the polymer chains including the surface layer, and accordingly the surface of the facilitated transport membranes is rougher than the initial PVP membrane. Copyright © 2010 Society of Chemical Industry     

Hybrid Network Sulfonated Polynorbornene/Silica Membranes with Enhanced Proton Conductivity by Doped Phosphotungstic Acid

A series of novel hybrid sulfonated polynorbornene‐silica (PBN–SiO₂) proton conducting membranes doped with different weight ratio of phosphotungstic acid (PWA) were prepared by the casting procedure. The proton conductivity of the composite membranes containing 40 wt.% PWA reached the maximum of 6.1 × 10^–2 S cm^–1 and increased gradually with PWA content and temperature elevating, while the methanol permeabilities (3.52–9.39 × 10^–7 cm² s^–1) of these membranes were much lower than that of Nafion 117 (2.36 × 10^–6 cm² s^–1). The membranes also exhibited excellent thermally stable and mechanical properties, which imply that the PBN–SiO₂–PWA membranes are promising materials in the direct methanol fuel cells (DMFC) applications.     

Low velocity surface fracture patterns and energies in poly(methyl methacrylate)

Steady-state fracture techniques were used to investigate the surface fracture patterns and surface fracture energies of poly(methyl methacrylate) at low velocities (10 cm/sec to 10^?5 cm/sec). Several anomalies were discovered: (1) Small surface cracks, running parallel to the crack front, which were initiated by imperfections; (2) a “zero velocity” transition from the normal surface fracture patterns to a “laminar” pattern; and (3) a subsequent transition from the laminar pattern to a “turbulent” pattern. The velocities at which these anomalous fracture patterns occurred were of the order of 10^?4 to 10^?6 cm/sec. The corresponding surface fracture energies were as low as 10⁵ erg/cm².     

Diffusion coefficients of Br2, HNO3 and PdCl2 in graphite

Diffusion coefficients of HNO₃ and Br₂ from near-saturated vapor into highly oriented pyrolytic graphite at 30°C are respectively, 203 × 10^?6 cm²/min and 1.47 × 10^?6 cm²/min, and that of PdCl₂ is 0.52 × 10^?6 cm²/min at 450°C. Rapid diffusion of HNO₃ is attributed to its intercalation as a two-dimensional liquid, whereas bromine and PdCl₂ intercalate as two-dimensional solids. Estimated diffusion coefficients of alkali graphites, which also intercalate as two-dimensional solids, are smaller than those for Br₂ or PdCl₂, but transition metal chlorides which intercalate from the vapor above the bulk melting temperature have estimated diffusion coefficients comparable to those of HNO₃. Rates of intercalation are linear functions of $\text{(time)}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ until intercalation by HNO₃ is 80% complete and intercalation by Br₂ is at least 23% complete, and indicate that a single diffusion process controls each reaction even though gross compositions corresponding to the formation of discrete crystallographic “stages” are exceeded. This result accords well with structural models of intercalation compounds in which monolayer “rafts” of intercalant take up ordered positions throughout the bulk of a graphite crystal, but not with models, in which intercalant monolayers continuously cover basal planes. The apparent activation energy for diffusion of PdCl₂ in graphite, 35 kcal/mole, is attributed to a process which precedes diffusion.     

Characterization of polymeric LB thin films for sensor applications

The Quartz Crystal Microbalance (QCM) system is utilized to investigate the relationship between mass uptake and associated swelling for Langmuir‐Blodgett (LB) organic thin films obtained from pyrene end‐capped polystyrene (PS). The study was carried out using three different molecular weights of polymeric chains. The changes in resonance frequency associated with mass changes can be attributed to the swelling behavior of polymeric thin films during vapor absorption. This swelling is due to the capturing of organic vapor molecules in the sensor environment. To quantify real‐time QCM data for swelling, early‐time Fick's law of diffusion was adopted to fit the results, and a good linear relationship was observed between the mass uptake and square root of the swelling time. The diffusion coefficients for swelling were thus obtained from the slopes of the fitting curves and was found to be correlation with the amount of organic vapor content in the cell. It was also observed that diffusion of the organic vapor into higher molecular weight polystyrene thin films are much faster than low molecular weight ones in sensor applications. Diffusion coefficients were found to be 0.2–3.0 × 10^?16, 5.0–13 × 10^?16, and 1.0–1.6 × 10^?15 cm²/s for PS1, PS2, and PS3 LB thin films, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Behavior of sulfonated poly(ether ether ketone) in ethanol–water systems

The behavior of sulfonated poly(ether ether ketone) (sPEEK) membranes in ethanol–water systems was studied for possible application in direct ethanol fuel cells (DEFCs). Polymer membranes with different degrees of sulfonation were tested by means of uptake, swelling, and ethanol transport with dynamic measurements (liquid–liquid and liquid–gas systems). Ethanol permeability was determined in an liquid–liquid diffusion cell. For membranes with an ion‐exchange capacity (IEC) between 1.15 and 1.75 mmol/g, the ethanol permeability varied between 5 × 10^?8 and 1 × 10^?6 cm²/s, being dependent on the measuring temperature. Ethanol and water transport in liquid–gas systems was tested with pervaporation as a function of IEC and temperature. Higher IEC accounted for higher fluxes and lower water/ethanol selectivity. The temperature had a large effect on the fluxes, but the selectivity remained constant. Furthermore, the membranes were characterized with proton conductivity measurements. The proton diffusion coefficient was calculated, and a transition in the proton transfer mechanism was found at a water number of 12. Membranes with high IEC (>1.6 mmol/g) exhibited larger proton diffusion coefficients in ethanol–water systems than in water systems. The membrane with the lowest IEC exhibited the best proton transport to ethanol permeability selectivity. The use of sPEEK membranes in DEFC systems depends on possible modifications to stabilize the membranes in the higher conductive region rather than on modifications to increase the proton conductivity in the stable region. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CO2‐facilitated transport through poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate)/polysulfone composite membranes

Poly(N‐vinyl‐γ‐sodium aminobutyrate‐co‐sodium acrylate) (VSA–SA)/polysulfone (PS) composite membranes were prepared for the separation of CO₂. VSA–SA contained secondary amines and carboxylate ions that could act as carriers for CO₂. At 20°C and 1.06 atm of feed pressure, a VSA–SA/PS composite membrane displayed a pure CO₂ permeation rate of 6.12 × 10^?6 cm³(STP)/cm² s cmHg and a CO₂/CH₄ ideal selectivity of 524.5. In experiments with a mixed gas of 50 vol % CO₂ and 50 vol % CH₄, at 20°C and 1.04 atm of feed pressure, the CO₂ permeation rate was 9.2 × 10^?6 cm³ (STP)/cm² s cmHg, and the selectivity of CO₂/CH₄ was 46.8. Crosslinkages with metal ions were effective for increasing the selectivity. Both the selectivity of CO₂ over CH₄ and the CO₂ permeation rate had a maximum against the carrier concentration. The high CO₂ permeation rate originated from the facilitated transport mechanism, which was confirmed by Fourier transform infrared with attenuated total reflectance techniques. The performance of the membranes prepared in this work had good stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 275–282, 2006