Membrane Diffusion Coefficient Research Articles

Investigation and Technique of Calculating the Effective Operation Life of Semipermeable Membranes in Ultrafiltration Purification of Industrial Solutions

The design of a newly developed membrane device and technique of calculating the effective operation life of semipermeable ultrafiltration membranes by means of which the length of the period of effective realization of the process of purification, concentration and demineralization of industrial solutions may be determined is presented. In the newly developed technique, the estimated length of the effective life of ultrafiltration membranes under different conditions of the industrial purification process, which varies from 96 to 125 hours, is determined. Computed average calculated values of the diffusion coefficients in ultrafiltration membranes and the maximum contact stresses are presented.

The Ionic and Water Transport Properties Studies of Univalent Ion Exchanged Perfluorosulfonate Membrane

Perfluorosulfonic acid (PFSA) polymer membranes have been widely studied in the context of their applications as ion exchange medium/solid electrolytes in proton exchange membrane (PEM) fuel cells and other redox applications since 1970s(1). Water management plays a significant role in the performance of polymer membrane electrolytes, especially in fuel cells, because the ionic conductance dramatically decreases at low relative humidity, while excess water may flood the flow channels and hinder the transport of reagents such as gases (2). The conductivity and water diffusion coefficient of membranes therefore are always of concern because of their function in electrochemical devices. In this work, Li+, Na+, NH4 + and TEA+ form PFSA membranes were prepared based on H-form 3M PFSA membrane. The water uptake, density and conductivity of these membranes were investigated at various hydration levels. It’s found that the hydrophilicity of cations determines the water uptake of membranes with different cations, showing a series of water uptake in the order of: H+ > Li+ > Na+ > NH4 + > TEA+. As expected, H+ form membranes show the highest conductivity among all membrane forms due to the smallest charge carrier size and proton hopping transport mechanism. This mechanism may also contribute for NH4 + transport, resulting in a comparably high conductivity of NH4 + form membranes even though the latter take up much less water. Pulsed field gradient (PFG) Nuclear Magnetic Resonance (NMR) was exploited to observe the diffusion coefficient of water in the membranes. It was observed that hydrophilicity of cations and the hydrogen bonding interactions affect the water transport in the membranes. Based on density measurements, a partial molar volume analysis is carried out in this study. This parameter provides insight into the water and polymer interactions in various univalent PFSA membranes. Acknowledgement. We gretefully acknowledge the support of this work by the Office of Naval Research. We also appreciate the assistance of 3M company in providing 3M PFSA membrane samples.

Development of Anodic Stripping Voltammetry in Alkaline Electrolyte and Application for Screening Anion Diffusion Selectivity in Battery Separators

Anodic stripping voltammetry (ASV) is a well-known powerful, sensitive, and selective analysis technique used for the detection of metal ion species in solution. While ASV was initially developed with mercury (Hg) as the plating electrode more recent applications have used bismuth (Bi) as a less toxic and less oxygen sensitive electrode that has low background currents, better reproducibility, and little to no need for electrode conditioning, as compared to Hg electrodes. ASV is most commonly performed under neutral to acidic electrolyte conditions where metals, as metal cations are readily soluble; however, the extension of an ASV method into highly alkaline environments (pH > 14) could prove useful for the in situ electrolyte monitoring of alkaline batteries and fuel cells such that potential diagnostics of their performance vs. electrolyte composition could be realized. With this in mind, we recently extended the ASV method to highly alkaline electrolytes, in order to determine Zn diffusion across separator membranes.[1] Zinc (Zn) alkaline battery chemistries such as Zn/MnO2 and Zn/Air are currently attracting a lot of attention due to their potential as safe, low cost, high energy density rechargeable batteries. A main failure mechanism for these cells is the poisoning of the cathode material during cycling due to Zn crossover from the anode to the cathode. Advanced separators that successfully stop or limit this crossover are crucial in order to increase the cycle lifetime of these batteries. ASV, utilizing a Bi film, along with cadmium (Cd) and lead (Pb) as the plating mediators, was utilized to determine Zn concentrations in highly alkaline environments (30% NaOH or 35% KOH). To evaluate the utility of this assay, zincate diffusion through commercial off-the-shelf (COTS) Celgard 3501 and Cellophane 350P00 membranes was monitored using both ASV and inductively coupled plasma – mass spectrometry (ICP-MS) methods. The obtained zincate diffusion coefficients for both techniques are shown to compare favorably. While the traditional complexometric or elemental analysis methods can take days to weeks to determine Zn membrane diffusion metrics, this ASV method provides a real-time measurement which significantly increases the throughput for the screening of these membranes. During our development of an ASV method for Zn, we realized that in general there was a lack of ASV methods in highly alkaline electrolyte and hence turned our attention to the development of an ASV method for the determination of Cu, as cuprate [Cu(OH)4 2-]. Cu has been notoriously difficult to measure by ASV, even under acidic conditions.[2] In fact, most studies using Bi film electrodes for the direct determination of Cu have deemed it impossible and thus studies for the determination of the Cu concentration in a matrix are normally still performed separately with Hg electrodes. After investigation of potential metal film electrodes and mediators including Cd, Ag, Sb, and Zn, it was found that lead (Pb) serves as a good mediator for the plating of Cu in highly alkaline solutions which permits the replacement of the interfering Bi film electrode. Various aspects of this work will also be presented. [1]. J. Duay, T. N. Lambert and R. Aidun “Stripping Voltammetry for the Real Time Determination of Zinc Membrane Diffusion Coefficients in High pH: Towards Rapid Screening of Alkaline Battery Separators” Electroanalysis 2017, 29, 2261-2267. [2]. J. Duay, J. E. Ortiz-Santiago and T. N. Lambert “Copper Sensing in Alkaline Electrolyte Using Anodic Stripping Voltammetry by means of a Lead Mediator” Electroanalysis 2017, DOI: 10.1002/elan.201700526. This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability is also thanked for financial support of this project.

Water and Salt Transport Properties of Triptycene-Containing Sulfonated Polysulfone Materials for Desalination Membrane Applications.

A series of triptycene-containing sulfonated polysulfone (TRP-BP) materials was prepared via condensation polymerization, and the desalination membrane-relevant fundamental water and salt transport properties (i.e., sorption, diffusion, and permeability coefficients) of the polymers were characterized. Incorporating triptycene into sulfonated polysulfone increased the water content of the material compared to sulfonated polysulfone materials that do not contain triptycene. No significant difference in salt sorption was observed between TRP-BP membranes and other sulfonated polysulfone membranes, suggesting that the presence of triptycene in the polymer did not dramatically affect thermodynamic interactions between salt and the polymer. Both water and salt diffusion coefficients in the TRP-BP membranes were suppressed relative to other sulfonated polysulfone materials with comparable water content, and these phenomena may result from the influence of triptycene on polymer chain packing and/or free-volume distribution, which could increase the tortuosity of the transport pathways in the polymers. Enhanced water/salt diffusivity selectivity was observed for some of the TRP-BP membranes relative to those materials that did not contain triptycene, and correspondingly, incorporation of triptycene into sulfonated polysulfone resulted in an increase, particularly for acid counterion form TRP-BP materials, in water/salt permeability selectivity, which is favorable for desalination membrane applications.

Molecular dynamics simulation of oxygen transport characteristics in the electrolyte membrane of PEMFC

PurposeThis paper aims to investigate the oxygen transport characteristics in the electrolyte membrane of proton exchange membrane fuel cell (PEMFC), in particular, the water content dependence and the microscopic view of the molecular transport.Design/methodology/approachMolecular dynamics simulation is used to examine the oxygen transport characteristics in the electrolyte membrane of PEMFC that we have experimentally observed in our previous study.FindingsMolecular dynamics simulation well predicts the diffusion coefficient of oxygen in the membrane. It was found that the oxygen molecules have preference in their transport passage that governs the property.Originality/valueFirst attempt is to theoretically examine the experimentally observed water uptake dependence of the oxygen diffusion coefficient in membrane and to explain the mechanism.

Experimental and Numerical Investigation of Humidity Effect on Performance of PEM Fuel Cells

In this study, we conducted an experimental test to evaluate the performance of a PEM single cell at different humidity level of the reactants (i.e. hydrogen and air). The motivation was to use the test dataset to validate a simple numerical model which predict the I-V curve of the cell when the humidity is varied. We conducted the test using a 50cm2 single cell, five-layer membrane electrode assembly composed of a Nafion 211 membrane and carbon paper as GDL. Relative humidity (RH) was varied alternatively between 50 and 100 percent both at anode and cathode side. We found that the best cell performance was obtained when RH was fixed at 100% both at anode and cathode side. On the other hand, cell performance was particularly affected when relative humidity was reduced at the cathode side. This can be explained by the decrement of water diffusion from the cathode to anode and therefore a loss in electrical conductivity. The test also showed that humidity mainly affects Ohmic losses rather than activation or overpotential losses. Ohmic losses are mainly related to water hydration in polymer electrolyte membranes. The cell performance model considers only relationships for electro-osmotic drag, membrane ionic conductivity and diffusion coefficient of water in the membrane. Hydraulic permeability was neglected as the pressure difference between anode and cathode side was minimal during the test. Temperature, mass flow rate, and pressure were also important to estimate the water and mass balance. We fitted the model parameters to the test results and find out that cell ohmic resistance was the main relationship to be modulated at different humidity levels. In fact, there is a close link between water uptake, cell resistance, and membrane conductivity and thickness. The model simplicity was essential because the code was aimed to be implemented in a larger fuel cell system model. The model will come useful to develop a strategy for water management.

Effect of Surface Diffusion on Adsorption–Desorption and Catalytic Kinetics in Irregular Pores. II. Macro-Kinetics

In this work we show how the effective diffusion coefficient of a membrane, in which heterogeneous reaction-diffusion processes are present, is related to the geometric irregularity of the pores and how it is affected by the surface diffusion of an adsorbed phase. A theoretical expression for this effective membrane diffusion coefficient is deduced starting from a recent generalization of the so-called Fick–Jacobs approximation. Our analysis comprises the interrelation of bulk and surface diffusion with the heterogeneous catalysis and adsorption/desorption interchange of matter between the bulk and the walls of the pore. Therefore, our theoretical framework is a very useful tool in modeling the process of heterogeneous catalysis inside porous materials when the shape of the pores is known. Through some illustrative examples involving the classical Langmuir processes as a reference, we provide a useful methodology correlating the local properties of transport inside a pore of irregular shape with the effective diffusion coefficient of a membrane. This coefficient can be measured experimentally by fitting the spatio-temporal concentration profiles in adsorption experiments. We show the different dependencies of this coefficient with the surface diffusion, the shape of the pore, and the average loading of adsorbed particles. A reverse methodology is also sketched, in which we suggest how to use the data emerging from experiments in order to determine the intensity of the surface diffusivity.

Effect of Surface Diffusion on Adsorption–Desorption and Catalytic Kinetics in Irregular Pores. I. Local Kinetics

In this work we show how the effective diffusion coefficient of a membrane, in which heterogeneous reaction-diffusion processes are present, is related to the geometric irregularity of the pores and how it is affected by the surface diffusion of an adsorbed phase. A theoretical expression for this effective membrane diffusion coefficient is deduced starting from a recent generalization of the so-called Fick–Jacobs approximation. Our analysis comprises the interrelation of bulk and surface diffusion with the heterogeneous catalysis and adsorption/desorption interchange of matter between the bulk and the walls of the pore. Therefore, our theoretical framework is a very useful tool in modeling the process of heterogeneous catalysis inside porous materials when the shape of the pores is known. Through some illustrative examples involving the classical Langmuir processes as a reference, we provide a useful methodology correlating the local properties of transport inside a pore of irregular shape with the effec...

Improvement of MCDI operation and design through experiment and modelling: Regeneration with brine and optimum residence time

Membrane Capacitive Deionization (MCDI) is an energy efficient, electrochemical desalination technology, in which ions are removed from a salty stream upon applying a constant voltage or current. The ions are stored in carbon electrodes and then released back into the stream by reversing the polarity. In this work, we aimed to assess the feasibility of using a brine stream to regenerate the MCDI unit in order to improve water recovery. We further aimed to determine the optimum residence time in the MCDI unit. To achieve these objectives, we first enhanced the ion transport model previously developed for MCDI by independently measuring the counter-ion and co-ion diffusion coefficients in the ion-exchange membranes. These experiments allowed for an asymmetric model of the MCDI unit where the voltage drop across the cation exchange membrane was greater than that across the anion exchange membrane. Using this revised model, we found that in batch operation, a brine to feed water concentration ratio of around two was optimum. In continuous operation, over 40% enhancement in water recovery could be achieved when the regeneration brine was partially recycled, but water productivity dropped. We further showed that the maximum desalination capacity did not increase beyond a critical residence time in the MCDI cell, while the water recovery decreased.

Sorption, diffusion and pervaporation study of thiophene/ n -heptane mixture through self-support PU/PEG blend membrane

Abstract The novel polyurethane (PU)/polyethylene glycol (PEG) self-support blend membranes were prepared via solution casting method to investigate their gasoline desulfurization performance. Pervaporation (PV) method was employed to separate thiophene from model gasoline consisting of a binary mixture of thiophene and n -heptane. The membrane sorption (S) and diffusion (D) coefficients were obtained from the sorption test. Characteristics and morphological attributes of the membrane were studied using FTIR and SEM analysis. SEM images exhibited a fine heterogeneous blended phase with a defect-free surface. Blending intensified the properties of individual PU and PEG membranes bringing about satisfactory permeability and desulfurization performance. A normalized flux of 25.5 kg µm/m 2 h and an enrichment factor of 7.1 were obtained at 65 °C. The membranes were constructed and evaluated in self-support form, which indicates their mechanical and chemical strength when operated up to 120 h. Both the blending method and the selection of the proper PU with appropriate blending ratio resulted in the fabrication of apposite membranes for separation of thiophene from n -heptane and also the development of a membrane material to be utilized in desulfurization industry.

Accounting for frame of reference and thermodynamic non-idealities when calculating salt diffusion coefficients in ion exchange membranes

Accurate evaluation of salt diffusion coefficients from transport rate data in ion exchange membranes requires accounting for frame of reference and non-ideal thermodynamic effects. Due to a lack of models and experimental data quantifying membrane ion activity coefficients, it has been impossible to evaluate the impact of non-ideal thermodynamic effects on observed salt diffusion coefficients. Here, a framework is presented that includes both frame of reference (i.e., convection) and non-ideal thermodynamic effects in calculating salt diffusion coefficients in ion exchange membranes. Effective concentration averaged NaCl diffusion coefficients were determined as a function of upstream NaCl concentration in commercial ion exchange membranes from NaCl permeability and sorption measurements via the solution-diffusion model. Frame of reference effects were evaluated using a version of Fick's law that accounts for convection. The factors necessary to account for non-ideal thermodynamic effects were developed using Manning's counter-ion condensation theory. At low upstream NaCl concentrations, frame of reference and non-ideal thermodynamic effects on diffusion coefficients were negligible. However, at higher upstream NaCl concentrations (e.g., >0.1M), both effects contribute measurably to NaCl diffusion coefficients. Correcting for frame of reference effects increased apparent NaCl diffusion coefficients. However, correcting for thermodynamic non-idealities of the ions sorbed into the membranes reduced apparent NaCl diffusion coefficients. Fortuitously, for the materials considered in this study, frame of reference and non-ideal thermodynamic effects nearly cancel each other.

Single Cell Examination of Membrane Fluidity and Cellular Respiration

Bulk measurements of oxygen consumption rates by bacteria have previously been shown to be related to the cells' average membrane fluidity (as measured by the diffusion of fluorescently-labeled molecules). Within a bacterial population, there is also significant cell-to-cell variation in both the diffusion coefficient of membrane probes and oxygen consumption rates of individual cells. One possibility is the diffusion of ubiquinone, an electron carrier in the electron transport chain (ETC), is being limited by the fluidity of the membrane which is causing the heterogeneity.We describe Fluorescence Recovery After Photobleaching (FRAP) measurements to monitor cell-to-cell variation in membrane diffusion coefficient. These results are compared to two approaches to look at what influence it might have on respiration at the single cell level. The first uses a fluorescent indicator of the activity of the ETC. The second directly measures the consumption of oxygen by individual cells using a phosphorescent Pt-porphyrin dye.

Voltammetric determination of diffusion coefficients in polymer membranes.

The diffusion-controlled transport of ions and molecules through polymer membranes utilized in chemical and biosensors is often the key factor determining the response characteristics of these sensors. In this paper, a simple voltammetric method is described for the determination of diffusion coefficients of redox molecules in resistive polymer membranes using a planar electrochemical cell (PEC) with a 5 μm radius carbon fiber as working electrode. In the proposed method, the diffusion coefficients are assessed from the scan rate dependence of the peak (or limiting) currents in linear sweep or cyclic voltammograms. The accuracy of the method is estimated through simulations using the method of Nicholson and Shain describing the quantitative relationship between the measured peak current (ip) and the square root of the scan rate (v1/2). The proposed method has been used for measuring the diffusion coefficients of ferrocene derivatives in highly resistive aqueous solutions, organic solvents, plasticizers, and plasticized PVC membranes. The measured diffusion coefficients are in agreement with theoretical models and previously reported values.

Voltammetric Thin-Layer Ionophore-Based Films: Part 2. Semi-Empirical Treatment.

This work reports on a semiempirical treatment that allows one to rationalize and predict experimental conditions for thin-layer ionophore-based films with cation-exchange capacity read out with cyclic voltammetry. The transition between diffusional mass transport and thin-layer regime is described with a parameter (α), which depends on membrane composition, diffusion coefficient, scan rate, and electrode rotating speed. Once the thin-layer regime is fulfilled (α = 1), the membrane behaves in some analogy to a potentiometric sensor with a second discrimination variable (the applied potential) that allows one to operate such electrodes in a multianalyte detection mode owing to the variable applied ion-transfer potentials. The limit of detection of this regime is defined with a second parameter (β = 2) and is chosen in analogy to the definition of the detection limit for potentiometric sensors provided by the IUPAC. The analytical equations were validated through the simulation of the respective cyclic voltammograms under the same experimental conditions. While simulations of high complexity and better accuracy satisfactorily reproduced the experimental voltammograms during the forward and backward potential sweeps (companion paper 1), the semiempirical treatment here, while less accurate, is of low complexity and allows one to quite easily predict relevant experimental conditions for this emergent methodology.

The Use of Cellulose Membrane to Eliminate Burst Release from Intravaginal Rings.

Burst release was observed when ethylene vinyl acetate copolymer (EVA) intravaginal rings were tested for progesterone release in our previous work (Helbling et al. Pharm Res. 31(3):795-808, 2014). Burst release is undesirable in controlled delivery devices because release is uncontrollable and higher levels of active pharmaceutical ingredient could lead to the occurrence of adverse effect. The present contribution is about the use of membranes to coat EVA rings to eliminate burst release. Physicochemical state of progesterone in uncoated rings and the solubility and diffusion coefficient in membrane were studied. Hormone delivery from several rings of different sizes was compared. A mathematical model was used to analyze the effects of membrane properties on delivery rate. No chemical interactions were detected between hormone and polymer. Hormone was mainly forming amorphous aggregates inside rings, and migration to membrane was not observed during storage. Diffusion coefficient was smaller in membrane (∼10(-8)cm(2)s(-1)) than in matrix (∼10(-7)cm(2)s(-1)). Zero-order release kinetics were obtained for coated rings, and release rate decreases as the thickness of the coat increases. Cellulose membrane successfully eliminates burst release and controls the delivery from EVA rings. The equations developed can be used to determine the appropriate coat thickness to produce specific release rate.

Diffusion And Osmosis In Potassium Nitrate Synthesis By Electrodialysis Metathesis

Abstract The experimental results of the chosen salts permeation with selected heterogeneous and homogenous membranes were analysed as a part of modelling of mass transport in electrodialysis metathesis process (ED-M) for synthesis of KNO3. Heterogeneous membranes swelled more in aqueous solutions and they had higher water uptake than homogeneous membranes. Heterogeneous membranes were also more permeable for both the solute and the solvent, which was attributed to higher solubility of salts in heterogeneous membrane’s material. Diffusion coefficients in ion-exchange membranes tested in this study were found to be dependent on concentration of the upstream solution, with an exception of Ca2+ in anion-exchange membranes and NO3- in cation-exchange membranes. The role of osmosis in water transport in ED-M process was found negligible.

Fabrication of a tunable hydrogel membrane for constructing indirect cell coculture system

ABSTRACTIn this study, an improved indirect cell coculture system was constructed by using a polyelectrolyte complex membrane generated by alginate (A) and chitosan (C). Methodologies of characterizing thickness and permeability of flat AC membrane were first established due to the importance of these two parameters in determining intercellular distance and degree of contact between cocultured cells. Compared to reaction time, both alginate concentration and molecular weight (Mw) of chitosan play more dominant roles in determining the membrane thickness and diffusion coefficients. Moreover, cells in the alginate gel and on the AC membrane could maintain high cell viability. Thus, an improved indirect cell coculture system constructed by flat AC membrane was fabricated and characterized, which provides a robust tool to study the effect of intercellular distance and degree of contact between cocultured cells on cell–cell interactions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43100.

Methanol catalytic micro-combustor with pervaporation-based methanol supply system

A catalytic micro-combustor using a pervaporation membrane as the passive methanol vaporizer is developed for direct methanol fuel cell (DMFC) applications, which is able to realize self-starting in an ambient environment. The methanol feed rate and the membrane diffusion coefficient related to the permeation flux are experimentally evaluated. Results indicate that the air feed rate (AFR) has positive effects on enhancing the methanol production and also increasing the catalyst temperature. A higher AFR promotes vapor generation and improves the combustion rate, thereby facilitating a higher start-up performance of the combustor. The infrared thermal analysis verifies the positive effect of increasing the AFR on the status of heat production and distribution. Results also validate the feasibility of changing the operating orientation of the combustor, which illuminates its potential use for portable applications. The online fuel cell tests validate that this combustor is viable to be used as a heat generator for a vapor-feed DMFC.

Opposing Effects of cAMP and T259 Phosphorylation on Plasma Membrane Diffusion of the Water Channel Aquaporin-5 in Madin-Darby Canine Kidney Cells.

Aquaporin-5 (AQP5) facilitates passive water transport in glandular epithelia in response to secretory stimuli via intracellular pathways involving calcium release, cAMP and protein kinase A (PKA). In epithelial plasma membranes, AQP5 may be acutely regulated to facilitate water transport in response to physiological stimuli by changes in protein modifications, interactions with proteins and lipids, nanoscale membrane domain organization, and turnover rates. Such regulatory mechanisms could potentially be associated with alteration of diffusion behavior, possibly resulting in a change in the plasma membrane diffusion coefficient of AQP5. We aimed to test the short-term regulatory effects of the above pathways, by measuring lateral diffusion of AQP5 and an AQP5 phospho-mutant, T259A, using k-space Image Correlation Spectroscopy of quantum dot- and EGFP-labeled AQP5. Elevated cAMP and PKA inhibition significantly decreased lateral diffusion of AQP5, whereas T259A mutation showed opposing effects; slowing diffusion without stimulation and increasing diffusion to basal levels after cAMP elevation. Thus, lateral diffusion of AQP5 is significantly regulated by cAMP, PKA, and T259 phosphorylation, which could be important for regulating water flow in glandular secretions.

Fundamental Studies of Ion Sorption, Diffusion and Transport in Polyelectrolyte Membranes

Charged polymer membranes are widely used for water purification applications involving control of water and ion transport, such as reverse osmosis and electrodialysis, as well as applications such as fuel cell membranes. Efforts are also underway worldwide to harness separation properties of such materials for energy generation in related applications such as reverse electrodialysis and pressure retarded osmosis. Improving membranes for such processes would benefit from more complete fundamental understanding of the relation between membrane structure and ion sorption, diffusion and transport properties in both cation and anion exchange membrane materials. Ion-exchange membranes often contain strongly acidic or basic functional groups that render the materials hydrophilic, but the presence of such charged groups has a substantial impact on ion (and water) transport properties. This presentation will discuss aspects of chemistry, thermodynamics, and transport that are or may be at play in such membrane processes. Our long-term goal is to develop and validate a common framework to interpret data from both electrically driven and concentration gradient driven mass transport in such polymers and to use it to establish structure/property relations leading to rational design of membranes with improved performance. Questions of interest include how to properly formulate sorption and transport relationships, how to decouple effects of fixed charge density and water content on sorption and transport properties, how fixed charges affect mobility of counterions and coions, etc. Ion sorption and permeability data were used to extract information about salt diffusion coefficients in charged membranes. Techniques have been developed to determine concentrations of both counter-ions and co-ions in polymers. Salt permeability, sorption and ionic conductivity data have been combined to determine individual ion diffusion coefficients in neutral, cation exchange and anion exchange polymers. The use of models to correlate and, in many cases, predict the experimental data is discussed.