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Factors affecting the swelling of cellulosic fibers are considered in this review. Emphasis is placed on aqueous systems and papermaking fibers, but the review also considers cellulose solvent systems, nanocellulose research, and the behavior of cellulosic hydrogels. The topic of swelling of cellulosic fibers ranges from effects of humid air, continuing through water immersion, and extends to hydrogels and the dissolution of cellulose, as well as some of its derivatives. The degree of swelling of cellulose fibers can be understood as involving a balance between forces of expansion (especially osmotic pressure) vs. various restraining forces, some of which involve the detailed structure of layers within the fibril structure of the fibers. The review also considers hornification and its effects related to swelling. The expansive forces are highly dependent on ionizable groups, pH, and the ionic strength of solution. The restraining forces depend on the nature of lignin, cellulose, and their detailed structural arrangements.

Diffusiophoresis is the isothermal migration of a colloidal particle through a liquid caused by a cosolute concentration gradient. Although diffusiophoresis was originally introduced using hydrodynamics, it can also be described by employing the framework of multicomponent diffusion. This not only enables the extraction of diffusiophoresis coefficients from measured multicomponent-diffusion coefficients but also their theoretical interpretation using fundamental thermodynamic and transport parameters. This review discusses the connection of diffusiophoresis with the 2 × 2 diffusion-coefficient matrix of ternary liquid mixtures. Specifically, diffusiophoresis is linked to the cross-term diffusion coefficient characterizing diffusion of colloidal particles due to cosolute concentration gradient. The other cross-term, which describes cosolute diffusion due to the concentration gradient of colloidal particles, is denoted as osmotic diffusion. Representative experimental results on diffusiophoresis and osmotic diffusion for polyethylene glycol and lysozyme in the presence of aqueous salts and osmolytes are described. These data were extracted from ternary diffusion coefficients measured using precision Rayleigh interferometry at 25 °C. The preferential-hydration and electrophoretic mechanisms responsible for diffusiophoresis are examined. The connection of diffusiophoresis and osmotic diffusion to preferential-interaction coefficients, Onsager reciprocal relations, Donnan equilibrium and Nernst–Planck equations are also discussed. [ABSTRACT FROM AUTHOR]

The capillaries are the 'business end' of the circulatory system, where materials exchange between the plasma and tissues. Water-soluble molecules can diffuse through pores in the capillaries, and a Gibbs–Donnan equilibrium exists between the plasma and interstitium. There are several types of capillaries, which vary in their anatomical integrity and permeability. There is also a bulk flow of fluids between the plasma and interstitium, described by the Starling forces. Originally, these forces were thought to cause fluids to leave the capillaries at the arteriolar end and return at the venular end; the role of the lymphatics was to provide an 'overflow' mechanism due to protein leakage out of the capillaries. More recent work indicates that this concept needs modification. Lymph flow and interstitial colloidal osmotic pressure are now known to be greater than first thought, and the interstitium has a slightly negative hydrostatic pressure. It is now believed that filtration takes place along most of the capillary, and the lymphatic system plays a more important role in maintaining plasma–interstitium equilibrium and preventing oedema. The system acts as a 'closed' one in that the changes in fluid formation (e.g. following haemorrhage or cardiac failure) are self-limiting. However, in some circulations (e.g. those to the kidneys, glands and the gut), net fluid production or absorption is required. This requirement is fulfilled by an independence from the Starling forces, the systems behaving as 'open' ones. [ABSTRACT FROM AUTHOR]

Diffusiophoresis is the isothermal migration of a colloidal particle through a liquid caused by a cosolute concentration gradient. Although diffusiophoresis was originally introduced using hydrodynamics, it can also be described by employing the framework of multicomponent diffusion. This not only enables the extraction of diffusiophoresis coefficients from measured multicomponent-diffusion coefficients but also their theoretical interpretation using fundamental thermodynamic and transport parameters. This review discusses the connection of diffusiophoresis with the 2 × 2 diffusion-coefficient matrix of ternary liquid mixtures. Specifically, diffusiophoresis is linked to the cross-term diffusion coefficient characterizing diffusion of colloidal particles due to cosolute concentration gradient. The other cross-term, which describes cosolute diffusion due to the concentration gradient of colloidal particles, is denoted as osmotic diffusion. Representative experimental results on diffusiophoresis and osmotic diffusion for polyethylene glycol and lysozyme in the presence of aqueous salts and osmolytes are described. These data were extracted from ternary diffusion coefficients measured using precision Rayleigh interferometry at 25 °C. The preferential-hydration and electrophoretic mechanisms responsible for diffusiophoresis are examined. The connection of diffusiophoresis and osmotic diffusion to preferential-interaction coefficients, Onsager reciprocal relations, Donnan equilibrium and Nernst–Planck equations are also discussed.

Mineral precipitation at interfaces between contrasting materials and porewaters decreases the local porosity and consequently reduces transport across the interface. The near-field of waste repositories usually contains reactive interfaces, and the long-term evolution of diffusive transport away from the waste across the near-field is of special interest in this context. Diffusion as well as further mineral reactions significantly slow down when complete porosity clogging is approached, such that any further development is difficult to detect in experiments. But ongoing diffusion, even if very limited, might be significant for relevant times of up to 1 million years. If clogging occurs in clay materials, experimental studies report a much stronger decrease in anion diffusion compared to that of cations or neutral species. Continuum-scale reactive transport codes can predict experimentally observed clogging, but rely on specific implementations based on conceptual assumptions. Typically, the codes calculate porewater-mineral reactions only within a single cell, and they neglect the physical contact of the clogging mineral in one cell with the porewater in an adjacent cell (no inter-cell reactions considered). This can lead to unrealistic model predictions if porosity approaches zero. For instance, neutral pH porewater is permitted to be in contact with clogging cement hydrates in the adjacent cell, and the implied dissolution of the high-pH minerals is not considered anymore. Thus, intrinsically reactive minerals can be converted erroneously into inert, relict phases by such models. We present a new approach that mimics inter-cell reactions. In doing so, clogging is substantially delayed, and no real steady state with the boundary conditions can be attained, in contrast to conventional approaches. Furthermore, we use a dual-porosity reactive transport approach that takes into account the electrostatic effects of charged clay surfaces on diffusion and precipitation, and apply it to concrete-clay interaction. No complete clogging of the pore space occurs, and the predictions well fit experimental data. Modelling studies that predict the separation of a reactive system into two domains by localised full porosity clogging, followed by separate internal equilibration of the domains, are widespread in the literature. This prediction is interpreted as a conceptual artefact of continuum-scale modelling, which should be avoided by allowing for reactions of completely clogged cells with adjacent porewater. For clays, the dual-porosity model may be a viable option in this respect. • Transport and reactions stop in completely clogged cells of conventional models. • No reaction between clogging minerals and adjacent porewater in the blocked pathway. • New implementations are suggested to circumvent this continuum-scale model artefact. • A dual-porosity model approach avoids this model artefact in clay. [ABSTRACT FROM AUTHOR]

Pre-dehydration of collagen-based hydrogel can result in reduced energy consumption in their large-scale production. This article reported a method to dehydrate collagen hydrogel by simply immersing hydrogel into sodium carboxymethylcellulose (CMC) solution, and the dehydration regularity and possible dehydration mechanisms were investigated. Collagen hydrogel was dehydrated in CMC solution with a dehydration rate of up to 68%, which favored the subsequent drying process as the drying time reduced by at least 18%. The CMC concentration, degree of substitution (DS), molecular weight (MW), and immersion time were all important factors affecting dehydration performance. The main dehydration mechanism was shown to be the Donnan equilibrium, which was attributed to the semi-permeability of the collagen hydrogel and the osmotic pressure difference at the interface induced by the CMC. Low MW CMC was able to penetrate into collagen hydrogel while high MW CMC was still difficult in penetrating into collagen hydrogel even in prolonged immersion time. Moreover, CMC-induced dehydration did not change the collagen fiber structures. This study provides a new pathway for the pre-dehydration of collagen-based materials, and also can help the design of collagen gel materials. [Display omitted] • Collagen hydrogel dehydrated in CMC solutions. • Apparent decrease of dehydration rate occurred in prolonged immersion time. • Donnan equilibrium was the principal cause of dehydration. • Low MW CMC was able to penetrated into CMC hydrogel. [ABSTRACT FROM AUTHOR]

This article first outlines definitions and descriptions of key terms that will be used in the discussions that follow, including osmolarity, osmolality, osmotic and oncotic pressure. The physicochemical properties of water, ions and organic molecules are discussed in terms of their biological roles. Similarly, the interactions of amphipathic molecules and their three-dimensional structures in aqueous and non-aqueous environments are then explored. The movement of solutes and solvents across semipermeable membranes is considered and an assessment is made of the contribution of such mechanisms to normal physiology. Firstly, simple diffusion is described, followed by comparisons with facilitated diffusion and energy-dependent active transport focusing on the differences in kinetics and rate-limiting factors arising as a result. The mechanisms underlying Gibbs–Donnan equilibria are discussed, with particular emphasis as to how they arise across a selectively permeable membrane by way of a worked example. The equilibrium of forces influencing fluid movements across the capillary endothelium, known as Starling forces, is then described. Comparisons are made between the classic model as first proposed by Starling in 1896 and the modified glycocalyx model, which has developed over the past 25 years. Finally, the impact of these differences on our understanding of trans-capillary fluid flux is discussed. [ABSTRACT FROM AUTHOR]

The equilibrium properties of ionic microgels are investigated using a combination of the Poisson- Boltzmann and Flory theories. Swelling behavior, density profiles, and effective charges are all calculated in a self-consistent way. Special attention is given to the effects of salinity on these quantities. In accordance with the traditional ideal Donnan equilibrium theory, it is found that the equilibrium microgel size is strongly influenced by the amount of added salt. Increasing the salt concentration leads to a considerable reduction of the microgel volume, which therefore releases its internal material - solvent molecules and dissociated ions - into the solution. Finally, the question of charge renormalization of ionic microgels in the context of the cell model is briefly addressed. [ABSTRACT FROM AUTHOR]

Involvement of thermodynamically-stable prenucleation clusters (PNCs) in the biomineralization of collagen has been speculated since their existence was reported in mineralization systems. It has been hypothesized that intrafibrillar mineralization proceeds via nucleation of inhibitor-stabilized intermediates produced by liquid-liquid separation (aka. polymer-induced liquid precursors; PILPs). Here, the contribution of PNCs and PILPs to calcium phosphate intrafibrillar mineralization of collagen was examined in a model with a semipermeable membrane that excludes nucleation inhibitor-stabilized PILPs from reaching the collagen fibrils, using cryogenic electron microscopy of reconstituted fibrils and conventional transmission electron microscopy of collagen sponges. Molecular dynamics simulation with the Interface force field (IFF) was used to confirm the existence of PILPs with amorphous calcium phosphate and elucidate details of the dynamics. Furthermore, intrafibrillar mineralization of single collagen fibrils was experimentally observed with unstabilized PNCs when anionic/cationic polyelectrolytes were used to establish Donnan equilibrium across the semipermeable membrane. Molecular dynamics simulation verified PNC formation within the collagen intrafibrillar gap zones at the atomic scale and explained the role of external PILPs. The PILPs decrease the interfibrillar water content and increase the interfibrillar ionic concentration. Nevertheless, intrafibrillar mineralization of collagen sponges with PNCs alone was inefficacious, being constrained by competition from extrafibrillar mineral precipitation. Compared with conventional PILP-based intrafibrillar mineralization, mineralization of collagen fibrils using unstabilized PNCs is constrained by competition from extrafibrillar mineral deposition. The narrow window of opportunity for PNCs to produce intrafibrillar mineralization provides a plausible explanation for the feasibility of nucleation inhibitor-free intrafibrillar apatite assembly during reconstitution of type I collagen. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The capillaries are the 'business end' of the circulatory system, where materials exchange between the plasma and tissues. Water-soluble molecules can diffuse through pores in the capillaries, and a Gibbs–Donnan equilibrium exists between the plasma and interstitium. There are several types of capillaries, which vary in their anatomical integrity and permeability. There is also a bulk flow of fluids between the plasma and interstitium, described by the Starling forces. Originally, these forces were thought to cause fluids to leave the capillaries at the arteriolar end and return at the venular end; the role of the lymphatics was to provide an 'overflow' mechanism due to protein leakage out of the capillaries. More recent work indicates that this concept needs modification. Lymph flow and interstitial colloidal osmotic pressure are now known to be greater than first thought, and the interstitium has a slightly negative hydrostatic pressure. It is now believed that filtration takes place along most of the capillary, and the lymphatic system plays a more important role in maintaining plasma–interstitium equilibrium and preventing oedema. The system acts as a 'closed' one in that the changes in fluid formation (e.g. following haemorrhage or cardiac failure) are self-limiting. However, in some circulations (e.g. those to the kidneys, glands and the gut), net fluid production or absorption is required. This requirement is fulfilled by an independence from the Starling forces, the systems behaving as 'open' ones. [ABSTRACT FROM AUTHOR]

An allegedly anomalous behaviour of aqueous dispersions of silica has attracted continually a great attention from Thomas Graham's time. However, even recent coagulation experiments with apparently well-defined colloidal silica spheres are not interpretable when their surface is assumed intact in contact with water. In fact, various explanations such as a hairy layer of polysilicic acid and the hydration layer on the silica surface are well-known but not proven accompaniments of the hydration process. It has been previously suggested (Skvarla, J., Langmuir, 29:8809–8824, 2013) basing on a combination of the soft-sphere model of colloids, surface charge data, and the Flory-Donnan theory that a swellable polyelectrolyte gel-like layer develops inherently on the surface of highly charged silica in aquoeus KCl solutions. Here, we support this rationalization by extending the coagulation analysis. Results are also discussed from the standpoint of approaches associated with the traditional and extended DLVO theories. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs), a promising technology for large-scale power grid energy storage, utilize a membrane separator to facilitate an ionic current while preventing mixing of the anolyte and catholyte solutions. The anolyte and catholyte of an RFB each contain an electroactive species, and usually an additional supporting electrolyte to charge balance the anode and cathode redox reactions and reduce overall ohmic losses. This study investigates the impact of the supporting electrolyte concentration and composition on Nafion's transport properties using permanganate as the permeant. The permanganate concentration was kept constant at 0.1 m , while sodium chloride and sodium hydroxide were both studied as supporting electrolytes. The sodium chloride concentration was varied from 0.1 m to 4.0 m , while the sodium hydroxide concentration was varied from 0.1 m to 10 m. The permanganate permeability, water sorption coefficient, and salt sorption coefficients were measured for Nafion, with a peak permeability being observed at a supporting electrolyte concentration of 1 m for both electrolytes. A framework to describe the observed behavior was derived using first principles to determine the transport coefficients under these conditions. It was found that at low concentrations, the permanganate permeability is controlled by Donnan exclusion and salt sorption, while at high concentrations it is controlled by salt diffusion and osmotic deswelling. [Display omitted] • The permeability of permanganate has a maximum with supporting electrolyte concentration. • At low supporting electrolyte concentrations, the permeability of permanganate is controlled by salt sorption due to the Donnan equilibrium. • At high supporting electrolyte concentrations, the permeability of permanganate is controlled by diffusion due to osmotic deswelling. • Nafion is more selective towards chloride co-ions over permanganate co-ions. [ABSTRACT FROM AUTHOR]

Cell membrane potential and inorganic ion distributions are currently viewed from a kinetic electric paradigm, which ignores thermodynamics. The resting membrane potential is viewed as a diffusion potential. The 9 major inorganic ions found in blood plasma (Ca2+, Na+, Mg2+, K+, H+, Cl-, HCO3-, H2PO4-, and HPO42-) are distributed unequally across the plasma membrane. This unequal distribution requires the energy of ATP hydrolysis through the action of the Na+-K+ ATPase. The cell resting membrane potential in each of 3 different tissues with widely different resting membrane potentials has been shown to be equal to the Nernst equilibrium potential of the most permeant inorganic ion. The energy of the measured distribution of the 9 major inorganic ions between extra- and intracellular phases was essentially equal to the independently measured energy of ATP hydrolysis, showing that the distribution of these 9 major ions was in near-equilibrium with the ΔG' of ATP. Therefore, thermodynamics does appear to play an essential role in the determination of the cell resting membrane potential and the inorganic ion distribution across the plasma membrane. [ABSTRACT FROM AUTHOR]

Abstract: A mathematical model based on a generalized Maxwell-Stefan equation has been developed to describe multicomponent ion and water transport inside a cation-exchange membrane. This model has been validated using experimental data and has been used to predict concentration profiles, membrane potential drop, and transport numbers of ions and water for the chlor-alkali process at increased current densities. Several improvements have been made to previously developed Maxwell-Stefan models. In our model, the generalized Maxwell-Stefan equation is written in terms of concentration instead of mole fraction and the fixed group (membrane) concentration is assumed to be constant. We have adapted the Augmented matrix method using the built-in partial differential equation parabolic elliptic (pdepe) solver in Matlab®, and both the concentration and the electrical potential gradients have been solved simultaneously. The boundary conditions are determined with the Donnan equilibrium at the membrane-solution interface. We have also employed semi-empirical correlations to define the Maxwell-Stefan diffusivities inside the membrane. For the bulk diffusivities, we applied the correlations for the concentrated solution instead of the values at infinite dilution. With the diffusivities presented in this work, the model shows a better fit to the experimental data than with previously reported fitted diffusivities. Prediction of the sodium transport number and water transport number is generally good, whereas the deviations with regard to membrane potential might also be related to issues with the experimental data. The model predicts an increase in both sodium and water transport numbers at increased current density operation of chlor-alkali production.Graphical abstract: [ABSTRACT FROM AUTHOR]

Cellulose–chitosan films were prepared using a physical method in which cellulose and chitosan were separately dissolved via freeze thawing in LiOH/urea and mixed in different proportions, the resulting films being cast and regenerated in water/ethanol. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) spectroscopy verified the composition changes in the nanocomposites due to different mixing ratios between the polymers. Tensile stress–strain measurements indicated that the mechanical performance of the cellulose–chitosan nanocomposites slightly worsened with increasing chitosan content compared with that of films comprising cellulose alone. Field emission scanning electron microscopy revealed the spontaneous formation of nanofibers in the films; these nanofibers were subsequently ordered into lamellar structures. Water uptake and microscopy analysis of film thickness changes indicated that the swelling dramatically increased at lower pH and with increasing chitosan content, this being ascribed to the Gibbs–Donnan effect. Slow material loss appeared at acidic pH, as indicated by a loss of weight, and quantitative FT-IR analysis confirmed that chitosan was the main component released. A sample containing 75% chitosan reached a maximum swelling ratio and weight loss of 1500% and 55 wt%, respectively, after 12 h at pH 3. The study presents a novel way of preparing pH-responsive cellulose–chitosan nanocomposites with slow-release characteristics using an environmentally friendly procedure and without any chemical reactions. [ABSTRACT FROM AUTHOR]

Abstract We report on a novel DNA affinity biosensor which utilises the capture of a neutral charged single stranded (ss) morpholino DNA on a gold electrode to trigger an electrostatic repulsion of negatively charged silicotungstate anions and, in turn, enabled detection of the hybridisation of complementary base pairs. The repulsion of the anions, as a redox indicator, is reflected by a decrease in its electrochemical response with increasing target ss-DNA concentration. A theoretical framework for DNA detection by the affinity biosensor is proposed and verified by electrochemical measurements in the presence of the target ss-DNA by either dc cyclic voltammetry or Fourier transformed alternating current voltammetry (FTACV). The optimised conditions for the capture of the target ss-DNA and the electrochemical detection include 1 μM thiolated neutral morpholino oligo-nucleotide probe, hybridisation time of 10 min, 0.25 mM [α-SiW 12 O 40 ]4-, and 25 mM phosphate buffer. In addition, the use of the 5th harmonic component of the FTACV gave the most sensitive response for the detection of the target ss-DNA. Under these conditions, the DNA affinity biosensor, based on FTACV detection, achieved a minimum detectable concentration of 0.1 pM ss-DNA and a linear concentration range of 0.1–1000 pM. The biosensor also successfully distinguished between some matched and mismatched base pairs. Graphical abstract fx1 Highlights • Hybridisation of complementary base pairs via the capture of a single stranded morpholino DNA. • Detection of hybridisation by the triggered repulsion of silicotungstate anions from electrode. • Proposal and verification of the theoretical basis for the operation of the DNA affinity biosensor. • Achievement of a minimum detectable concentration of 0.1 pM ss-DNA and a linear range of 0.1–1000 pM. • Selectively distinction between matched and mismatched sequences by the DNA affinity biosensor. [ABSTRACT FROM AUTHOR]

[Display omitted] • The DD-MS hybrid process saved 32.7% alkali and 34.9% acid during ammonium nitrogen recovery from landfill leachate. • Extra chemical consumption during the DD-MS process depends on bicarbonate concentration in the wastewater and sodium hydroxide concentration in the draw solution. • The reduction rate of chemical consumption increases with increasing bicarbonate concentration in the wastewater. Wastewater ammonium nitrogen (NH 4 +-N) recovery is frequently associated with massive and ineffective chemical consumption due to the presence of bicarbonate (HCO 3 –), resulting in undesirable economic feasibility. In the present study, by incorporating energy-efficient Donnan dialysis (DD) as a pretreatment process for membrane stripping (MS), we developed a low-chemical consumption hybrid DD-MS process with two membranes (cation exchange membrane [CEM] and hydrophobic membrane) and three phases (wastewater, draw solution and acid solution). First, equimolar amount of ammonium was exchanged with sodium ions and passed through CEM into an alkaline draw solution, where it was immediately deprotonated to free ammonia. Finally, it was diffused across a hydrophobic membrane, absorbed by the acid solution, and recovered as an ammonium salt. Meanwhile, HCO 3 – was confined to wastewater due to electrostatic repulsion from CEM. Owing to the chemical potential difference, NaOH in the draw solution diffused into the wastewater, resulting in additional chemical consumption. Experiments and calculations based on the Donnan equilibrium revealed that using an alkaline draw solution at a slightly higher concentration than that of wastewater ammonium allowed high NH 4 +-N recovery and low NaOH diffusion simultaneously. In experiments on actual landfill leachate, the hybrid DD-MS process achieved 81.4% NH 4 +-N recovery from wastewater while reducing alkali and acid consumption by respectively 32.7% and 34.9% compared with the conventional MS process. The hybrid process reduced the cost of chemicals and amount of salt entering the wastewater and environment. Overall, the proposed hybrid process presents excellent application prospects for NH 4 +-N recovery from wastewater with high-strength HCO 3 –, such as landfill leachate and livestock wastewater. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the ability of a recently proposed thermodynamic framework (i.e., Donnan/Manning model) to quantify equilibrium ion partitioning between aqueous salt solutions and inhomogeneous (i.e., phase separated) ion exchange membranes. Two inhomogeneous cation exchange membranes (CEMs) and one homogeneous anion exchange membrane (AEM), which served as a basis for comparison, were synthesized via free radical polymerization. Surface characterization of the membranes via cryogenic scanning electron microscopy revealed the inhomogeneous structure of the CEMs and the reasonably homogeneous structure of the AEM. Equilibrium ion concentrations in membranes equilibrated with NaCl, KCl, or MgCl 2 solutions were experimentally measured. The experimental results were interpreted via a thermodynamic model based on Donnan theory and Manning's counter-ion condensation theory. The framework predicted NaCl partitioning in the AEM, presumably due to its reasonably homogeneous structure, but failed to predict NaCl partitioning in the CEMs when the Manning parameter, ξ , was calculated assuming a homogeneous membrane. For the inhomogeneous CEMs, the Manning parameter was used as an adjustable constant, which was extracted from the NaCl sorption results. Remarkably, the value of ξ obtained from the NaCl sorption results accurately predicted KCl and MgCl 2 sorption in the two CEMs over the entire salt concentration range considered. Graphical abstract Unlabelled Image Highlights • Inhomogeneous ion exchange membranes synthesized via free radical polymerization. • Equilibrium NaCl, KCl, MgCl 2 sorption in membranes measured experimentally. • Ion sorption data interpreted via Donnan/Manning thermodynamic model. • Model predicted KCl and MgCl 2 sorption in membranes without adjustable parameters. [ABSTRACT FROM AUTHOR]

ABSTRACT: Membrane solution composition is one of the important factors that determine properties of ion‐exchange membranes. In this study, PVC‐based heterogeneous cation‐exchange membranes were prepared by the solution casting method. Effects of a hydrophilic additive [poly(ethylene glycol), PEG400] and degree of polymerization of poly(vinyl chloride) (PVC) on the morphology and electrochemical properties of the cation‐exchange membranes were investigated. The results revealed that the hydrophilic additive can improve membrane properties, including water uptake (Wu), ion‐exchange capacity (IEC), conductivity, and permselectivity. The improvements might be associated with an increase in accessibility of functional sites in the membrane matrix due to a higher hydrophilicity, indicated by a reduction of water contact angle and the greater void fraction shown by scanning electron microscopy. However, the permselectivity slightly decreased when the additive concentration was increased further. Meanwhile, increasing the degree of polymerization and PVC concentration resulted in higher permselectivity and lower conductivity, which might be due to a better resin distribution and a lower void fraction. Overall, the prepared membranes had relatively good conductivities (up to ∼2.5 mS/cm) and permselectivities (up to ∼0.92). In general the conductivity increased with increasing Wu and IEC, while the permselectivity showed the opposite trends. This could be associated with the efficacy of Donnan exclusion indicated by the IEC/Wu ratio and the Donnan equilibrium constant of the cation (K+). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46690. [ABSTRACT FROM AUTHOR]

Medical imaging performed in vivo captures geometries under Donnan osmotic loading, even when the articulating joint is otherwise mechanically unloaded. Hence patient-specific finite element (FE) models constructed from such medical images of cartilage represent osmotically induced prestretched/prestressed states. When applying classical modeling approaches to patient-specific simulations of cartilage a theoretical inconsistency arises: the in- vivo imaged geometry (used to construct the model) is not an unloaded, stress-free reference configuration. Furthermore when fitting nonlinear constitutive models that include osmotic swelling (to obtain material parameters), if one assumes that experimental data–generated from osmotically loaded cartilage–begin from a stress-free reference configuration the fitted stress-stretch relationship (parameters) obtained will actually describe a different behavior. In this study we: (1) establish a practical computational method to include osmotically induced prestretch/prestress in image-driven simulations of cartilage; and (2) investigate the influence of considering the prestretched/prestressed state both when fitting fiber-reinforced, biphasic constitutive models of cartilage that include osmotic swelling and when simulating cartilage responses. Our results highlight the importance of determining the prestretched/prestressed state within cartilage induced by osmotic loading in the imaged configuration prior to solving boundary value problems of interest. With our new constitutive model and modeling methods, we aim to improve the fidelity of FE-based, patient-specific biomechanical simulations of joints and cartilage. Improved simulations can provide medical researchers with new information often unavailable in a clinical setting, information that may contribute to better insight into the pathophysiology of cartilage diseases. [ABSTRACT FROM AUTHOR]

This article first outlines definitions and descriptions of key terms that will be used in the discussions that follow, including osmolarity, osmolality, osmotic and oncotic pressure. The physicochemical properties of water, ions and organic molecules are discussed in terms of their biological roles. Similarly, the interactions of amphipathic molecules and their three-dimensional structures in aqueous and non-aqueous environments are then explored. The movement of solutes and solvents across semipermeable membranes is considered and an assessment is made of the contribution of such mechanisms to normal physiology. Firstly, simple diffusion is described, followed by comparisons with facilitated diffusion and energy-dependent active transport focusing on the differences in kinetics and rate-limiting factors arising as a result. The mechanisms underlying Gibbs–Donnan equilibria are discussed, with particular emphasis as to how they arise across a selectively permeable membrane by way of a worked example. The equilibrium of forces influencing fluid movements across the capillary endothelium, known as Starling forces, is then described. Comparisons are made between the classic model as first proposed by Starling in 1896 and the modified glycocalyx model, which has developed over the past 25 years. Finally, the impact of these differences on our understanding of trans-capillary fluid flux is discussed. [ABSTRACT FROM AUTHOR]

Understanding ion transport through clays and clay membranes is important for many geochemical and environmental applications. Ion transport is affected by electrostatic forces exerted by charged clay surfaces. Anions are partly excluded from pore water near these surfaces, whereas cations are enriched. Such effects can be modeled by the Donnan approach. Here we introduce a new, comparatively simple way to represent Donnan equilibria in transport simulations. We include charged surfaces as immobile ions in the balance equation and calculate coupled transport of all components, including the immobile charges, with the Nernst-Planck equation. This results in an additional diffusion potential that influences ion transport, leading to Donnan ion distributions while maintaining local charge balance. The validity of our new approach was demonstrated by comparing Nernst-Planck simulations using the reactive transport code Flotran with analytical solutions available for simple Donnan systems. Attention has to be paid to the numerical evaluation of the electrochemical migration term in the Nernst-Planck equation to obtain correct results for asymmetric electrolytes. Sensitivity simulations demonstrate the influence of various Donnan model parameters on simulated anion accessible porosities. It is furthermore shown that the salt diffusion coefficient in a Donnan pore depends on local concentrations, in contrast to the aqueous salt diffusion coefficient. Our approach can be easily implemented into other transport codes. It is versatile and facilitates, for instance, assessing the implications of different activity models for the Donnan porosity. [ABSTRACT FROM AUTHOR]

Process development and characterization based on mathematic modeling provides several advantages and has been applied more frequently over the last few years. In this work, a Donnan equilibrium ion exchange (DIX) model is applied for modelling and simulation of ion exchange chromatography of a monoclonal antibody in linear chromatography. Four different cation exchange resin prototypes consisting of weak, strong and mixed ligands are characterized using pH and salt gradient elution experiments applying the extended DIX model. The modelling results are compared with the results using a classic stoichiometric displacement model. The Donnan equilibrium model is able to describe all four prototype resins while the stoichiometric displacement model fails for the weak and mixed weak/strong ligands. Finally, in silico chromatogram simulations of pH and pH/salt dual gradients are performed to verify the results and to show the consistency of the developed model. [ABSTRACT FROM AUTHOR]

An accurate prediction of ion selective adsorption in ion exchange membranes is essential to reflect the role of fixed charges on ion transport through the membrane in vanadium redox flow batteries (VRFB). Unlike those empirical models reported in the literature, this work reports on a new ion selective adsorption model with the Donnan effect considered for movable ions distributed in the membrane pores only. This model, no longer relying on empirical coefficients, is then applied to the calculation of ion transport through membranes in VRFBs. The model shows a more accurate prediction of vanadium crossover and membrane conductivity, and enables to capture the effect of key membrane properties on battery performance. It is found that (i) an increase in H 2 SO 4 concentration reduces the electrolyte imbalance and improves the coulombic efficiency; (ii) an increase in membrane porosity significantly improves the membrane effective conductivity; (iii) the change of fixed charges should be careful to balance all performances. Therefore, membrane properties and operating conditions need proper adjustment to improve the battery performance, and our VRFB model is a good tool to help membrane optimization. [ABSTRACT FROM AUTHOR]

Nanofiltration (NF) is widely used today for water purification, however, governing physical mechanisms are still largely unclear and predictive modeling remains a challenge, especially, for mixed ionic solutions. The current study systematically investigates NF of binary mixtures of NaCl and CaCl 2 with the purpose to understand the mechanisms and interplay between different ions in the membrane. Using extensive filtration data and the Nernst-Planck relations, the paper concludes that (a) the standard mean-field models based on an average Donnan potential are unsuitable for describing ion permeation in NF; (b) the observed ranking of ion permeabilities (Na + > Cl - > Ca 2+ ) points to the solvation (Born) energy rather than interaction with fixed charges as the main factor controlling ion permeation; (c) the fixed charges are largely neutralized by pairing with counter-ions, which reduces their role in ion permeation; (d) saturation of Ca 2+ uptake and its competition with Na + for pairing with fixed charges may explain the unusual decrease of Ca 2+ permeability with Ca 2+ concentration and its strong effect on Na + permeability. These conclusions, inconsistent with the commonly used mean-field picture, strongly suggest the need to revise the current approach to NF modeling. [ABSTRACT FROM AUTHOR]

Flow-electrode Capacitive Deionization (FCDI) is a membrane based electrically driven desalination method combining ion-exchange membranes and carbon based flow electrodes. The flow electrodes function as a pumpable ion storage and enable a fully continuous operation of FCDI. In contrast, classical capacitive deionization processes are operated in cycles. Yet another advantage of FCDI is the ability to treat high salinity water streams. Until now most FCDI related works are of experimental nature, a process model is needed to obtain a better understanding of the physical dependencies. We report a process model for continuous, steady state FCDI processes operated at constant voltage. Processes such as a continuous two-module FCDI process or processes based on a single FCDI desalination module operated in single-pass mode can be simulated. The storage of ions in the pores of the carbon particles is modeled using the modified Donnan model. Simulations performed with this model match experimental results well and were fitted using an apparent Stern capacity as the only fitting parameter. Influences of the module geometry and process parameters can be investigated, such as feed flow rates and flow electrode composition. The model predicts correctly a strong influence of the flow electrode flow rate on the desalination performance. [ABSTRACT FROM AUTHOR]

Free concentrations of Zn 2+ , Fe 3+ , Ca 2+ and Mg 2+ in a red wine (Raimat, Catalonia, Spain) have been determined, with the Donnan Membrane Technique (DMT) for the first time. The required equilibration time benefits from the acceptor solution including major cations. K + and Na + , mainly unbound to any ligand in the sample, have been identified as suitable reference ions. A free Zn concentration of 1.76 μmol L −1 determined with DMT was in excellent agreement with the free Zn concentration independently provided by the electroanalytical technique Absence of Gradients and Nernstian Equilibrium Stripping (AGNES), 1.7 μmol L −1 , amounting to 14.4% of the total Zn. The free concentrations found in this wine were 1.79 μmol L −1 Fe 3+ , 1.11 mmol L –1 Ca 2+ and 3.4 mmol L −1 Mg 2+ (8.82%, 40% and 57% of their total concentrations). Prior to the application of the techniques to the red wine, they had been cross-validated in Zn-tartrate solutions. [ABSTRACT FROM AUTHOR]

A Donnan Dialysis based process utilizing cation exchange membranes to separate and recover lithium, nickel, cobalt, and manganese during hydrometallurgical recycling of lithium ion battery cathodes is proposed. Compared to conventional processes, the process has the potential to achieve higher lithium recoveries and to recycle lixiviant. The present work introduces the process, develops mathematical equations to describe it, presents experimentally found cation mass transfer coefficients through cation exchange membranes, and uses the experimental data and equations to predict theoretical kinetics and recoveries achievable by the process. The simulation predicts that in two days, utilizing 5000 dm 2 of CMS C-1805 Neosepta monovalent CEM and 2000 dm 2 of CMX C-1586 Neosepta polyvalent CEM, the proposed process is capable of processing 1000 L of leachate containing 285 mol of lithium, 95 mol each of cobalt, nickel, and manganese. 94.1% of the lithium can be recovered as high purity lithium carbonate and 99.4% of the transition metals as mixed sulphates ready for solvent extraction. At a minimum 422.6 mol of pure sulphuric acid and 268 mol of potassium bicarbonate are needed. [ABSTRACT FROM AUTHOR]

In this study, the effects of the combination of acid hydrolysis and Donnan dialysis on the high-quality struvite production from digested sewage sludge were examined. The Box--Behnken design was applied in the hydrolysis using oxalic acid for the optimization of the conditions that affect the nutrients and metal release from digested sludge. An optimal condition was obtained at oxalic acid 0.5 M, acid/sludge ratio (mL/g) 10/1, and reaction time 60 min. The separation of the metals from hydrolyzed sludge liquid was carried out with the Donnan dialysis using a Nafion 117 cation exchange membrane. At the end of the 4 hours of operating time, the recovery values for Zn, K, Na, Mg, Fe, and Al were obtained as 67.9%, 62.1%, 57.6%, 39.4%, 5.3%, and 2.5%, respectively. The produced struvite meets the legal limits for fertilizer use in terms of Cd, Cu, Ni, Pb, Zn, Hg, and Cr content specified by Turkish regulations. A high Ca/Mg molar ratio and the presence of K, Na, and Al affected the efficiency of struvite crystallization. The use of oxalic acid resulted in low Ca release, and the metal ions that affect struvite purity were eliminated using Donnan dialysis. [ABSTRACT FROM AUTHOR]

In this study, a modified Donnan model (mDM) is incorporated into surface complexation model (SCM) to better understand the physicochemical processes for adsorption of hexavalent chromium, Cr(VI), on porous iron oxyhydroxide agglomerates (IOAs). The mDM includes a chemical potential term μ att to account for ionic transport and electrostatic interaction in micropores ( d mi < 2 nm) which is usually neglected in typical Donnan model (tDM). To estimate the parameters of mDM in a simple and accurate way, a rigorous protocol was presented. First, the prepared IOAs was characterized with a heteromorphous pore structure ( i.e. , co-existing micropores and macropores, d ma > 2 nm) demonstrating high Cr(VI) adsorption in a broad range of ionic strengths. The batch data was then fitted with Donnan model in PHREEQC to obtain Stern ( ψ S ) and Donnan ( ψ D ) potentials used for μ att calculation. The decreasing μ att values with ionic strength indicated obstructing effect of electrolyte ions on Cr(VI) uptake in micropores. Finally, the ionic activity coefficients and reaction constants were corrected using Pitzer model due to the high level electrolytes accumulated in the Donnan layer through osmotic and electrostatic attraction. Results of this study have captured the effects of inner structure of IOAs on Cr(VI) uptake and quantitatively discerned the contribution of micropores and macropores for adsorption reactions at different ionic strengths. [ABSTRACT FROM AUTHOR]

Ion adsorption and equilibrium between electrolyte and microstructure of porous electrodes are at the heart of capacitive deionization (CDI) research. Surface functional groups are among the factors which fundamentally affect adsorption characteristics of the material and hence CDI system performance in general. Current CDI-based models for surface charge are mainly based on a fixed (constant) charge density, and do not treat acid-base equilibria of electrode microstructure including so-called micropores. We here expand current models by coupling the modified Donnan (mD) model with weak electrolyte acid-base equilibria theory. In our model, surface charge density can vary based on equilibrium constants ( p K 's) of individual surface groups as well as micropore and electrolyte pH environments. In this initial paper, we consider this equilibrium in the absence of Faradaic reactions. The model shows the preferential adsorption of cations versus anions to surfaces with respectively acidic or basic surface functional groups. We introduce a new parameter we term “chemical charge efficiency” to quantify efficiency of salt removal due to surface functional groups. We validate our model using well controlled titration experiments for an activated carbon cloth (ACC), and quantify initial and final pH of solution after adding the ACC sample. We also leverage inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography (IC) to quantify the final background concentrations of individual ionic species. Our results show a very good agreement between experiments and model. The model is extendable to a wide variety of porous electrode systems and CDI systems with applied potential. [ABSTRACT FROM AUTHOR]

The dialysis method is classically used for drug separation before analysis, but does not provide direct and real-time drug quantification and has limitations affecting the dialysis rate. In this study, a phosphorus nuclear magnetic resonance ( 31 P-qNMR) method is developed for the real-time quantification of therapeutic molecules in vitro . The release kinetics of model drug, tenofovir (anti-HIV microbicide), was analyzed in vaginal fluid simulant (VFS), seminal fluid simulant (SFS), and human plasma (HP) from chitosan nanofibers (size ∼100-200 nm) using the NMR (direct) method and compared with dialysis/UV-Vis (indirect) method. The assay was linear in VFS/SFS (0.20-5.0 mM), HP (0.30-5.0 mM of drug concentration range) and specific no drug 31 P-qNMR chemical shift [∼15 ppm] interference with formulation/media components. Limit of detection values were 0.075/0.10/0.20 mM, whereas limit of quantification values were 0.20/0.20/0.30 mM in VFS/SFS/HP, respectively. The method was robust, precise (%RSE <2%), and accurate (%mean recovery 90%-110%). After 12 h, ∼77%/72%/70% wt/wt of tenofovir release was observed with direct, compared to ∼47%/52%/52% wt/wt by indirect method in VFS/SFS/HP, respectively. Approximately 20% decrease in %drug release observed with dialysis method suggested an interference with drug transport process due to the dialysis membrane and the Gibbs-Donnan effect. Overall, 31 P-qNMR provides more accurate, real-time, and direct drug quantification for effective in vitro–in vivo correlation. [ABSTRACT FROM AUTHOR]

Donnan theory and Goldman-Hodgkin-Katz equation (GHK eq.) state that the nonzero membrane potential is generated by the asymmetric ion distribution between two solutions separated by a semipermeable membrane and/or by the continuous ion transport across the semipermeable membrane. However, there have been a number of reports of the membrane potential generation behaviors in conflict with those theories. The authors of this paper performed the experimental and theoretical investigation of membrane potential and found that (1) Donnan theory is valid only when the macroscopic electroneutrality is sufficed and (2) Potential behavior across a certain type of membrane appears to be inexplicable on the concept of GHK eq. Consequently, the authors derived a conclusion that the existing theories have some limitations for predicting the membrane potential behavior and we need to find a theory to overcome those limitations. The authors suggest that the ion adsorption theory named Ling's adsorption theory, which attributes the membrane potential generation to the mobile ion adsorption onto the adsorption sites, could overcome those problems. [ABSTRACT FROM AUTHOR]

The contributions of the ionic transport through a cation-exchange membrane, with perfectly stirred bathing solutions, on the open circuit voltage and the membrane ohmic resistance under reverse electrodialysis conditions, have been theoretically investigated. The Nernst-Planck flux equations, together with the Donnan equilibrium relations and the electrical neutrality condition, are numerically solved by using the network simulation method. On the one hand, the voltage-current characteristic, the polarization curves and the contributions of the ion-exchange membrane to the open circuit voltage and the membrane resistance are studied in a single system with NaCl solutions. The results are compared to those analytically obtained by using linear variations of ionic concentrations inside the membrane. On the other hand, a similar study is done for a membrane immersed in solutions constituted by a mixture of NaCl and MgCl 2 . The uphill transport of the divalent cation against its concentration gradient is considered in the interpretation of the results. The numerical results are compared to those analytically obtained by considering the hypothesis of total co-ion exclusion inside the membrane. [ABSTRACT FROM AUTHOR]

The capillaries are the ‘business end’ of the circulatory system, where materials exchange between the plasma and tissues. Water-soluble molecules can diffuse through pores in the capillaries, and a Gibbs–Donnan equilibrium exists between the plasma and interstitium. There are several types of capillaries, which vary in their anatomical integrity and permeability. There is also a bulk flow of fluids between the plasma and interstitium, described by the Starling forces. Originally, these forces were thought to cause fluids to leave the capillaries at the arteriolar end and return at the venular end; the role of the lymphatics was to provide an ‘overflow’ mechanism due to protein leakage out of the capillaries. More recent work indicates that this concept needs modification. Lymph flow and interstitial colloidal osmotic pressure are now known to be greater than first thought, and the interstitium has a slightly negative hydrostatic pressure. It is now believed that filtration takes place along most of the capillary, and the lymphatic system plays a more important role in maintaining plasma–interstitium equilibrium and preventing oedema. The system acts as a ‘closed’ one in that the changes in fluid formation (e.g. following haemorrhage or cardiac failure) are self-limiting. However, in some circulations (e.g. those to the kidneys, glands and the gut), net fluid production or absorption is required. This requirement is fulfilled by an independence from the Starling forces, the systems behaving as ‘open’ ones. [ABSTRACT FROM AUTHOR]

The production of sugars from lignocellulosic biomass is the key to a sustainable, renewable chemical industry. Glucose, xylose and other monosaccharides can be easily produced by hydrolyzing cellulose and hemicellulose, the primary polysaccharides in biomass. However, the hydrolysis of biomass generates byproducts that, together with the mineral acid normally added in the hydrolysis step, have to be removed before the downstream conversion processes. In this work, the recovery of monosaccharides from lignocellulosic hydrolysates by means of Ion Exclusion Chromatography (IEC) has been studied. The analyzed process relies on new pretreatment and hydrolysis steps, involving the neutralization of the hydrolysate with sodium hydroxide. The adsorption behavior of the main components involved in the separation has been experimentally investigated. Pulse tests at the high loading encountered in preparative conditions have been performed for a selected group of model components found in the hydrolysates. For all the electrolytes, the retention volume fraction was always between the interparticle porosity and the total column porosity, confirming that ion exclusion was the dominant retention mechanism. On the other hand, sugars eluted before the total column porosity, indicating partial steric exclusion from the resin pores. This observation was then confirmed by size-exclusion experiments with polyethylene glycol standards, from which the distribution coefficient of the studied sugars has been determined. The comparison between the elution profiles of the same sugars in pure form and as a mixture present in the hydrolysate showed differences in both peak shape and retention times. Therefore, an investigation of the influence of the main electrolytes contained in the hydrolysates on sugars adsorption has been performed through the pulse on a plateau method. The electrolytes were found to enhance the sugars retention by promoting their adsorption onto the resin. However, this effect was not sufficient to explain the observed differences, which were effectively explained in terms of viscous fingering, due to the high viscosity differences between the eluent and the sample. A previously developed model for IEC has been updated to take into account all the observed phenomena and applied to simulate the experimental results. The proposed model was in good agreement with the batch-column elution profiles both for the pure components and for the actual hydrolysate, allowing a quantitative description of the separation. [ABSTRACT FROM AUTHOR]

Aiming at the application of PPy(polypyrrole) in the sensor, the sensing characteristics of the PPy mechanical sensor were studied. A method to measure the weak electric output signal of the sensor was presented under the condition of external static deflection applied, and the output signal measuring system was established with the function of shielding external disturbance. PPy sensor was applied by two sets of deflection displacements, the former values changed from small to large, the latter from large to small, then the corresponding sensor output signals were obtained in the shielding of external interference, by analyzing the relationship between the input deflection displacement and sensor output voltage, complete PPy sensor output characteristic curve equation of To-go and backhaul was gotten. The results indicate that the measurement system can achieve the output voltage signal of PPy mechanical sensor in the state of static deflection，and the sensor output keeps in line with the change of the input basically. Nonlinear hysteresis phenomena exists in the process of sensing according to the characteristic curve equation. The result provides a certain experimental basis and reference for the production of PPy mechanical sensor. [ABSTRACT FROM AUTHOR]

Wastewater generated from phosphoric acid industry poses a real environmental challenge. This water contains valuable components the utilization of which can contribute to the conservation of natural resources. Water sample from an effluent pond of a phosphoric acid plant was collected and characterized for its physical and chemical properties. The collected samples were subjected to a hybrid process of chemical precipitation followed by nanofiltration. Both sulphate and fluoride ions were separated by precipitation using Ca(OH) 2 . Silicon exhibited complex behaviour during the precipitation stage. The observed flux using the different tested membranes (NF90, NF270, and BW30) indicated the success of the pre-treatment method in preventing heavy fouling. Very high rejections were obtained using the NF90 and BW30 membranes and, generally, the rejection increased with pressure. As expected, higher flux and lower rejections were observed with NF270 for Si and H 3 PO 4 species. At a pressure of 20 bar the rejection increased with feed concentration which can be attributed to Donnan effects. It is concluded that NF270 could be potentially applied to separate PA from the rest of the species present in water. However, the main challenge is the low rejection of Si. [ABSTRACT FROM AUTHOR]

An approach for treating chemical equilibrium between compacted bentonite and aqueous solutions is presented. The treatment is based on conceptualizing bentonite as a homogeneous mixture of water and montmorillonite, and assumes Gibbs–Donnan membrane equilibrium across interfaces to external solutions. An equation for calculating the electrostatic potential difference between bentonite and external solution (Donnan potential) is derived and solved analytically for some simple systems. The solutions are furthermore analyzed in order to illuminate the general mechanisms of ion equilibrium and their relation to measurable quantities. A method is suggested for estimating interlayer activity coefficients based on the notion of an interlayer ionic strength. Using this method, several applications of the framework are presented, giving a set of quantitative predictions which may be relatively simply tested experimentally, e.g.: (1) the relative amount of anions entering the bentonite depends approximately on the square-root of the external concentration for a 1:2 salt (e.g. CaCl 2 ). For a 1:1 salt (e.g. NaCl) the dependence is approximately linear, and for a 1:2 salt (e.g. Na 2 SO 4 ) the dependence is approximately quadratic. (2) Bentonite contains substantially more nitrate as compared to chloride if equilibrated with the two salt solutions at equal external concentration. (3) Potassium bentonite generally contains more anions as compared to sodium bentonite if equilibrated at the same external concentration. (4) The anion concentration ratio in two bentonite samples of different cations (but with the same density and cation exchange capacity) resembles the ion exchange selectivity coefficient for that specific cation pair. The results show that an adequate treatment of chemical equilibrium between interlayers and bulk solutions are essential when modeling compacted bentonite, and that activity corrections generally are required for relevant ion equilibrium calculations. It is demonstrated that neglecting these aspects may lead to incorrect inferences regarding bentonite structure, and to incorrect interpretation of diffusion data. [ABSTRACT FROM AUTHOR]

A bond−graph model has been developed and applied to analyze the non−steady state transport kinetics of K + cations in the Donnan dialysis (DD) process. The model is based on a pseudo−thermodynamic network analysis and takes into account all the simultaneously occurring processes and phenomena, i.e. diffusion through aqueous layers, interfacial and membrane ion−exchange kinetics, interdiffusion of K + and H + cations, diffusion of a free electrolyte in the membrane, and the osmotic transport of water. Moreover, membrane morphology represented by its heterogeneity and non−uniform distribution of ionogenic groups has been included in the model. The numerical simulations of fluxes demonstrated that the DD efficiency in the investigated system results from osmotic water transport as well as an electrolyte solution sorption into the cation−exchange membrane. These phenomena cause dilution of the stripping phase and enable free diffusion of the electrolyte between the external solutions, respectively. The reverse K + ions flux from the stripping solution into the feed one observed in DD experiments results from the interdiffusion and non−exchange diffusion of the electrolyte. The numerical calculation results were compared with the experimental data measured for the DD systems operating with a low feed solution concentration (c f =0.01 M) and high stripping solution concentration (c s up to 1 M) resulting in observable osmotic flux of water. It was found that the developed model can be applied for the prediction of time−dependent concentration in the DD system. Consequently, the prediction of fluxes, concentration factors, recovery factors, etc. is also possible. The model calculations enable also the prediction of the experimental results as dependent on one of the main factors which influence DD efficiency, i.e. the stripping phase concentration. [ABSTRACT FROM AUTHOR]

Porous membranes with different charge on the surface and internal pore walls are prepared via the solvent-responsive layer-by-layer (SR-LBL) method. The effect of charge on the transport properties of different ions through the membranes is investigated in detail. The charge property of prepared membranes is tuned by assembling different charged polyelectrolytes (PEs) on the pore walls and the surface of the porous membranes. The results show that in a vanadium flow battery (VFB), the PE layers assembled on the surfaces (including pore walls) are capable to construct excellent ion transport channels to increase proton conductivity and to tune the ion selectivity via Donnan exclusion effect. Compared with the porous membrane with negative charges (7 bilayers), a VFB single cell assembled with a positively charged membrane (7.5 bilayers) yields a higher coulombic efficiency (98%). The water and ion transfer behavior exhibits a similar tendency. In the negative half-cell, the amount of V 3+ gradually increases as cycles proceed and the amount of V 2+ stays at a low and stable level. In the positive half-cell, the amount of VO 2+ decreases; while VO 2 + is accumulated. The imbalance of vanadium ions at both sides induces the discharge capacity fade. [ABSTRACT FROM AUTHOR]

Sorption of pure electrolytes and binary electrolyte mixtures in non-ionic microporous adsorbents was studied in batch and fixed-bed systems. Hypercrosslinked polystyrene (HCPS) and densely crosslinked dextran gel (G10) were used as adsorbents and the studied model systems were HCl/CaCl 2 /HCPS at 25 °C and Na 2 -tartrate/NaOH/G10 at 50 °C. The results were explained in terms of cooperative sorption and the experimental data were correlated using a generalized Donnan equilibrium model together with Pitzer model for evaluation of the ion-ion and ion-adsorbent interactions. Moreover, a model was included for partial ion dehydration at high concentrations. Non-linear sorption observed at very low and high concentrations of pure electrolytes was explained by electrostatic exclusion and partial ion dehydration. In binary mixtures, a more complex behavior was observed because of cooperativity and good separation of the electrolyte mixtures was obtained in the fixed-bed experiments involving pulse feed and elution with pure water. In the HCl/CaCl 2 /HCPS system, selective uptake of HCl was enhanced by increasing the total electrolyte concentration. This trend can be explained by taking into account both size exclusion of CaCl 2 and the non-ideal behavior of the electrolyte mixture. Separation of Na 2 -tartrate and NaOH was dominated by size exclusion of the tartrate anion and well-defined separation is possible even at very high column loading. Moreover, the observed splitting of Na 2 -tartrate to NaH-tartrate and NaOH can be explained on the basis of cooperativity. The results suggest that the proposed model applies equally well to materials having rigid microporous structure and to densely cross-linked gels. [ABSTRACT FROM AUTHOR]

A mathematical model of multicomponent ion transport through a cation-exchange membrane is developed based on the Nernst-Planck equation. A correlation for the non-linear potential gradient is derived from current density relation with fluxes. The boundary conditions are determined with the Donnan equilibrium at the membrane-solution interface, taking into account the convective flow. Effective diffusivities are used in the model based on the correlation of tortuosity and ionic diffusivities in free water. The model predicts the effect of an increase in current density on the ion concentrations inside the membrane. The model is fitted to the previously published experimental data. The effect of current density on the observed increase in voltage drop and the decrease in permselectivity has been analyzed using the available qualitative membrane swelling theories. The observed non-linear behavior of the membrane voltage drop versus current density can be explained by an increase in membrane pore diameter and an increase in the number of active pores. We show how the membrane pore diameter increases and dead-end pores open up when the current density is increased. Graphical Abstract: [ABSTRACT FROM AUTHOR]

It was demonstrated that a horse chestnut saponin, escin, stimulates the cell volume regulation system of thymocytes under hypoosmotic stress. However, this effect could be detected only at relatively low concentrations (1-5 μM), whereas at higher doses (10-100 μM) we observed multy-phase changes in the cellular volume and sustained swelling. [ABSTRACT FROM AUTHOR]