Model Of Ion Transport Research Articles

Modeling of hydrated cations transport through 2D MXene (Ti3C2Tx) membranes for water purification

Two-dimensional (2D) MXene membranes with high thermal and mechanical stability have shown great promise for water purification and desalination given their low energy consumption and high efficiency. In this work, we used a one-dimensional (1D) steady-state ion sieving and rejection model to describe the transport of hydrated cations through 2D lamellar MXene (Ti3C2Tx) membranes under transmembrane pressure field and external electric field. The model was validated using experimental data on the permeation fluxes of the 365 nm-thick MXene membrane with an interlayer spacing of 7.8 Å under transmembrane pressure of 0.2 atm at 298 K and under an external electric field between 0.1 and 8.25 V. The regressed model diffusion coefficients of penetrant (Di,pc) through the MXene membrane under transmembrane pressure field were 1.98 × 10−7 m2 h−1 for K+ and 1.77 × 10−7 m2 h−1 for Na+. Under the external electric field at 298 K and fixed starting solution concentration of 50 mg L−1 for K+ or Na+ cation, the diffusion coefficient of penetrant (Di,ec) from the regression were 2.55 × 10−9 m2 h−1 for K+ and 1.21 × 10−9 m2 h−1 for Na+. By applying the regressed parameters from both operation modes into the one-dimensional ion sieving and rejection models, the effects of interlayer spacing, potential voltage, temperature, and thickness on the permeation and rejection of hydrated K+ and Na+ cations through the MXene membrane can be effectively simulated. The use and modification of a theoretical model for ionic transport through 2D MXene (Ti2C3Tx) membranes we reported here can provide essential insights to guide future membrane design and determine its applicability of water desalination.

Targeted therapy for cystic fibrosis

The basic therapy of cystic fibrosis is currently aimed at slowing down the pathological processes associated with a decrease in the CFTR protein activity (cystic fibrosis transmembrane conductance regulator) in the gastrointestinal tract and the respiratory system. The pancreatic insufficiency is well compensated by replacement therapy with microsphere enzyme preparations and a high-calorie diet rich in proteins and fat. Chronic treatment of cystic fibrosis-related lung disease aims to improve the clearance of the bronchial tree, suppressing chronic bacterial infection and local chronic inflammation. However, no therapy was available to correct the defect in the gene or its product until 2012.The aim was to analyze literature on CFTR modulators, including their efficacy and safety, and assess the potential for developing new modulators to treat cystic fibrosis.Materials. The review included literature data (45 publications) on the use of CFTR modulators and international websites’ data.Results. Since the discovery of the CFTR gene in 1989, more than 2000 mutations or variants of the CFTR gene (hereinafter referred to as genetic variants) have been described. They interfere with the synthesis of the CFTR protein, its transport to the apical membrane of the cell, or disrupt its function as a channel for chloride anions. Although it is currently not possible to completely replace the mutant gene with a normal copy, small molecules have been identified that can modify the mutant CFTR protein and amend its function. The potential therapeutic measures are determined by class of the mutation. In clinical practice, pharmacological modeling of ion transport is currently possible only with the use of CFTR modulators: correctors and potentiators. The review defines these groups of drugs and describes 4 licensed CFTR modulators, including molecules of ivacaftor, lumacaftor, tezacaftor, elexacaftor. The data on the promising emerging next generation modulators and the prospects for the personalized selection of drugs using the assays on intestinal organoids are presented.

Analysis of Hemichannels and Gap Junctions: Application and Extension of the Passive Transmembrane Ion Transport Model.

Electrical synaptic transmission is an essential form of interneuronal communication which is mediated by gap junctions that permit ion flow. Three gene families (connexins, innexins, and pannexins) have evolved to form gap junctional channels. Each gap junctional channel is formed by the docking of the hemichannel of one cell with the corresponding hemichannel of an adjacent cell. To date, there has been a lack of study models to describe this structure in detail. In this study, we demonstrate that numerical simulations suggest that the passive transmembrane ion transport model, based on the generality of ion channels, also applies to hemichannels in non-junctional plasma membranes. On this basis, we established a gap junctional channel model, which describes hemichannels' docking. We simulated homotypic and heterotypic gap junctions formed by connexins, innexins, and pannexins. Based on the numerical results and our theoretical model, we discussed the physiology of hemichannels and gap junctions, including ion blockage of hemichannels, voltage gating of gap junctions, and asymmetry and delay of electrical synaptic transmission, for which the numerical simulations are first comprehensively realized.

Origin, growth, and characteristics of calcareous concretions in the varved sediments of a Glacial Lake

A comprehensive study is presented of the characteristics of calcareous concretions in the Connecticut Valley varved clay (CVVC), a glacial lake sediment, probed by an array of investigations, including compositional analyses via X-ray powder diffraction and energy-dispersive X-ray spectroscopy, mechanical property mapping by nanoindentation, selective dissolution, microstructure examination by optical and electron microscopy, and stable isotope analyses, with an objective to resolve some long-standing questions on their origin and growth mechanisms. Results show that these concretions are of a biogenic origin and consist of ~40 wt% primary host sediments and ~ 60 wt% secondary calcite post-depositionally precipitated as pore infills and inter-particle cement. The highly consistent layering and dry density between the carbonate-free host sediments in the concretions and in-situ varved sediments manifest that the precipitated calcite causes no disturbance to the original stratification and structure of the varved sediments. Moreover, both the mechanical properties (i.e., Young's modulus and hardness) and calcite concentration in concretions exhibit a radially decreasing pattern slightly disturbed by the sediments' layered textures. Further supported by the radial distribution patterns of stable carbon and oxygen isotopes, the CVVC concretions grow in a concentric pattern. A conceptual ion transport model is proposed to further interpret the growth mechanisms. These concretions grow radially in a nearly closed sediment system with diffusion-controlled transport of HCO3− from decaying organic matter and Ca2+ from porewater at direction-dependent rates dominated by the pore characteristics of the local host sediments. The diverse concretion morphologies are attributed to the different growth rates in different directions affected by the heterogeneous layering and pore sizes of the host sediments.

A 3D analytical ion transport model for ionic polymer metal composite actuators in large bending deformations

Ionic polymer metal composites (IPMCs) are a kind of soft electroactive polymer composites. An IPMC strip commonly has a thin polymer membrane coated with a noble metal as electrodes on both sides. Whenever an electric voltage is applied to the IPMC, it bends and whenever it is deformed, a low voltage is measurable between its electrodes, hence IPMC is an actuator as well as a sensor. They are well known for their promising features like low density, lightness, high toughness and remarkable stimulus strain, also, they have the potential for low-voltage operation while exhibiting acceptable large bending deformation. In this paper, a three-dimensional (3D), dynamic and physics-based model is presented analytically and experimentally for IPMC actuators. The model combines the ion transport dynamics within the IPMC and the bending dynamics of it as a beam under an electrical stimulation. In particular, we present an analytical model to create a relation between the input voltage and the output tip displacement of an IPMC actuator for large bending deformations. Experimental results show that the proposed model captures well the tip displacement.

Diffusion of chloride ion in coral aggregate seawater concrete under marine environment

In this study, the diffusion law of chloride ion in coral aggregate seawater concrete (CASC) (strength = C30) was investigated in order to determine the time-varying law of chloride ion migration and penetration in CASC under two different marine environments (i.e. immersion and wet/dry cycles). By measuring the free chloride ion concentration (Cf) and apparent chloride ion concentration (Cs) in CASC at different erosion times, erosion modes and erosion depths, the chloride ion diffusion coefficient (D) was determined, and then the chloride ion diffusion model of CASC was developed. Combined with COMSOL finite element simulation software, the chloride ion transport model was verified and improved. The results show that the diffusion law of chloride ions in the two environments conforms to Fick's second law of diffusion, and there was a significant promotional effect on the diffusion of chloride ions for the CASC in the wet/dry cycles environment; the trends of Cs and D are consistent with time and conform to the power function relationship. The value of Cf calculated by using COMSOL has good correlation with the test results; the curve shape of the numerical data is consistent with the test data, and numerical error is very small, which verifies the accuracy of the model developed in this study.

Design of Porous Carbons for Supercapacitor Applications for Different Organic Solvent-Electrolytes

The challenge of optimizing the pore size distribution of porous electrodes for different electrolytes is encountered in supercapacitors, lithium-ion capacitors and hybridized battery-supercapacitor devices. A volume-averaged continuum model of ion transport, taking into account the pore size distribution, is employed for the design of porous electrodes for electrochemical double-layer capacitors (EDLCs) in this study. After validation against experimental data, computer simulations investigate two types of porous electrodes, an activated carbon coating and an activated carbon fabric, and three electrolytes: 1.5 M TEABF4 in acetonitrile (AN), 1.5 M TEABF4 in propylene carbonate (PC), and 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 1:1 v/v. The design exercise concluded that it is important that the porous electrode has a large specific area in terms of micropores larger than the largest desolvated ion, to achieve high specific capacity, and a good proportion of mesopores larger than the largest solvated ion to ensure fast ion transport and accessibility of the micropores.

Modelling of heterogeneous ion transport in conducting polymer supercapacitors

The characteristics of conducting polymer supercapacitors are understood by modelling of heterogeneous ion transport within the electrodes.

Effect of non-isothermal flow on chloride ion transport in saturated concrete

The presence of a temperature difference changes the mode of motion of the fluid. The macroscopic motion of the fluid causes the relative displacement between the various parts of the fluid, which in turn affects the transfer of temperature in the medium. To investigate the effect of temperature transfer coupled fluid motion on chloride ion transport in concrete, a mesoscopic model of chloride ion transport in non-isothermal flow of concrete was established and compared with experimental data. Based on the finite element software, the influence of temperature transfer on the internal fluid motion and chloride ion transport of concrete was analyzed. And the effect of convective motion of fluid on the temperature transfer in concrete was studied. It is found that when the heating time is the same, the dynamic viscosity of the fluid in the concrete decreases with the increase of temperature; the chloride ion concentration increases with the increase of temperature at the same depth of concrete; when considering the influence of laminar flow, the temperature is transmitted faster in the concrete and exhibits uneven diffusion from high temperature to low temperature; non-isothermal flow promotes the diffusion of chloride ions in concrete, and the higher the temperature.

Flow effects on the surface properties of surfactant foam films.

The surface electrostatic properties of liquid foam, involving the electrokinetic (EK) phenomena in the liquid-gas interface, have significant effects on the stability of the foam. Here, we established a theoretical model for ion transport in liquid films by combining the liquid flow and surface reaction. We found that the surface electrostatic properties of liquid foams were influenced unexpectedly by the pressure-induced flow. The liquid flow will induce the potential and concentration differences in the flow direction. When the pressure drop increases to a certain high value, the induced potential and salt concentration difference increases, leading to the change of the surface electrostatic properties such as zeta potential and the surface charge density. This change shows that the surface electrostatic properties of foam films depend on the coupling of various factors including ion distribution and pressure drop, which deepens our understanding of the electrostatic properties of the foam films.

Tunable Nanopore Arrays as the Basis for Ionic Circuits.

There has been considerable interest in preparing ionic circuits capable of manipulating ionic and molecular transport in a solution. This direction of research is inspired by biological systems where multiple pores with different functionalities embedded in a cell membrane transmit external signals and underlie all physiological processes. In this manuscript, we describe the modeling of ion transport through small arrays of nanopores consisting of 3, 6, and 9 nanopores and an integrated gate electrode placed on the membrane surface next to one pore opening. We show that by tuning the gate voltage and strategically placing nanopores with nonlinear current-voltage characteristics, the local signal at the gate affects ionic transport through all nanopores in the array. Conditions were identified when the same gate voltage induced opposite rectification properties of neighboring nanopores. We also demonstrate that an ionic diode embedded in a nanopore array can modulate transport properties of neighboring pores even without a gate voltage. The results are explained by the role of concentration polarization and overlapping depletion zones on one side of the membrane. The modeling presented here is intended to become an inspiration to future experiments to create nanopore arrays that can transduce signals in space and time.

Theoretical Analysis of the Stationary Transport of 1:1 Salt Ions in a Cross-Section of a Desalination Channel, Taking into Account the Non-Catalytic Dissociation/Recombination Reaction of Water Molecules.

In electromembrane systems, the theoretical study of salt ion transport usually uses mathematical models of salt ion transport in the depleted diffusion layer of ion-exchange membranes. This study uses a one-dimensional mathematical model of salt ion transport in a cross-section of a desalination channel formed by anion-exchange and cation-exchange membranes, taking into account an effect of a dissociation/recombination reaction of water molecules. The reaction on the one hand leads to an overlimiting mass transfer due to the effect of exaltation of the limiting current. On the other hand, an appearance of new electric charge carriers (hydrogen and hydroxyl ions) can reduce the space charge that occurs in membranes and suppress an electroconvective mechanism of overlimiting transport. Thus, there is a problem of studying these phenomena together, taking into account their mutual influence, and this article is devoted to the solution of this problem. Theoretically, using a method of mathematical modeling and numerical research, main regularities are established; in particular, it is shown that the dissociation/recombination reaction of water molecules does not lead to the destruction of the double electric layer at the membranes, but also creates a new double electric layer in the middle of the desalination channel. Thus, the space charge and the dissociation/recombination reaction significantly affect each other and simultaneously the transport of salt ions.

Pore-scale investigation on ion transport and transfer resistance in charged porous media with micro-macro structure

Capacitive deionization is an electrochemical desalination technology, in which ions are removed from aqueous solution using porous carbon electrodes. Poisson-Nernst-Planck equations are fully solved by the lattice Boltzmann method to investigate the dynamic ion transport and adsorption processes from macropores between carbon particles into micropores inside carbon particles. Effects of potential, ion concentration and thickness of the microporous zone on the dynamic ion transport processes are investigated. Pore-scale results show that the ion transport first occurs at the micropore/macropore interface and then extends to the inner part of the microporous zone. Adsorption of Na+ ion consumes more time to reach the equilibrium state compared with expulsion of Cl− ion, and the ion concentrations of microporous zones in the steady state predicted by simulations agree well with the results obtained by the Donnan model. The kinetic rate parameters of the finite-rate ion transport model are obtained using data fitting based on the individual ion transfer fluxes into micropores calculated by the pore-scale simulation. It is found that identified kinetic rate parameters are constant showing the validity of the model, and the thickness of the microporous zone has a great influence on the values.

A one-dimensional model for ion transport in a flame with two absorbing surfaces

This paper presents numerical and asymptotic analytical solutions for the current–voltage characteristic of a flame using a one-dimensional ion transport model with boundary conditions that include detailed treatment of sheath formation. Non-dimensional conservation equations are presented for the free electron, the hydronium ion, and the electrical potential in a one-dimensional flow field with uniform velocity, electrical mobility, and diffusivity, but allowances are made for non-equilibrium electron temperature. In this study, the size and location of the ion formation region and the electric Reynolds numbers are changed, and their impacts are studied. The model predicts the formation of charged sheaths at both ends of the domain, which are responsible for saturation events that are reliably observed in experiments. A new saturation regime can be made to appear in the model, but its absence from the experiment is argued to have implications on transport near absorbing surfaces in the experiment. For example, the Reynolds numbers at which the current–voltage characteristic converges to the shape and magnitude observed in the experiment implies that the sheaths form in the low-velocity region in the real flow that reduces the apparent Reynolds number.

Transient analysis of the nonmonotonic response of counterflow laminar diffusion flames in alternating current and step electric fields using a one-dimensional ionic transport model.

The electrohydrodynamic response of a counterflow laminar diffusion flame to applied alternating current (ac) electric fields is investigated experimentally and numerically. The flame positions are observed to show typical response to applied ac electric fields with high and moderate frequencies. The flame position does not respond above a threshold frequency corresponding to a certain collision response time, below which it oscillates in phase with the applied electric field. At a very low frequency (less than approximately 1 Hz), however, the flame position is observed to vary nonmonotonically as a function of time. To elucidate the nonmonotonic behaviors, a one-dimensional ionic transport model was employed by applying time-dependent electric fields. The responses of flame positions for ionized layers substituting for counterflow diffusion flames were systematically investigated with respect to one-way ionic wind (OIW) and two-way ionic wind (TIW) models. Consequently, it is demonstrated that the ionic models can produce not only harmonic flame oscillations for relatively low ac frequencies, but also free flame oscillations for stepwise voltages, which originated from the interaction between electrostatic force and ionic wind-induced force in the ionic system for both the OIW and TIW models.

Kinetic modelling of parallel ion transport in the scrape-off layer and divertor of inter-edge localised mode JET high radiative H-mode plasma

KInetic code for Plasma Periphery (KIPP) was used to assess the importance of kinetic effects of parallel ion transport in the scrape-off layer (SOL) and divertor of JET high radiative H-mode inter-edge localised mode plasma conditions with strong nitrogen (N2) injection, leading to partial detachment at divertor targets. Plasma parameter profiles along the magnetic field from one of the EDGE2D-EIRENE simulation cases were used as an input for KIPP runs. The profiles were maintained by particle and power sources. This work is a continuation of the previous study carried out for electrons (Chankin et al 2018 Plasma Phys. Control. Fusion 60 115011).In this modelling KIPP calculated ion distribution functions and ion parallel power fluxes. In the main SOL kinetic effects lead to a reduction of heat (conductive power) fluxes compared to Braginskii fluxes by factors 3−4 (‘heat flux limiting’). In the divertor, on the contrary, a strong ‘heat flux enhancement’, by up to two orders of magnitude above Braginskii’s, was found. Similar to cases for electrons, high ion heat flux enhancement factors, in particular near targets, are attributed to a non-local transport of super-thermal ions originating from positions along field lines with the highest ion temperature, resulting in the appearance of bump-on-tail features on ion heat flux density profiles. Despite ion heat flux enhancement factors at the target being much higher than for electrons, total power fluxes, ion plus electron, were dominated by ion and electron convection and electron conduction, with ion conductive fluxes playing a secondary role. This must be attributed to lower ion (than electron) velocities (factor ∼ reduction), which are not compensated by kinetic effects of lower ion upstream collisionality.

Electrosorption mechanism and nonequilibrium thermodynamics model of room-temperature ionic liquids within graphene nanochannels

<p indent=0mm>Supercapacitor, an advanced energy-storage technique based on ion electrostatic adsorption at the solid–liquid interface, exhibits fast charge–discharge rates, high power density, high rate ability, and long cycle life. Two-dimensional nanomaterials (e.g., graphene) and room-temperature ionic liquids (RTILs) have been considered potential electrode and electrolyte candidates, respectively, for supercapacitors. However, their high concentration, nanosized confined space, and complex molecular structure/intermolecular interactions make the ion packing structure and electrosorption process substantially different from that in conventional dilute electrolytes (e.g., aqueous solution and organic electrolyte) near the nonconfined space, which cannot be interpreted by the Gouy–Chapman–Stern model and Debye–Huckel approximation based on the continuous medium hypothesis. In this study, molecular dynamics simulations are employed to comprehensively explore the in-depth mechanisms of ion distribution at equilibrium and ion transport at nonequilibrium within the multilayer graphene nanochannel/RTILs system. The ion layer structure and its number density inside the graphene nanochannels are significantly enhanced compared with the nonconfined graphene plane. Moreover, the position of counter-ion within the graphene nanochannel is much closer to the charged wall, indicating better charge-storage capability. These phenomena are mainly attributed to the more prominent interactions between graphene and ions inside the confined space. In addition, the ion transport behaviors inside the graphene nanochannel are strongly dependent on the electrode potential and channel widths. In particular, an anion adsorption-dominated charging mechanism is recognized on the graphene plane, whereas confined graphene nanochannels exhibit more complex ion transport behaviors, i.e., the anion adsorption-dominated and cation desorption-dominated behaviors alternate with increasing potential. The ion transport mechanism is highly related to the confinement, potential, ion–ion interaction, and ion–electrode interaction. Finally, an interfacial ion transport model based on nonequilibrium thermodynamics theory is proposed to analyze the real-time flux of anions and cations within the electrodes in the nonequilibrium state. It is found that the decreased charge storage at high charge–discharge rates is mainly attributed to the significant hindrance of co-ion transport, which is quite different from the traditional view (i.e., the hindrance/hysteresis of counter-ion adsorption). Such a phenomenon can be interpreted as follows. First, the transient formation of crowded counter-ions and dilute co-ions inside the graphene nanochannel leads to slower transport of the co-ions. Second, the decreasing number density of co-ions inside the graphene nanochannel also hinders the flux of co-ions in and out of the electrode. These insights reveal the energy and mass transfer mechanisms during the electrostatic adsorption process within complex graphene nanochannel/RTILs systems, which can potentially guide the design and fabrication of electrode materials and electrolytes for high-performance supercapacitors.

Investigation of Radiation Effects on FD-SOI Hall Sensors by TCAD Simulations.

This work investigates the responses of the fully-depleted silicon-on-insulator (FD-SOI) Hall sensors to the three main types of irradiation ionization effects, including the total ionizing dose (TID), transient dose rate (TDR), and single event transient (SET) effects. Via 3D technology computer aided design (TCAD) simulations with insulator fixed charge, radiation, heavy ion, and galvanomagnetic transport models, the performances of the transient current, Hall voltage, sensitivity, efficiency, and offset voltage have been evaluated. For the TID effect, the Hall voltage and sensitivity of the sensor increase after irradiation, while the efficiency and offset voltage decrease. As for TDR and SET effects, when the energy deposited on the sensor during a nuclear explosion or heavy ion injection is small, the transient Hall voltage of the off-state sensor first decreases and then returns to the initial value. However, if the energy deposition is large, the transient Hall voltage first decreases, then increases to a peak value and decreases to a fixed value. The physical mechanisms that produce different trends in the transient Hall voltage have been analyzed in detail.

A Comprehensive Biophysical Model of Ion and Water Transport in Plant Roots. III. Quantifying the Energy Costs of Ion Transport in Salt-Stressed Roots of Arabidopsis.

Salt stress defense mechanisms in plant roots, such as active Na+ efflux and storage, require energy in the form of ATP. Understanding the energy required for these transport mechanisms is an important step toward achieving an understanding of salt tolerance. However, accurate measurements of the fluxes required to estimate these energy costs are difficult to achieve by experimental means. As a result, the magnitude of the energy costs of ion transport in salt-stressed roots relative to the available energy is unclear, as are the relative contributions of different defense mechanisms to the total cost. We used mathematical modeling to address three key questions about the energy costs of ion transport in salt-stressed Arabidopsis roots: are the energy requirements calculated on the basis of flux data feasible; which transport steps are the main contributors to the total energy costs; and which transport processes could be altered to minimize the total energy costs? Using our biophysical model of ion and water transport we calculated the energy expended in the trans-plasma membrane and trans-tonoplast transport of Na+, K+, Cl−, and H+ in different regions of a salt-stressed model Arabidopsis root. Our calculated energy costs exceeded experimental estimates of the energy supplied by root respiration for high external NaCl concentrations. We found that Na+ exclusion from, and Cl− uptake into, the outer root were the major contributors to the total energy expended. Reducing the leakage of Na+ and the active uptake of Cl− across outer root plasma membranes would lower energy costs while enhancing exclusion of these ions. The high energy cost of ion transport in roots demonstrates that the energetic consequences of altering ion transport processes should be considered when attempting to improve salt tolerance.

Low-Frequency Impedance-Based Cell Discrimination Considering Ion Transport Model in Cell Suspension.

Low-frequency impedance-based (LFI) cell discrimination as a novel non-destructive and non-invasive cell discrimination is proposed. LFI cell discrimination discriminates the cell type by considering an ion transport model in cell suspension. Ion transport model in cell suspension is constructed on the basis of Fick's laws of diffusion in the extracellular region under ion permeability P which represents the characteristics of cell type. P is achieved using the ion transport model equation through an iterative curve fitting to an ion concentration in extracellular region obtained from low-frequency impedance which is assumed to be linearly related to the ion concentration in extracellular region. In experiment, the electrical impedance spectra from the frequency of 200kHz to 2.0MHz are measured over time during producing ions from intracellular region to extracellular one in cell suspension using an impedance analyzer and an interdigitated array electrode system. As a target cell type, two different cell types based on Medical Research Council 5 (MRC-5), which are different in intracellular component are used. The curve fitting is performed for the low-frequency impedance at 200kHz at which impedance reflects the ion concentration in extracellular region in order to obtain P of each cell type. As a result, each cell type has its own P. The proposed LFI cell discrimination successfully discriminates the cell type.