Transport Of Ionic Species Research Articles

A nonlinear phase-field model of corrosion with charging kinetics of electric double layer

Abstract A nonlinear phase-field model is developed to simulate corrosion damage. The motion of the electrode-electrolyte interface follows the usual kinetic rate theory for chemical reactions based on the Butler-Volmer equation. The model links the surface polarization variation associated with the charging kinetics of an electric double layer (EDL) to the mesoscale transport. The effects of the EDL are integrated as a boundary condition on the solution potential equation. The boundary condition controls the magnitude of the solution potential at the electrode$-$electrolyte interface. The ion concentration field outside the EDL is obtained by solving the electro$-$diffusion equation and Ohm's law for the solution potential. The model is validated against the classic benchmark pencil electrode test. The framework developed reproduces experimental measurements of both pit kinetics and transient current density response. The model enables more accurate information on corrosion damage, current density, and environmental response in terms of the distribution of electric potential and charged species. The sensitivity analysis for different properties of the EDL is performed to investigate their role in the electrochemical response of the system. Simulation results show that the properties of the EDL significantly influence the transport of ionic species in the electrolyte.

Light-Driven Ionic and Molecular Transport through Atomically Thin Single Nanopores in MoS2/WS2 Heterobilayers.

Nanofluidic ionic and molecular transport through atomically thin nanopore membranes attracts broad research interest from both scientific and industrial communities for environmental, healthcare, and energy-related technologies. To mimic the biological ion pumping functions, recently, light-induced and quantum effect-facilitated charge separation in heterogeneous 2D-material assemblies is proposed as the fourth type of driving force to achieve active and noninvasive transport of ionic species through synthetic membrane materials. However, to date, engineering versatile van der Waals heterostructures into 2D nanopore membranes remains largely unexplored. Herein, we fabricate single nanopores in heterobilayer transition metal dichalcogenide membranes with helium ion beam irradiation and demonstrate the light-driven ionic transport and molecular translocation phenomena through the atomically thin nanopores. Experimental and simulation results further elucidate the driving mechanism as the photoinduced near-pore electric potential difference due to type II band alignment of the semiconducting WS2 and MoS2 monolayers. The strength of the photoinduced localized electric field near the pore region can be approximately 1.5 times stronger than that of its counterpart under the conventional voltage-driven mode. Consequently, the light-driven mode offers better spatial resolution for single-molecule detection. Light-driven ionic and molecular transport through nanopores in van der Waals heterojunction membranes anticipates transformative working principles for next-generation biomolecular sequencing and gives rise to fascinating opportunities for light-to-chemical energy harvesting nanosystems.

Phase field study of pitting corrosion: Electrochemical reactions and temperature dependence

This study presents a new phase field model of pitting corrosion for metal materials, encapsulating the transport of ionic species and electrochemical reactions in the electrolyte, and the effect of temperature on corrosion kinetics is incorporated by relating the interface kinetics parameter to the temperature. The Allen-Cahn and Cahn-Hilliard equations, along with the Poisson’s equation, is established to govern phase transformation, ions diffusion and electrostatic potential distribution, respectively. The model is validated by conducting several benchmark numerical studies. Simulation results demonstrate that within the temperature range of 10 °C to 20 °C, the model closely matches experimental data and result from sharp interface model. Additionally, the model effectively reproduces the pit shapes observed in experiments and captures variations in ion concentrations within the electrolyte. Several examples of the model simulating corrosion problems with complex evolving morphologies are provided.

A Transparent Poly(vinyl alcohol) Ion-Conducting Organohydrogel for Skin-Based Strain-Sensing Applications.

The increasing demand for cost-efficient and user-friendly wearable electronic devices has led to the development of stretchable electronics that are both cost-effective and capable of maintaining sustained adhesion and electrical performance under duress. This study reports on a novel physically crosslinked poly(vinyl alcohol) (PVA)-based hydrogel that serves as a transparent, strain-sensing skin adhesive for motion monitoring. By incorporating Zn2+ into the ice-templated PVA gel, a densified amorphous structure is observed through optical and scanning electron microscopy, and it is found that the material can stretch up to 800% strain according to tensile tests. Fabrication in a binary glycerol:water solvent results in electrical resistance in the kΩ range, a gauge factor of 0.84, and ionic conductivity on the scale of 10-4 S cm-1 , making it a potentially low-cost candidate for a stretchable electronic material. This study characterizes the relationship between improved electrical performance and polymer-polymer interactions through spectroscopic techniques, which play a role in the transport of ionic species through the material.

Impact of pH-Regulated Wall Charge on the Modulation of Electroosmotic Flow and Transport of Ionic Species through Slit Nanochannels

Impact of pH-Regulated Wall Charge on the Modulation of Electroosmotic Flow and Transport of Ionic Species through Slit Nanochannels

Optimization of electroosmotic flow to enhance the removal of contaminants from low‑permeable soils

Electrokinetic is an effective method for the extraction of contaminants from low-permeable soils. This work examines the influence of Ca+2 ions on the electroosmotic flow and the effect of electric potential, current, and pH variations on the removal of Pb2+, Na+, and Clˉ ions from artificially contaminated soil during vertical electrokinetic experiments. The DC electric field of 1 Vcm−1 was applied across the soil specimen via steel mesh electrodes for 24, 48, and 72 h of the experiment. In this work, the vertical electrokinetic cell was used to avoid the deposition of Na+ and Pb +2 ions near the soil surface after the treatment. making it even less permeable. The results show that the formation of acidic and alkaline environments in soil specimens affects the transport of ionic species by reducing the effect of electromigration and electroosmotic water flow. The enhancement of electroosmosis using Ca+2 ions as an electrolyte increased the extraction efficiency of Pb2+ (i.e., 41%) and Na+ (i.e., 82%) ions instead of the Clˉ (i.e., 69%) ions due to the high electroosmotic flow (i.e., 81 mL) from anode to the cathode. For relatively low electroosmotic flow (i.e., 19 mL), the extraction efficiency of Clˉ ions (i.e., 76%) was higher than that of Pb2+ (i.e., 27%) and Na+ (i.e., 44%) ions. The results demonstrated that the extraction efficiency of ions and energy consumption increased with treatment time and were higher during the first 24 h of the experiments.Graphical Abstract

Transport of ionic species affected by interactions with a pH-sensitive monolayer of microgel particles attached to electrode surface

In this work, we present the use of pH-sensitive microgel based on acrylic acid crosslinked with N,N′-bis(acryloyl)cystamine in the modification of Au electrode surface through the chemisorption process. The strong interactions between the crosslinker disulfide bridges and the gold surface were employed. The shape and morphology of the microgel particles were determined using scanning electron microscopy (SEM). The gel sensitivity to pH was examined using the dynamic light scattering technique (DLS). The impact of pH on electrode processes at the modified Au surface was studied using cyclic voltammetry (CV). It was found that at appropriate pH the microgel particles formed a loose monolayer on the electrode surface, which, in the swollen state, was able to block the transport of negatively charged redox probe to the electrode surface. On the other hand, when the microgels were in the shrunken state, the electrode surface was partially uncovered, and that allowed the redox probe to reach the electrode surface. The anchoring process of the microgels on the Au electrode surface was monitored with a quartz crystal microbalance with dissipation technique (QCM-D). The electrochemical properties of the modified with the pH-sensitive microgel layer electrodes were examined in the presence of either positively or negatively charged redox probes using CV and electrochemical impedance spectroscopy (EIS). It turned out that the electrochemical signals were strongly affected by both: degree of swelling of the microgel and protonation of the carboxylic groups of acrylic acid in the polymer network. The switching of electrode behavior was fully reversible and relatively fast.

Effect of Dielectric Saturation on Ion Activity Coefficients in Ion Exchange Membranes.

Polymeric ion exchange membranes are used in water purification processes to separate ions from water. The distribution and transport of ionic species through these membranes depend on a variety of factors, including membrane charge density, morphology, chemical structure, and the specific ionic species present in the fluid. The electrical potential distribution between membranes and solutions is typically described using models based on Donnan theory. An extension of the original theory is proposed to account for the nonideal behavior of ions both in the fluid and in the membrane as well to provide a more robust description of interactions of solutes with fixed charge groups on the polymer backbone. In this study, the variation in dielectric permittivity in the membrane medium with electric field strength is taken into account in a model based on Gouy–Chapman double-layer theory to provide a more accurate description of ion activity coefficients in an ion exchange membrane. A semianalytical model is presented that accounts for the variation in dielectric permittivity of water in a charged polymer membrane. A comparison of this model with Manning’s counterion condensation model clearly demonstrates that by incorporating changes in water dielectric permittivity with electric field strength, much better agreement with experiments can be obtained over a range of salt concentrations for different ions.

(Keynote) Selective Transport of Ionic Species in Membranes - Effects of Specific Interactions and Nano-Morphology

Selective transport of specific ions is not only key to certain chemical and electrochemical applications, it also raises a number of interesting fundamental questions. For example, in a redox-flow battery, a membrane has to efficiently separate the electrochemically active ionic species (e.g. the different vanadium species present in anolyte and catholyte of a VRFB) while conducting other ionic species for mediating the electrochemical reactions. Fundamentally, selective transport is related to issues of ion uptake and ion mobility. There may be preferred uptake of certain ionic species while others may dominate ionic transport; under certain conditions, an anion exchange membrane (AEM) may even turn into a proton conductor.This presentation provides insight into the effects membrane morphology and chemical interactions have on selective ion transport. Common thermodynamic considerations have been modified by including effects of ion solvation and the influence acid/base properties of the fixed ions have on counter-ion condensation. In addition, insights into the membrane’s nano-morphology allowed to identify sterical effects on ionic transport (ion-sieving).With these sophistications, transport data are described in a quantitative way and guidelines are provided which may help to select or tailor membranes for particular applications requiring selective ion transport.

Impact of aqueous solution pH on network structure of corrosion‐induced surface layers of boroaluminosilicate glass

AbstractUnderstanding of the long‐term stability of vitrified nuclear waste glass is critical to its safe storage, but knowledge gaps remain regarding the corrosion mechanism, especially with respect to surface alteration layers whose presence changes the observed corrosion rates. Here, we report the aqueous corrosion of a model boroaluminosilicate glass at ground water relevant pHs as investigated by vibrational spectroscopy to understand the network structure of the alteration layer that we hypothesize controls the corrosion rates. Both specular reflection infrared spectroscopy and infrared variable angle spectroscopic ellipsometry were used to elucidate details of the structure of the alteration layers formed at pH 7 and pH 9. After 2312 days, the thickness of the alteration layer is found to be ∼2000 nm for corrosion at pH 7 and ∼300 nm for corrosion at pH 9. The interpretation of the vibrational spectra suggests that alteration layers formed at pH 7 and pH 9 both exhibit a porous network with "silica‐like" structures, but with differences in the bond lengths and bond angles in the glass network. Moreover, the relative abundance of the hydrous species within the porous network appears to be dependent on pH. Additionally, the spectroscopic data suggest that the B and Ca trapped in the alteration layer during the secondary corrosion of the pH 9 pre‐corroded sample in pH 3 solution are hydrated within the nano‐porous layer and not bound to the silicate network. However, the precise chemical form remains to be determined. Based on these findings, we propose that the combination of the network structure of the alteration layer and the relative abundance of hydrous species within the alteration layer act to control the transport of ionic species dissolved from the reaction front to the aqueous solution outside the glass.

Chemical and mechanical interfacial degradation in bifacial glass/glass and glass/transparent backsheet photovoltaic modules.

Glass/glass (G/G) photovoltaic modules are quickly rising in popularity, but the durability of modern G/G packaging has not yet been established. In this work, we examine the interfacial degradation modes in G/G and glass/transparent backsheet modules under damp heat (DH) with and without system bias voltage, comparing emerging polyolefin elastomer (POE) and industry-standard poly(ethylene-co-vinyl acetate) (EVA) encapsulants. We investigate the transport of ionic species at cell/encapsulant interfaces, demonstrating that POE limits both sodium and silver ion migration compared with EVA. Changes to the chemical structures of the encapsulants at the cell/encapsulant interfaces demonstrate that both POE and EVA are more susceptible to degradation in modules with a transparent backsheet than in the G/G configuration. Adhesion testing reveals that POE and EVA have comparable critical debond energies after the DH exposures regardless of system bias polarity. The results of this study indicate that the interfacial degradation mechanisms of G/G appear to be similar to those of conventional glass/backsheet modules. For emerging materials, our results demonstrate that POE offers advantages over EVA but that transparent backsheets may accelerate encapsulant degradation due to increased moisture ingress when compared with the G/G structure.

Electroosmotic transport and current rectification of viscoelastic electrolyte in a conical pore nanomembrane

Nanomembranes have received a wide range of applications in water treatment, gas separation, molecular and supramolecular separations. Nanopores offer the separation of the components even at nano- or picomolar concentrations. In addition, DNA translocation, DNA sequencing of nucleotides, single molecular analyses for biomedical nanoscopic devices are perhaps the unique feature of nanomembranes that convectional membranes may not achieve. Despite such an overwhelming application, the theoretical understanding of electroosmotic transport in nanopores is still in infancy and it is limited to simple Newtonian-like fluids. This work has numerically investigated the ionic current rectification (ICR) in a conical nanopore filled with viscoelastic electrolyte. ICR quantifies the unequal upstream and downstream ionic flow rates during the forward and reverse potential bias. This is similar to a semiconductor transistor’s current potential (I−V) response. The ICR exhibits several potential applications in the design of biosensors for the measurement and analysis of biofluids such as blood, lymph, and plasma, micro-scale pumping devices, ion-selective membranes, etc. The electroosmotic flow (EOF) in the conical nanopore of Carreau fluid is investigated by solving a set of Poisson, Nernst–Planck, and momentum equations to account for the electric potential, transport of ionic species, and velocity field. The behaviors of ICR in Carreau fluid are examined by varying the shear-thinning index (0.6≤n≤1), Debye length (1≤κRt≤50), Deborah number (1≤De≤100), and applied electric potential (−50≤V≤50). The electroosmotic flow is observed to be significantly stronger in shear-thinning fluids. All else being equal, the volumetric flow rate increases several folds in shear-thinning fluids. Shear-thinning fluid behavior enhances the magnitude of the current in the conical nanopore.

New insights into the definition of membrane cleaning strategies to diminish the fouling impact in ion exchange membrane separation processes

Ion exchange membranes represent the main core of a number of separation processes such as electrodialysis, diffusion dialysis and Donnan dialysis, among others, at which the key role of these membranes is to control the transport of ionic species and their selective separation simultaneously. However, the ion exchange capacity, selective separation, stability and durability of ion exchange membranes in separation processes are especially limited under the use of natural feedwaters due to their heterogeneous and multivalent ionic composition, which leads to several fouling issues. This effect provokes a clear undesirable evolution with time in the initial membrane properties and characteristics, thus significantly decreasing the overall process performance in several applications. As a consequence, not only a further understanding of the fouling mechanisms and the interactions between foulant(s) and membrane(s) is crucial, but also development of adequate membrane cleaning protocols to alleviate the fouling impact after prolonged operations. Therefore, the aim of the present review is to define efficient membrane cleaning strategies to control and mitigate the impacts of fouling phenomena on ion exchange membranes in separation processes, paying special attention to the type of membrane, its characterization (before and after cleaning) and the target application. Herein, promising membrane cleaning approaches reported in the recent years are summarized and discussed. Alternative physical, chemical and mechanical cleanings (or their combination) can be considered, even though the control of the number of cleaning cycles, cleaning conditions and combination of cleaning approaches seem to be essential to achieve an optimum global cleaning efficiency. To sum up, although further research in understanding the role of fouling in material stability and degradation after cleaning is still needed, this review provides novel insights into the definition of the most appropriate membrane cleaning strategy in different ion exchange membrane separation processes.

Influence of Loading Pressure and Sample Preparation on Ionic Concentration and Resistivity of Pore Solution Expressed from Concrete Samples

AbstractPore solution expression is an established method to obtain samples of the liquid phase from cementitious systems. This experimental method applies pressure to a cementitious sample, forcing its liquid phase out of the pores. By collecting and studying the liquid phase in cementitious systems, it is possible to obtain information on its ionic concentrations. The ionic concentrations can be used for modeling calibrations and to estimate the resistivity of the pore solution. When the bulk resistivity of concrete is normalized by the pore solution resistivity, it is possible to determine the formation factor. The formation factor is related to the transport properties of the concrete and, as such, it can be used to estimate the rates of transport of ionic species within a concrete structure. The formation factor is currently being included in AASHTO PP84, Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, as an indicator of transport properties for quality control operations. Pore solution expression is included as one of the available procedures of AASHTO PP84-19 to determine the pore solution electrical resistivity. Previous studies on paste and mortar samples have demonstrated that increased loading pressure during the pore solution expression might impact the final ionic concentrations of the expressed solution. This study aims to verify if the pore solutions of concrete specimens are also influenced by the selected loading pressure and whether the potential consequent change in the measured ionic concentrations of the solution also has an impact on its resistivity. No appreciable trend in increased solubility was observed for the range of applied normal pressures between 600 and 985 MPa. Cyclic loading regimes increased the variability of alkali solubility. Sample preparation, in some cases, influenced the water content of the sample and induced unwanted alteration on the ionic concentrations of the mixtures under study.

Fast and Selective Ionic Transport: From Ion-Conducting Channels to Ion Exchange Membranes for Flow Batteries

This review discusses selective and fast transport of ionic species (ions and their associates) through systems as diverse as ion-conducting transmembrane proteins and ion exchange membranes (IEMs) in aqueous environments, with special emphasis on the role of electrostatics, specific chemical interactions, and morphology (steric effects). Contrary to the current doctrine, we suggest that properly balanced ion-coordinating interactions are more important than steric effects for selective ion transport in biological systems. Steric effects are more relevant to the selectivity of ionic transport through IEMs. As a general rule, decreased hydration leads to higher selectivity but also to lower transport rate. Near-perfect selectivity is achieved by ion-conducting channels in which unhydrated ions transfer through extremely short hydrophobic passages separating aqueous environments. In IEMs, ionic species practically keep their hydration shell and their transport is sterically constrained by the width of aqueous pathways. We discuss the trade-off between selectivity and transport rates and make suggestions for choosing, optimizing, or developing membranes for technological applications such as vanadium-redox-flow batteries.

Layer-selective functionalisation in mesoporous double layer via iniferter initiated polymerisation for nanoscale step gradient formation

Functionalisation of technological nanopores and investigation of their transport properties have attracted considerable interest from scientific as from technological point of view, among others due to their potential regarding molecular transport design. Asymmetric design of nanopore structure and functionalisation is expected to trigger increased and directed transport of ionic species. Based on this motivation, we demonstrate a layer-selective polymer functionalisation in a mesoporous double layer thin film to generate nanoscale step gradient architectures with asymmetric charge distribution by taking advantage of co-condensation and polymer modification techniques. Thereby, mesoporous silica and co-condensed mesoporous amino silica thin films are combined to double layered films with a film thickness of 300 – 400 nm in both sequential arrangements, respectively. Iniferter initiated polymerisation is used to selectively functionalise only the amino silica layer with polymers such as poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMETAC) in a grafting from approach. Investigation of the ionic pore accessibility of the mesoporous double layered films before and after layer-selective polymer functionalisation shows that the ionic pore accessibility is dominated by the bottom layer when overcoming the electrostatic repulsion of the top layer.

Numerical Investigations into the Influence of Operational Parameters on Diffusion and Migration in Electrodialytic Nitrate Removal

A comprehensive two-dimensional (2D) macroscopic model to describe an electrodialysis system to remove nitrates from a model solution was described. This model is intended to quantify the diffusion and migration contributions to global mass transport. We have chosen nitrate removal because of its environmental and sustainability importance. No important changes in flux values are found with an increase in the flow rate, indicating that in this particular case, where only a 1:1 electrolyte is split in the central compartment, migration effects govern the transport of ionic species involved in electrodialysis. Then, the only experimental parameter that has a considerable influence is the externally applied current. The model obtained is capable of describing the electrodialytic nitrate removal. For this reason, the increment of flow rate in this kind of system must be taken carefully since pumping energy consumption by the increase in the flow rate could increase considerably. This galvanostatic model provides information that could be helpful to better understand the ED process and to improve the electrodialysis design.

Heterogeneous anion exchange membranes with nitrate selectivity and low electrical resistance

Selective transport of specific ions across ion-exchange membranes can be enhanced by controlling membrane properties such as hydrophobicity. Previous studies have shown that hydrophobic membranes enhance transport of ions with low hydration energy, although such membranes often have increased electrical resistance. In the present work, we study the separation of monovalent ions, specifically nitrate and chloride, using newly-designed heterogeneous anion-exchange membranes. These membranes show high selectivity for nitrate over chloride and have low electrical resistance. We use a functionalized polymeric binder (ionomer) and three ion-exchange resins with different hydrophobic groups, i.e., resins with quaternary ammonium groups and methyl, ethyl, and propyl substituents, respectively. We find that in electrolyte solutions with nitrate and chloride, nitrate over chloride selectivity in our membranes increases with increasing length of the alkyl groups. The membrane with propyl groups, i.e., which has the highest selectivity for nitrate, was further tested in electrolyte solutions containing nitrate, chloride, sulfate, and nitrate, chloride, iodate. The transport of sulfate and iodate ions across the membrane with propyl groups was 6% and 2% of the total counterions transport, respectively. For monovalent ions with similar hydrated size it is possible to report selectivity trends based on the ion hydration energy. We find that the chemical structure of the membrane can either promote or hinder the transport of ionic species.

Cytomorphic Electronics With Memristors for Modeling Fundamental Genetic Circuits.

Cytomorphic engineering attempts to study the cellular behavior of biological systems using electronics. As such, it can be considered analogous to the study of neurobiological concepts for neuromorphic engineering applications. To date, digital and analog translinear electronics have commonly been used in the design of cytomorphic circuits; Such circuits could greatly benefit from lowering the area of the digital memory via memristive circuits. In this article, we propose a novel approach that utilizes the Boltzmann-exponential stochastic transport of ionic species through insulators to naturally model the nonlinear and stochastic behavior of biochemical reactions. We first show that two-terminal memristive devices can capture the non-linear and stochastic behavior of biochemical reactions. Then, we present the design of several building blocks based on analog memristive circuits that inherently model the biophysical mechanisms of gene expression. The circuits model induction by small molecules, activation and repression by transcription factors, biological promoters, cooperative binding, and transcriptional and translational regulation of gene expression. Finally, we utilize the building blocks to form complex mixed-signal networks that can simulate the delay-induced oscillator and the p53-mdm2 interaction in the cancer signaling pathway. Our approach can provide a fast and simple emulative framework for studying genetic circuits and arbitrary large-scale biological networks in systems and synthetic biology. Some challenges may be that memristive devices with frequent learning and programming do not have the same longevity as traditional transistor-based electron-transport devices, and operate with significantly slower time constants, which can limit emulation speed.

In Situ Growth Visualization Nanochannel Membrane for Ultrasensitive Copper Ion Detection under the Electric Field Enrichment.

The transport of ionic species through nanochannels plays an important role in the basic research and practical application of nanofluidic devices. Here, a visualized CdSe@ZIF-8/PAA nanochannel membrane was created by employing in situ growth of zeolite imidazole skeleton (ZIF-8) and CdSe quantum dots (CdSe QDs) on a porous anodized aluminum oxide (PAA) membrane surface using CdSe QDs, 2-methylimidazole, and zinc nitrate as the precursor solvents. ZIF-8 is a kind of metal-organic framework, a microporous material that possesses strong metal adsorption capacity. In addition, CdSe quantum dots have fluorescent properties. The nanochannel membrane detects copper ions (Cu2+) by quenching the fluorescence intensity by the interaction between Cu2+ and Se and S atoms. The direct potential of 5 V was applied to achieve Cu2+ enrichment at the nanochannel interface, and the fluorescence change was observed. The CdSe@ZIF-8/PAA nanochannel membrane has a good linear range of concentration (0.01 pM-1 μM) for Cu2+ detection. With the help of nanochannel enrichment, its detection limit reaches 4 fM. In addition, this nanochannel membrane has good selectivity for Cu2+.