Ion Partitioning Research Articles

Effect of ion partitioning on an oscillatory electro-osmotic flow on solute transport process of fractional Jeffrey fluid through polyelectrolyte-coated nanopore with reversible wall reaction

The ion-partitioning effects on solute transport phenomena of time-periodic electro-osmotic flow in fractional Jeffrey fluid are investigated through a polyelectrolyte layer (PEL)-coated conical nanopore within a reactive wall whose ends are connected with two large reservoirs. By considering the ion-partitioning effects, analytical solutions for the induced potential and the axial velocity are presented, respectively, from the modified Poisson–Boltzmann equation and the Cauchy momentum equation with the proper constitutive equation of the fractional Jeffrey fluid model in the exterior and interior of the PEL. The analytic solution of the convection–diffusion for solute transport is established in the entire domain. The influence of the oscillating Reynolds number Rew, permittivity ratio εr between two mediums, relaxation time λ1ω, retardation time λ2ω, phase partitioning coefficient σp, PEL fixed charge density qfix, Debye–Hückel parameter κa, and softness parameter λs are investigated in this study. Asymptotic solution for the axial velocity was also presented for low-oscillating Reynolds numbers and validated. The maximum axial velocity occurs when the permittivity between the PEL and electrolyte is the same for all models. The volumetric flow rate decreases with the increase in the PEL thickness, positive PEL charge density, and softness parameter in our study. The volume flow rate of the Newtonian fluid increased 24.07% for Maxwell fluid (λ1ω=5, α = 1) and 11.56% for Jeffrey fluid (λ1ω=5, λ1ω=1, α = 1, and β=0.5), when κa=25, Rew = 10, qfix = 5, d = 0.2, εr=0.6, and λs=1.0. The mass transport rate increases with relaxation time, tidal displacement, and permittivity ratio between these layers.

Mechanisms for enhanced transport selectivity of like-charged ions in hydrophobic-polymer-modified ion-exchange membranes

Effectively removing contaminants or extracting resources from water necessitates selective separation of ions with toxicity or economic value from common ions. Existing ion exchange membranes (IEM) effectively separate ions with opposite charges, but are not optimized for separating ions of like charges. An understanding of ion separation mechanisms is imperative for developing IEMs with improved selectivity between like-charged ions. In this work, we modify a commercial anion exchange membrane (AEM) with a hydrophobic polymer, polypyrrole (PPy), and show that PPy-modified AEM exhibits enhanced transport selectivity of nitrate over both chloride and sulfate. Combining ion sorption experiments and molecular dynamics simulations, we show that the enhanced selectivity between nitrate and chloride is attributed to the decoupling of the inverse relation between the ion partition into and diffusion within the polymer phase, which improves the overall ion transport selectivity between like-charged ions.

Thermodynamic and kinetic modeling the interaction of goethite-ligand-metal ternary system

Low-molecular-weight organic acids may significantly influence the mobility of metal in environment, but the kinetics are not fully understood and have not been quantified. In this study, the thermodynamic and kinetic effects of citric acid (CA) on the adsorption of Cd(II) and Ni(II) on goethite were investigated using batch-adsorption and stirred-flow experiments. A charge distribution and multisite complexation model (CD-MUSIC) and a thermodynamically based multi-rate kinetic model were employed to describe the adsorption behaviors. Two ternary surface complexes, (≡FeO)2CitMe and (≡FeOH)2MeCit2−, were involved in the adsorption. In addition, CA differed in its effects on Cd(II) and Ni(II) adsorption, enhancing Cd(II) adsorption but inhibiting Ni(II) adsorption at high levels. Kinetically, in the presence of CA, the adsorption of Cd(II) was faster than that of Ni(II). Increasing CA concentration led to faster Cd(II) adsorption, but resulted in the dissolution of the adsorbed Ni(II), possibly due to the much higher complexation constants of Ni-CA than of Cd-CA in aqueous phase. This finding implied that, in the rhizosphere, high level of CA may lead to more dissolution of Ni(II) than Cd(II); while in acidic ferrosol, CA may alleviate Cd(II) mobility and toxicity. The proposed mechanistic model sheds light on ion partition in the soil environment and may improve predictions thereof.

Dynamic model of monovalent-divalent cation exchange in polyelectrolyte gels

A multicomponent model that imposes conservation laws and constitutive relations for polymer chains, water, and ions was investigated by determining the transient changes in a negatively charged gel exposed to a solution containing both mono- and divalent cations. Association of ion exchange with gel volume is achieved by imposing a linear relation between the polymer-solvent interaction parameter and concentration of divalent cations adsorbed onto the polymer chains. Semiquantitative agreement with measurements made on sodium polyacrylate gels is demonstrated in three aspects: (1) dynamics of gel swelling and deswelling, (2) ion partitioning coefficient, and (3) effect of cross-link density. These results imply that the multicomponent coarse-grained continuum modeling approach can be useful for quantitative predictions over macroscopic length and timescales including the description of volume transitions exhibited by these systems.

Systematic evaluation of hydrophobic deep eutectic solvents as alternative media for the extraction of metal ions from aqueous solution

The recent development of hydrophobic deep eutectic solvents (HDESs) has led to growing interest in these reagents as possible environmentally benign replacements for conventional organic media in a host of applications, among them metal ion separations by liquid-liquid extraction. To evaluate the potential utility of these novel solvents in this application, a systematic examination of the facilitated transfer of selected alkali and alkaline earth cations into representative HDESs from aqueous solution in the presence of a macrocyclic polyether (i.e., a crown ether) has been undertaken. Comparison of the results to those obtained for a series of oxygenated, aliphatic solvents (n-alcohols) and for several 1-alkyl-3-methylimidazolium-based ionic liquids (ILs) under the same conditions indicate that despite frequent suggestions that some HDESs resemble ILs, metal ion distribution in HDES-aqueous systems more closely mimics that seen for the alcohols. Metal ion partitioning in these systems appears less dependent on the water content of the organic phase and on structural variations in the solvent than is the case for either alcohols or ionic liquids, however. The implications of these results for the design and application of HDES-based extraction systems for metal ions are described.

Adsorption of Hydrophilic Silica Nanoparticles at Oil-Water Interfaces with Reversible Emulsion Stabilization by Ion Partitioning.

Adsorption of particles at oil-water interfaces is the basis of Pickering emulsions, which are common in nature and industry. For hydrophilic anionic particles, electrostatic repulsion and the absence of wetting inhibit spontaneous adsorption and limit the scope of materials that can be used in emulsion-based applications. Here, we explore how adding ions that selectively partition in the two fluid phases changes the interfacial electric potential and drives particle adsorption. We add oil-soluble tetrabutyl ammonium perchlorate (TBAP) to the nonpolar phase and Ludox silica nanoparticles or silica microparticles to the aqueous phase. We find a well-defined threshold TBAP concentration, above which emulsions are stable for months. This threshold increases with the particle concentration and with the oil's dielectric constant. Adding NaClO4 salt to water increases the threshold and causes spontaneous particle desorption and droplet coalescence even without agitation. The results are explained by a model based on the Poisson-Boltzmann theory, which predicts that the perchlorate anions (ClO4-) migrate into the water phase and leave behind a net positive charge in the oil. Our results show how a large class of inorganic hydrophilic, anionic nanoparticles can be used to stabilize emulsions in a reversible and stimulus-responsive way, without surface modifications.

Salt Tolerant Eggplant Rootstocks Modulate Sodium Partitioning in Tomato Scion and Improve Performance under Saline Conditions

Grafting on salt tolerant eggplant rootstocks can be a promising approach for enhancing the salinity tolerance of tomato. In this study, the performance of tomato cv. Kashi Aman grafted on two salt tolerant eggplant rootstocks (IC-111056 and IC-354557) was evaluated against non-grafted control under saline (ECiw 6 and 9 dS m−1) and non-saline (ECiw ~1 dS m−1) irrigation for 2 years. Grafting improved tomato plant performance under salt stress. Moreover, rootstock IC-111056 outperformed IC-354557. An increase in the average fruit yield of grafted plants compared with non-grafted control at 6 and 9 dS m−1 was 24.41% and 55.84%, respectively with rootstock IC-111056 and 20.25% and 49.08%, respectively with IC-354557. Grafted plants maintained a superior water status under saline irrigation, evidenced with the relative water content and chlorophyll SPAD index, along with higher proline and antioxidant enzyme activities (superoxide dismutase, catalase, and ascorbate peroxidase). Rootstocks mediated the partitioning of toxic saline ions in the scions by promoting higher Na+ accumulation (14% of mean accumulation) in the older leaves and lower (24%) in the younger leaves of grafted plants. This resulted in higher K+/Na+ ratios within the younger (active) leaves of the grafted plants. Our study demonstrates that grafting tomato seedlings on selected salt tolerant eggplant rootstocks is a viable alternative for improving plant physiological status and fruit yield under salt stress, through favorable modulation of salt ion partitioning in the scions.

Phase equilibrium and ionic liquid partitioning in aqueous two-phase system composed of alcohol and small molecule compound

Phase equilibrium and ionic liquid partitioning in aqueous two-phase system composed of alcohol and small molecule compound

Correction to “Grand-Reaction Method for Simulations of Ionization Equilibria Coupled to Ion Partitioning”

Correction to “Grand-Reaction Method for Simulations of Ionization Equilibria Coupled to Ion Partitioning”

Manning condensation in ion exchange membranes: A review on ion partitioning and diffusion models

AbstractThe rational design of ion exchange membranes (IEMs) is becoming more pertinent as their usage becomes broader and as their staple applications (i.e., electrodialysis, flow batteries, and fuel cells) improve in commercial viability. Such efforts would be catalyzed by an improved fundamental understanding of ion transport in IEMs. This review discusses recent progress in modeling ion partitioning and diffusion in IEMs in an effort to relate IEM performance metrics to fundamental membrane properties over which researchers and membrane manufacturers possess direct and sometimes precise control. Central focus is given to the Donnan‐Manning model for ion partitioning and the Manning‐Meares model for ion diffusion in IEMs. These two frameworks, which are derived from Manning's counter‐ion condensation theory for polyelectrolyte solutions, have been widely used within the IEM literature since their recent introduction. To explore this topic, the mathematical derivation of both models is revisited, followed by a survey of experimental and computational discussions of counter‐ion condensation in IEMs. Alternative models which fulfill similar roles in predicting IEM transport properties are compared. This review concludes by highlighting the uniquely favorable positions of the Donnan‐Manning and Manning‐Meares models and discussing their prospects as leading predictors of IEM partitioning and diffusive properties.

Increased Donnan exclusion in charged polymer networks at high salt concentrations.

The swelling of univalent and multivalent charged polymeric networks in electrolytic solutions is studied using a classical thermodynamic model. Such systems were first modeled by Donnan, who derived an expression for the chemical potential of the ions by introducing an electric potential that is commonly referred to as the Donnan potential. This well-established theory leads to a simple quadratic relationship for the partitioning of ions between the network and the external solution. When the concentration of fixed charges in the swollen gel is large enough, the electrolyte in the external solution is "excluded" from the gel (commonly referred to as Donnan exclusion). In the standard Donnan theory, and in virtually all subsequent theories, the magnitude of Donnan exclusion decreases with increasing electrolyte concentration in the external solution. Our model predicts this is not necessarily true; we show that the magnitude of Donnan exclusion increases with increasing electrolyte concentration over a broad range of parameter space (average chain length between crosslinks, fraction of charged monomers in the network, the nature of the interactions between the ions, solvent molecules and polymer chains, and ion concentration in the external solution). We also present explicit bounds for the validity of Donnan's original theory. Model predictions are compared to simulations and experimental data obtained for a cationic gel immersed in electrolytic solutions of salts containing univalent and bivalent cations.

Salt Sensitivity in Soybean: Growth, Photosynthesis, Tissue and Cellular Ion Partitioning in Three Soybean Genotypes

Salt Sensitivity in Soybean: Growth, Photosynthesis, Tissue and Cellular Ion Partitioning in Three Soybean Genotypes

Impact of asymmetry soft layers and ion partitioning on ionic current rectification in bipolar nanochannels

When both positive and negative charges are present at the nanochannel surface, the system is called a bipolar nanochannel, or bipolar diode. Bipolar nanochannels have a much higher degree of rectification than unipolar nanochannels with asymmetric geometries because, in the backward mode, pass on an ionic current close to zero. In modeling bipolar soft nanochannels, it is usually assumed that the properties of the soft layer (PEL) and electrolyte are the same, which is not valid for soft layers with high charge densities. In the present work, the effect of considering different properties for the soft layer and electrolyte on the ion current rectification in cylindrical bipolar soft nanochannels was studied. To this end, by utilizing a numerical computational procedure using the finite element method (FEM), Poisson-Nernst-Planck (PNP) and Navier-Stokes (NS) equations were solved for steady-state conditions by considering different permittivities, diffusion coefficients, and dynamic viscosities for PEL and electrolyte. The model findings, which were verified through comparing with the existing theoretical data, revealed that considering differences in the properties of the soft layer and electrolyte led to a significant improvement in the rectification factor. For instance, at the bulk concentration of c0=10mM, the rectification factor of 695 for a bipolar cylindrical soft nanochannel at ηε=ημ=1,ηD=2 reached a value of 13430 at ηε=ηD=0.6,ημ=2. For a similar system, at a bulk concentration of c0=1mM and a symmetric soft layer Rs,p=Rs,n=5nm the value of Rf was 1822, and it reached a value of nearly twice, i.e. 3535, where an asymmetric soft layer Rs,p=3nm<Rs,n=7nm was applied.

Development of suberized barrier is critical for ion partitioning between senescent and non-senescent tissues in a succulent halophyte Sarcocornia quinqueflora

Senescence of plant tissues is a physiologically synchronized process that enables an evergreen or a perennial plant to retrieve, recycle and remobilize nutrients from elder to younger tissues or upcoming seeds. The succulent perennial halophyte S. quinqueflora utilizes this process to discard excess salt being accumulated in outer tissues of their leafy stems. The exact mechanism for salt shedding in this plant, however, remains elusive. In this work we show that the plant develops two distinct types of tissues - an endodermis-like layer (suberized layer, ED), and an additional internal photosynthetic layer (IP) - to enable this process. Their potential roles toward salt-coping strategy were investigated in this study. We show that elevated salinity leads to an accelerated development of the ED, and that its development strongly affected ion partitioning between outer (senescent) and inner (non-senescent) tissues. A positive correlation between the ratio of ED to a bead diameter and the outer to inner concentration of Na+ was observed. These ratios were highest in older (basipetally-located) beads and progressively decreased towards the tip. Furthermore, the Na+/ K+ ratio in inner tissues of bottom beads at highest salinity treatments (800 and 1000 mM NaCl) that showed clear senescence symptoms was ∼1.0, indicative of complete separation of the outer and inner tissues at late developmental stage due to the fully suberized ED multilayer. A dual-sources: dual-sinks model explaining the role of the IP layer in plant adaptation to salinity is presented.

Electrochemical behavior of cocaine cutting agents at the polarized liquid-liquid interface

In this work, we have used cyclic voltammetry to investigate the interfacial behavior of cocaine cutting agents at the electrified liquid-liquid interface formed between a solution of the water and 1,2-dichloroethane phases. Among 27 chemical species used to adulterate cocaine street samples, only 8 were detectable in the available potential window. These include procaine, lidocaine, levamisole, hydroxyzine, caffeine, phenylethylamine, diltiazem, and diphenhydramine. From the calibration curves obtained using voltammetric data, we have extracted the electroanalytical parameters such as detection sensitivities, limits of detection, and limits of quantifications. Also, for each electrochemically active drug, we have calculated diffusion coefficients and plotted the ion partition and concentration fraction diagrams. All this information is discussed in a view of the cocaine sensors development focused on its detection from demanding matrix defined by the street samples composition.

Influence of divalent ions on composition and viscoelasticity of polyelectrolyte complexes

AbstractThe addition of monovalent salts to polyelectrolyte complexes (PECs) comprising oppositely charged polyelectrolytes results in diminishing propensity for complexation, leading to complexes with higher water contents and lower moduli. However, the corresponding influence of multivalent ions on polyelectrolyte complexation has not yet been explored beyond enhanced screening effects. Here, we elucidate the significant impact of the valency of the salt cation on the composition, ion partitioning, and viscoelasticity of charge‐matched PECs comprising sodium salt of poly(acrylic acid) and poly(allylamine hydrochloride). Notably, preferential partitioning of divalent cations (Ca2+ and Sr2+) into the complexes is observed, in stark contrast to the depletion of monovalent ions (Na+) from the complexes. Concomitantly, electrostatic bridging of polyanion chains by divalent ions is found to hinder their relaxation, manifesting as a non‐monotonic evolution of the shear moduli of the complexes with increasing divalent salt concentrations. Relatedly, a failure of time‐salt and time‐ionic strength superposition approaches in presence of divalent ions is demonstrated, highlighting the nontrivial influence of these ions on chain relaxation behavior.

Ion partitioning effect on the electrostatic interaction between two charged soft surfaces

We theoretically investigate electrostatic properties between two charged surfaces with a grafted polyelectrolyte layer in an aqueous electrolyte solution by using the Poisson-Boltzmann approach accounting for ion partitioning. In order to consider the ion partitioning effect, we focus on changes of electrostatic properties due to the difference in dielectric permittivity of the polyelectrolyte layer and the aqueous electrolyte solution. We find that ion partitioning enhances electrostatic potential in the region between two charged soft surfaces and hence increases the electrostatic interaction between two charged soft surfaces. Ion partitioning effect on osmotic pressure is enhanced not only by an increase in the thickness of polyelectrolyte layer and Debye length but also by a decrease in ion radius.

Impacts of the temperature-dependent properties on ion transport behavior in soft nanochannels

The influence of the temperature- and concentration-dependent properties, derived from the gradients of temperature and concentration, on the ionic selectivity, ionic current rectification, Joule heating, and viscosity dissipation in conical soft nanochannels was numerically investigated. Both co-current an counter-current modes of operation, in terms of implementing temperature- and concentration gradients, were considered. Since it was assumed that the nanochannel is coated with a dense polyelectrolyte layer, the ionic partitioning effect was also considered. Through adopting a numerical approach, Poisson–Nernst–Planck, Navier–Stokes, and energy equations were solved at steady-state conditions by considering different values of permittivity, diffusivity, and viscosity for the PEL and the electrolyte. The most important result of this study is that under an applied voltage, by increasing the temperature and concentration ratios, the Joule heating increased. For instance, at counter-current mode, by increasing the concentration ratio from 1 to 100, the Joule heating increased from 1 nW to 3.5 nW. It was also realized that upon applying an external voltage of Vapp = − 5 V, the Joule heating reaches a value of 130 nW. As such, it was concluded that the lack of control in the generation of Joule heating would harm the transport behavior of ionic species within soft nanochannels.

Impacts of the shape of soft nanochannels on their ion selectivity and current rectification

The influence of channel geometry on the ion selectivity and ionic current rectification (ICR) of soft nanochannels was numerically investigated. The nanochannels coated with polyelectrolyte layers (PELs) are termed as soft nanochannels. Two categories of channels, asymmetric (trumpet, conical, bullet, and cigar-like) and symmetric (cylindrical), were considered in this study. When PEL is dense, the ionic partitioning effect can not be ignored. To this end, through adopting a numerical approach using the finite element method (FEM), Poisson-Nernst-Planck and Navier-Stokes equations were solved at steady-state conditions by considering different values of permittivity, diffusivity, and dynamic viscosity for the PEL and the electrolyte. The model findings were verified by comparing them with the existing simulation data. For the cylindrical type nanochannels, the results indicate that the rectification factor is approximately equal to unity, and the ion selectivity at positive voltages is approximately equal to that at negative voltages. For other geometries, the ion selectivity factor of the channel was STrumpet>SConical>SBullet>SCigar. On the other hand, at low bulk concentrations, the rectification factor was RfCigar>RfBullet>RfConical>RfTrumpet, while at high bulk concentrations, it was RfBullet>RfCigar>RfConical>RfTrumpet. Considering a charge density of 80mol/m3 and a bulk concentration of 20mM, we demonstrate that the rectification factors for the bullet and trumpet types nanochannels, from 3.35and0.56 by ignoring the ion partitioning effect, can reach the values of 5.78 and 0.83 by considering the ion partitioning effect, respectively.

Competition between Born solvation, dielectric exclusion, and Coulomb attraction in spherical nanopores.

The recent measurement of a very low dielectric constant, ε, of water confined in nanometric slit pores leads us to reconsider the physical basis of ion partitioning into nanopores. For confined ions in chemical equilibrium with a bulk of dielectric constant ε_{b}>ε, three physical mechanisms, at the origin of ion exclusion in nanopores, are expected to be modified due to this dielectric mismatch: dielectric exclusion at the water-pore interface (with membrane dielectric constant, ε_{m}<ε), the solvation energy related to the difference in Debye-Hückel screening parameters in the pore, κ, and in the bulk κ_{b}, and the classical Born solvation self-energy proportional to ε^{-1}-ε_{b}^{-1}. Our goal is to clarify the interplay between these three mechanisms and investigate the role played by the Born contribution in ionic liquid-vapor (LV) phase separation in confined geometries. We first compute analytically the potential of mean force (PMF) of an ion of radius R_{i} located at the center of a nanometric spherical pore of radius R. Computing the variational grand potential for a solution of confined ions, we then deduce the partition coefficients of ions in the pore versus R and the bulk electrolyte concentration ρ_{b}. We show how the ionic LV transition, directly induced by the abrupt change of the dielectric contribution of the PMF with κ, is favored by the Born self-energy and explore the decrease of the concentration in the pore with ε both in the vapor and liquid states. Phase diagrams are established for various parameter values and we show that a signature of this phase transition can be detected by monitoring the total osmotic pressure as a function of R. For charged nanopores, these exclusion effects compete with the electrostatic attraction that imposes the entry of counterions into the pore to enforce electroneutrality. This study will therefore help in deciphering the respective roles of the Born self-energy and dielectric mismatch in experiments and simulations of ionic transport through nanopores.