Ion Size Effects Research Articles

Dielectric Properties of Aqueous Electrolyte Solutions Confined in Silica Nanopore: Molecular Simulation vs. Continuum-Based Models.

Dielectric behavior of electrolyte aqueous solutions with various concentrations in a cylindrical nanopore of MCM 41 silica has been investigated. The effect of confinement is investigated by using isothermal-isosurface-isobaric statistical ensemble, which has proved to be an effective alternative to the Grand Canonical Monte Carlo (GCMC) simulation method. Several single-salt solutions have been considered (e.g., NaCl, NaI, BaCl2, MgCl2) in order to investigate the effect of ion polarizability, ion size, and ion charge. The effect of salt concentration has also been addressed by considering NaCl solutions at different concentrations (i.e., 0.1 mol/L, 0.5 mol/L, and 1 mol/L). The motivation in performing this integrated set of simulations is to provide deep insight into the dielectric exclusion in NF theory that plays a significant role in separation processes. It was shown that the dielectric constant increased when ions were added to water inside the nanopore (with respect to the dielectric constant of confined pure water) unlike what was obtained in the bulk phase and this phenomenon was even more pronounced for electrolytes with divalent ions (MgCl2 and BaCl2). Therefore, our simulations indicate opposite effects of ions on the dielectric constant of free (bulk) and nanoconfined aqueous solutions.

Ion size effect on the diffusiophoretic mobility of a large colloidal particle

Ion size effect on the diffusiophoretic mobility of a large colloidal particle

Finite Ion Size Effects on Ionic Flows via Poisson–Nernst–Planck Systems: Higher Order Contributions

Finite Ion Size Effects on Ionic Flows via Poisson–Nernst–Planck Systems: Higher Order Contributions

Finite ion size and ion permittivity effects on gel electrophoresis of a soft particle

Electrophoresis of a soft particle embedded in a hydrogel medium is studied by considering the hydrated ions as charged dielectric spheres of finite radius. The Nernst-Planck equation for the transport of ions is modified to take into account the ion steric repulsion and the ion-solvent dielectric interactions (MNP-model). The effective polarizability of the hydrated ions lowers the dielectric permittivity of the ionic solution and consequently, the permittivity of the medium varies with local ionic concentration. This spatial variation of the permittivity creates a Born energy difference in ions leading to a Born force experienced by the ions. In addition, ions experience a dielectrophoretic force due to the polarization under the imposed external electric field. The ion steric repulsion are modeled by the Carnahan-Starling equation of state. The convection of ions are governed by the Brinkman extended Navier-Stokes equations. The modified Nernst-Planck equation coupled with the Brinkman Navier-Stokes equations and the equation for electric field are solved numerically through a control volume approach. The ion steric interactions and ion-solvent interactions create a saturation of mobile ions in the polyelectrolyte layer (PEL) of the soft particle, which leads to an attenuation of the counterion condensation of the PEL. This short range steric repulsion and ion-solvent interactions have significance for higher bulk ionic concentration as well as higher range of charge density of the soft particle. These interactions are elucidated by comparing with the mobility obtained by the standard model (PNP-model). The Dukhin number and the effective charge density of the PEL are determined to illustrate the mobile ion saturation. The discrepancy between the present modified model from the standard model magnifies for the case of salts of multivalent counterions.

Development of Absorbent Using Amylose-Graphite Composite Electrode for Removal of Heavy Metals.

Amylose of Phragmites Australis captures heavy metals in a box consisting of sugar chains. However, its absorption rate is low in the period of the month scale. Therefore, the electrochemical driving force was used to promote the absorption rate in this research. Amylose was doped with TiO2 porous graphite electrode. The composted absorbent was characterized using XRD(X-ray diffraction), SEM (Scanning Electrode Microscopy), Raman spectroscopy, and electrochemical methods. The affinity and maximum absorption amount were calculated using the isotherm method. In this study, Pb2+, Cu2+, Cd2+, and Cr6+ were chosen to demonstrate because these heavy metals are significant pollutants in Japan’s surface water. It was found that the maximum absorption was Cu2+ (56.82-mg/L) > Pb2+ (55.89-mg/L) > Cr6+ (53.97-mg/L) > Cd2+ (52.83.68-mg/L) at −0.5 V vs. Ag/AgCl. This is approximately the same order as the hydration radius of heavy metals. In other words, the absorption amounts were determined by the size of heavy metal ions. Subsequently, the mixed heavy metal standard solution was tested; the maximum absorption amount was 21.46 ± 10.03 mg/L. It was inferred that the electrochemical driving force could be shown as the ion size effect in the mixed solution. Despite there being no support for this hypothesis at this time, this study succeeded in showing that the electrochemical driving force can improve the ability of the absorbent.

Electrophoresis of Liquid-Layer Coated Particles: Impact of Ion Partitioning and Ion Steric Effects.

The biomimetic core-shell nanoparticles coated with membranes of various biological cells have attracted significant research interest, because of their extensive applications in targeted drug delivery systems. The cell membrane consists of a lipid bilayer, which can be regarded as a two-dimensional oriented viscous liquid with low dielectric permittivity, compared to a bulk aqueous medium. Such a liquid layer comprised of cell membrane may bear additional mobile charges, because of the presence of free lipid molecules or charged surfactant molecules, which further results in nonzero charge along the surface of the peripheral layer. In this article, we present an analytical theory for electrophoresis of such cell membrane coated functionalized nanoparticles in the extent of electrolyte solution, considering the combined effects of finite ion size and of ion partitioning. Going beyond the Debye-Huckel approximations, we propose an analytical theory for Donnan potential and electrophoretic mobility. The derived expressions are applicable for moderate to highly charged undertaken core-shell particles when the thickness of the peripheral liquid layer greatly exceeds the electric double layer thickness. The impact of pertinent parameters on the electrophoretic response of such a particle is further discussed.

Modeling the Gouy–Chapman Diffuse Capacitance with Attractive Ion–Surface Interaction

The interfacial capacitance of a metal electrode in contact with a dilute electrolyte is generally expected to follow the behavior predicted by the Gouy–Chapman–Stern model. Recent experiments [Angew. Chem. Int. Ed. 2020, 59, 711], however, have shown that a deviation from the Gouy–Chapman behavior is observed even in dilute electrolytes on platinum and gold single-crystal electrodes. Such deviations are usually attributed to an interaction between the surface and the electrolyte ions. However, a quantitative model showing that the strong deviations from the Gouy–Champan behavior observed for Pt can be ascribed to such an effect is still lacking, particularly as other experimental observables do not indicate a strong ion adsorption. Here, we propose a double-layer model that is capable of reproducing the main experimental findings in a simple and (in parts) analytical way. The analytical model thereby includes the attractive ion–surface interaction via an additional capacitive element connected in parallel to the Gouy–Chapman capacitance. By comparing the model predictions to experiment, we subsequently infer characteristics of the ion–surface interaction. In particular, we find that the model predicts the attractive interaction to be weak (weaker than a typical chemical bond formed when contact adsorbing) and that the interaction has to be very similar for all ions. Furthermore, for a good agreement with experiment, ion-size effects are suggested to play a role in determining the potential of minimum capacitance.

Classical density functional analysis of the ionic size effects on the properties of charge regulating electric double layers

The focus of the present article is on the ionic size variation effects on the properties of charged interfaces involving electrolyte solution, commonly referred to as electric double layers. The presence of a well defined charged interface between the solution and a substrate has a profound impact on the local structure of the liquid phase. All solution species are distributed according to the various fluid and surface interactions. The excluded volume and finite dimensions of all ions and the solvent molecules are a major contributor to the detailed liquid structure. The structure determines important properties of the electric double layers such as charge and potential distributions and the surface and in the fluid. Our analysis is based on using classical density functional theory, which allows one to account for a variety of Coulombic and non-Coulombic interactions. The surface charge is determined by the thermodynamic equilibrium with potential determining species in the solution. We demonstrate that the size variation of the background electrolyte ions has a strong impact on the surface chemical equilibrium, as well as on the structure, charge and potential distributions in the electric double layer.

Exploring the Influences of Nanoparticle Synthesis-Route and Electrolytic Ions on the Electrochemical Performance of MnFe2O4-Based Supercapacitors

A facile and cost-effective synthesis of MnFe2O4 nanoparticles (MnF NPs) using solvothermal and co-precipitation method are explored. The structure, chemical coating, morphology, surface area, and pore size distribution of the NPs are characterized using XRD, FTIR, Raman, TGA, FESEM, EDAX, BET, and BJH analysis. This work investigates the supercapacitive performance of MnF NPs from two different perspectives; (i) influences of the synthesis methods, and (ii) the effect of solvated electrolytic ion size. The conclusion drawn from the morphological studies indicates that the co-precipitation method is more efficient in synthesizing nanoparticles with a smaller diameter and uniform distribution. The electrochemical performances of the NPs are evaluated using CV, GCD, and EIS techniques in 3.5 M KOH solution. NPs prepared by co-precipitation approach show higher specific capacitance of 1334 F/g at 2.5 A/g while the value for solvothermally synthesized sample is 786 F/g. These enhanced electrochemical properties are attributed to the smaller particle size, presence of an ample number of electro-active sites, better electronic conductivity of MnF, and multiple oxidation states of manganese and iron ions. Furthermore, the effect of electrolyte ionic radii on the electrochemical properties of the prepared samples is studied. The different aqueous electrolyte of alkaline nature is selected for the experiment. 3.5 M of LiOH, NaOH, and KOH are used to explore the effect of solvated ion size on the electrochemical performance of the MnF NPs. A rising trend of specific capacitance is observed according to the ionic mobility (K+ >Na+ >Li+) of the electrolytic cations. The capacitance of solvothermally synthesized MnF NPs is increased nearly twice with changing the cation from Li+ to K+ ions. The specific capacitance observed for MnF NPs synthesized by the co-precipitation approach are found to be 1002, 1125, and 1334 F/g at a current density of 2.5 A/g for LiOH, NaOH, and KOH, respectively. Among these, KOH-based electrolytes exhibit better activity, capacitance retention, rate performance, ionic conductivity, efficient charge or ion diffusion, and relaxation time. Apart from this, mechanistic studies using the Trasatti method and power-law are used to investigate the electrochemical behaviours of the prepared NPs. The study implies that the redox process of the NPs is diffusion controlled. The diffusion process contributes significantly to the overall charge storage properties of the NPs. This study infer that the co-precipitation approach is favorable in terms of time, cost, eco-friendliness and higher charge storage properties whereas KOH-based alkaline electrolyte is the best-suited to achieve better performance of supercapacitor. This suggests that the preparation method of NPs and the electrolytes play significant role on the performance of electrochemical capacitors.

First-principles study of the composition, cation arrangement, and local structure in high-performance Bi(Me3+)O3–PbTiO3 (Me3+ = Ga, Sc, In) ferroelectric solid solutions

Ferroelectric perovskite solid solutions are of interest due to their extensive use in modern electronic devices. Cation off-centering is the dominant mechanism of ferroelectricity in perovskite oxides, and it was shown that the average off-centering of these cations can be used to predict some of the essential properties of solid solutions. In this work, we use first-principles density functional theory to investigate the dependence of the cation displacements on the ionic size, amount of substitution, O6 tilt, and locations of the Bi and Me3+ cations in xBiMe3+O3–(1 − x)PbTiO3 (Me3+ = Ga, Sc, In) solid solutions. We carry out our calculations for the x = 0.125 and x = 0.25 BiMe3+O3 substitution concentrations and the ⟨100⟩, ⟨110⟩, ⟨111⟩, ⟨011⟩, and ⟨001⟩ arrangements of the BiMe3+O3 substituent units. We demonstrate that the substitution of larger ions leads to greater variation in the energy and cation displacement magnitudes of the different cation arrangements. Our study reveals that cation displacements are governed by the interplay of the volume expansion effect that favors higher displacements and the cooperative O6 tilt effect that decreases the displacements. Both of these effects increase with greater ionic radius and their relative strengths depend on the cation arrangement. We also illustrate how negative pressure can be achieved experimentally by the doping of large In cations in these solid solutions. Understanding the dependence of the different directional arrangements, O6 tilting, and the effect of ionic size is important for precise prediction of ferroelectric materials properties and enables rational design of new piezoelectric materials.

Highly Tunable Multifunctional BaTiO3-Based Ferroelectrics via Site Selective Doping Strategy

Electric-field-driven polarization in ferroelectrics delivers extraordinary electro-caloric, electro-optic, and electromechanical properties, etc. However, the controllable multifunctional ferroelectric switching between different electro-related performances still faces great challenges and deserves study. Herein, multifunctional BaTiO3 (BT)-based ferroelectrics are conceived tuning electrocaloric and electrostrictive properties by controlling doping site of dopants, namely site selective doping strategy. The well-concerned Ce is selected for its multivalent trait (Ce3+/Ce4+) and effective adjustment of Curie temperature (TC) in BT. Guided by the distinguished dielectric characteristics via doping Ce3+ in Ba site or Ce4+ in Ti site, BT-based ferroelectrics can direct at different applications. For Ba-site doping, in conjunction with ion-size mismatch effect and defect engineering, manipulating TC to room temperature (RT) and driving second-order-like phase transition are obtained simultaneously. Then, large electrocaloric temperature change (∆Tmax=1.3 K) over a broad temperature span (∆T>1 K, 37~70 ℃) is achieved, which is crucial in developing zero-global-warming-potential refrigeration near RT. For Ti-site doping, unique diffuse phase transition is observed without sacrificing TC, leading to multiphase structures and the formation of nanosize domains, hence facilitating polarization rotation. Therefore, an enhanced electrostrictive strain (S>0.17%) with ultra-low hysteresis (Hhyst<5%) among a wide temperature range is obtained, which challenges toxic lead-contained counterparts in actuators.

Numerical study of the vortex-induced electroosmotic mixing of non-Newtonian biofluids in a nonuniformly charged wavy microchannel: Effect of finite ion size.

We propose a micromixer for obtaining better efficiency of vortex induced electroosmotic mixing of non-Newtonian bio-fluids at a relatively higher flow rate, which finds relevance in many biomedical and biological applications. To represent the rheology of non-Newtonian fluid, we consider the Carreau model in this study, while the applied electric field drives the constituent components in the micromixer. We show that the spatial variation of the applied field, triggered by the topological change of the bounding surfaces, upon interacting with the non-uniform surface potential gives rise to efficient mixing as realized by the formation of vortices in the proposed micromixer. Also, we show that the phase-lag between surface potential leads to the formation of asymmetric vortices. This behavior offers better mixing performance following the appearance of undulation on the flow pattern. Finally, we establish that the assumption of a point charge in the paradigm of electroosmotic mixing, which is not realistic as well, under-predicts the mixing efficiency at higher amplitude of the non-uniform zeta potential. The inferences of the present analysis may guide as a design tool for micromixer where rheological properties of the fluid and flow actuation parameters can be simultaneously tuned to obtain phenomenal enhancement in mixing efficiency.

A comparison study of sodium ion- and potassium ion-modified graphitic carbon nitride for photocatalytic hydrogen evolution.

It is well known that modifying graphitic carbon nitride (GCN) is an imperative strategy to improve its photocatalytic activity. In this study, Na-doped and K-doped graphitic carbon nitride (GCN-Na and GCN-K) were prepared via the simple thermal polymerization of a mixture of melamine and NaCl or KCl, respectively. The structure characterization showed that both Na+ and K+ intercalation could reduce the interlayer distance of GCN and introduce cyano defects in GCN, while K+ apparently had a stronger influence on the structure variation of GCN. The chemical composition data showed that both Na+ and K+ could easily interact with GCN, while K-doping caused a greater change in the C/N ratio than Na-doping. Moreover, compared to GCN-Na-5 (5 represents weight ratio of alkali halide to melamine), the conduction and valence bands of GCN-K-5 both shifted upward based on the electronic and optical measurements. Consequently, GCN-K-5 yielded an H2 evolution rate around 4 times higher than that of GCN-Na-5 under visible light irradiation (>420 nm). The cation size effect on GCN was proposed to be mainly responsible for the variation in the structure, optical and electronic properties of ion-doped GCNs, and hence the enhanced photocatalytic H2 evolution. The current work can provide new insight into optimizing photocatalysts for enhanced photocatalytic performances.

SPECTROSCOPY STUDY OF MCl2(H2O)n CLUSTER USING AB INITIO CALCULATIONS

The Infrared (IR) spectroscopy of alkali earth halide salt (MX2) complexes with few numbers of water molecules have been investigated for the first time in this work. BeCl2 and MgCl2 are divalent salts and have been incorporated with water as a polar solvent to form complexes of type MX2(H2O)n. The effect of ion size plays a critical rule in the interactions between solvent and solute. Therefore, Beryllium and Magnesium salts with chloride were chosen to explore this difference. The importance of BeCl2 and MgCl2 comes from their several applications in the industry and pharmacy. For instance, BeCl2 is widely used in the industry as a catalysis of Friede-Craft reactions, while the main application of MgCl2 in pharmacy is as hemodialysis and peritoneal dialysis fluids. Three complexes of each BeCl2 and MgCl2 with water, MX2(H2O)n (n=1-3), were studied, and the chemical structures of these complexes have been performed using ab initio calculations. Ab initio calculations were used to predict possible structures, isomers, and their corresponding IR spectra using Second-order Møller-Plesset perturbation theory (MP2) with 6-311++G as a basis sets. The Geometry evaluations, energy searches, vibrational frequency calculations, and the binding energy of each complex were also extracted theoretically. The minimum energy of complexes structures was calculated, and different isomers have been recorded. Ionic hydrogen bonds (IHBs) between the OH in each water molecule and the chloride ion in the MCl2 was proposed to be the main prevalent contribution to the binding between the salt and water. The bond length between the alkaline metal and chlorine showed a significant increase with increasing the attached water molecule as a result of forming the IHB. Also, the infrared vibrational bands of the OH stretching region were recorded for the minimum structures, and dramatic redshift was performed. The formation of contact-ion pair structures in which each solvent molecule forms an ionic hydrogen bond (IHB) to the salt ion-pair (X-M+X-) has been confirmed by the predicted infrared spectra.

Impact of finite ion size, Born energy difference and dielectric decrement on the electroosmosis of multivalent ionic mixtures in a nanotube

The electroosmotic flow (EOF) in a nanotube is analyzed by considering the finite ion size and dielectric decrement effects. The ion transport is governed by the modified Nernst-Planck equation, which takes into account the ion steric repulsion, Born energy difference, and dielectrophoretic force. The dielectric permittivity is considered to depend on the ionic concentration and ion size. The governing equations for fluid flow, ion transport, and electric field are solved numerically in their full form. The steric interaction is accounted, based on the Boublik–Mansoori–Carnahan–Starling–Leland (BMCSL) model, which considers the nonuniform ion size for monovalent as well as multivalent salts. We made a quantitative comparison with the standard PNP model for the lower range of charge density and highlighted the impact of ion size and dielectric decrement effects. For a highly charged surface, the impact due to finite ion size is non-negligible when the Debye length is in the order of the nanotube radius. However, the dielectric decrement is found to have a strong impact on a higher range of surface charge density or bulk ionic concentration. The EOF and the ion selectivity of the mixed electrolyte solution of different counterion size are considered in the present study. Present study provides an in-depth analysis of EOF through a cylindrical nanotube beyond the dilute solution and low charge density limits, which has not been addressed before.

Capacitive Behavior of Sodium Ion Pre-Intercalation Manganese Dioxide Supported on Titanium Nitride Substrate

The sodium ion pre-intercalation manganese dioxide (Na[Formula: see text]MnO[Formula: see text] is supported on titanium nitride (TiN) substrate to form electroactive Na[Formula: see text]MnO2/TiN electrode through an electrodeposition process in Mn(CH3COOH)2/Na2SO4 precursors with high Mn/Na ratio. MnO2 has a tiled leaf-like structure with a wrinkling morphology. Na[Formula: see text]MnO2 has a cross-linking nanorod structure with a nanoporous morphology, which is beneficial for electrolyte ion diffusion. The density functional theory (DFT) calculation results indicate that Na[Formula: see text]MnO2 reveals the enhanced density of states (DOS) and the lowered band gap than MnO2, which is consistent with higher cyclic voltammetry current response due to superior electroactivity of Na[Formula: see text]MnO2. The Faradaic process involves Na[Formula: see text] adsorption/desorption on the surface of MnO2 by contributing to electrochemical capacitance and Na[Formula: see text] intercalation/deintercalation on the deep interlayer of pre-intercalation Na[Formula: see text]MnO2 by contributing to pseudocapacitance. Concerning the electrolyte ion size effect, both MnO2/TiN and Na[Formula: see text]MnO2/TiN electrodes have higher capacitive performance in Li2SO4 electrolyte than that in Na2SO4 and K2SO4 electrolyte due to more feasible Li[Formula: see text] diffusion. When MnO2 is converted into Na[Formula: see text]MnO2, the capacitance at 2.5 mA cm[Formula: see text] increases from 351.3 mF cm[Formula: see text] to 405.6 mF cm[Formula: see text] in Na2SO4 electrolyte and from 376.3 mF cm[Formula: see text] to 465.1 mF cm[Formula: see text] in Li2SO4 electrolyte. The conductive TiN substrate leads to high rate capacity retention ratio of 50.7% for MnO2/TiN and 49.5% for Na[Formula: see text]MnO2/TiN when current density increases from 0.5 mA cm[Formula: see text] to 5 mA cm[Formula: see text]. So, Na[Formula: see text]MnO2/TiN with sodium ion pre-intercalation exhibits the improved capacitive performance in Li2SO4 electrolyte to act well as the promising supercapacitor electrode.

Influence of Ionic Strength on Hydrophobic Interactions in Water: Dependence on Solute Size and Shape.

Hydrophobicity is a phenomenon of great importance in biology, chemistry, and biochemistry. It is defined as the interaction between nonpolar molecules or groups in water and their low solubility. Hydrophobic interactions affect many processes in water, for example, complexation, surfactant aggregation, and coagulation. These interactions play a pivotal role in the formation and stability of proteins or biological membranes. In the present study, we assessed the effect of ionic strength, solute size, and shape on hydrophobic interactions between pairs of nonpolar particles. Pairs of methane, neopentane, adamantane, fullerene, ethane, propane, butane, hexane, octane, and decane were simulated by molecular dynamics in AMBER 16.0 force field. As a solvent, TIP3P and TIP4PEW water models were used. Potential of mean force (PMF) plots of these dimers were determined at four values of ionic strength, 0, 0.04, 0.08, and 0.40 mol/dm3, to observe its impact on hydrophobic interactions. The characteristic shape of PMFs with three extrema (contact minimum, solvent-separated minimum, and desolvation maximum) was observed for most of the compounds for hydrophobic interactions. Ionic strength affected hydrophobic interactions. We observed a tendency to deepen contact minima with an increase in ionic strength value in the case of spherical and spheroidal molecules. Additionally, two-dimensional distribution functions describing water density and average number of hydrogen bonds between water molecules were calculated in both water models for adamantane and hexane. It was observed that the density of water did not significantly change with the increase in ionic strength, but the average number of hydrogen bonds changed. The latter tendency strongly depends on the water model used for simulations.

Solubility of monoclinic and yttrium stabilized cubic ZrO2: Solution and surface thermodynamics guiding ultra-trace analytics in aqueous phase

The high stability of zirconium dioxide in aqueous environments is known and demonstrated, and this property is strongly used in nuclear industry to ensure the long term storage of wastes. However, only upper limits of its aqueous solubility are known reliably and lower limits linked to very well crystallized ZrO2 are much less assessed. Indeed, the low dissolution rate of zirconia makes the solubility measurements a challenging task. To overcome, high S/V ratios of nanoparticles zirconia were used. This work also improved the sensitivity of analytical techniques (HR ICP-MS) and methodologies, and a reliable experimental procedure was developed to measure zirconium (quantification limit ≈10−11 mol∙L−1). New Zr(IV) dioxide solubility data at pH between 0 and 2 were obtained approaching solubility from under-saturated conditions in (Na,H)Cl and (Na,H)ClO4 medium. Two crystalline nanoparticle structures were compared: monoclinic and yttrium stabilized cubic zirconia. Very low solubility was measured for monoclinic phase between pH 1.5 and 2: between (1.8±1.2) × 10−10 mol∙L−1 at pH 2 and (2.3±1.0) × 10−10 mol∙L−1 at pH 1.5. The cubic zirconia showed higher solubility. Integrating the effect of ionic strength, particle size and aqueous speciation, solubility constants of log Ks0 = (-8.43±0.69) for the monoclinic nanoparticles and log Ks0 = (-7.12±0.35) for the yttrium stabilized cubic nanoparticles were obtained. High-resolution techniques (HR-TEM, SAXS and STEM-HAADF) were also used to assess the evolution of morphology and surface before, during and at equilibrium. Analysis of these results shows that the morphology and surface of nanoparticles in the raw state and after reaching equilibrium in (Na,H)Cl and (Na,H)ClO4 medium are similar.

Effects of Ion Size and Dielectric Constant on Ion Transport and Transference Number in Polymer Electrolytes

Salt-doped polymers without added solvents have the potential to be nonflammable, robust electrolytes for batteries but suffer from low ion conductivity. Using bulky anions with delocalized charge may reduce ion agglomeration and increase conduction. However, size asymmetry between ions may increase preferential solvation of cations versus the larger anions, lowering the transference number t+ (fraction of conductivity contributed by the cation, relevant to battery performance). We use coarse-grained molecular dynamics simulations, including a 1/r4 potential to capture size-dependent solvation effects, to relate polymer and ion chemistry to t+ and overall conductivity. At low ion size disparity, increasing dielectric constant improves cation conduction due to the mitigation of ion aggregation and correlated cation–anion motion. However, at high ion size disparity, high dielectric medium results in strong preferential solvation of cations, reducing cation mobility and t+. The trade-off between better cation–anion separation and cation preferential solvation suggests that the strategy of developing high dielectric polymers may enhance performance only at low ion size disparity.

Influence of ion size effects on the electrokinetics of aqueous salt-free colloids in alternating electric fields.

Electrokinetics is the science of the physical phenomena appearing at the solid-liquid interface of dispersed particles subjected to external fields. Techniques based on electrokinetic phenomena constitute an important set of tools for the electrical characterization of colloids because of their sensitivity to the properties of particle-solution interfaces. Their rigorous description may require inclusion of the effects of finite size of chemical species in the theoretical models, and, particularly in the case of salt-free (no external salt added) aqueous colloids, also consideration of water dissociation and possible carbon dioxide contamination in the aqueous solution. A new ac electrokinetic model is presented for concentrated salt-free spherical colloids for arbitrary characteristics of the particles and aqueous solution, including finite-size effects of chemical species by appropriate modifications of the chemical reaction equations to include such non-ideal aspects. The numerical solution of the electrokinetic equations in an alternating electric field has also been carried out by using a realistic non-equilibrium scenario accounting for association-dissociation processes in the chemical reactions. The results demonstrate the importance of including finite-size effects in the electrokinetic response of the colloid, mainly at high frequencies of the electric field, and for highly charged colloids. Findings of previous models for pointlike ions or for ideal salt-free colloids including finite ion size effects are recovered with the present model, for the appropriate limiting conditions.