Ion Charge Density Research Articles

Transient response of an electrolyte to a thermal quench.

We study the transient response of an electrolytic cell subject to a small, suddenly applied temperature increase at one of its two bounding electrode surfaces. An inhomogeneous temperature profile then develops, causing, via the Soret effect, ionic rearrangements towards a state of polarized ionic charge density q and local salt density c. For the case of equal cationic and anionic diffusivities, we derive analytical approximations to q,c, and the thermovoltage V_{T} for early (t≪τ_{T}) and late (t≫τ_{T}) times as compared to the relaxation time τ_{T} of the temperature. We challenge the conventional wisdom that the typically large Lewis number, the ratio a/D of thermal to ionic diffusivities, of most liquids implies a quickly reached steady-state temperature profile onto which ions relax slowly. Though true for the evolution of c, it turns out that q (and V_{T}) can respond much faster. Particularly when the cell is much bigger than the Debye length, a significant portion of the transient response of the cell falls in the t≪τ_{T} regime, for which our approximated q (corroborated by numerics) exhibits a density wave that has not been discussed before in this context. For electrolytes with unequal ionic diffusivities, V_{T} exhibits a two-step relaxation process, in agreement with experimental data of Bonetti etal. [J. Chem. Phys. 142, 244708 (2015)JCPSA60021-960610.1063/1.4923199].

Signal transmission through elements of the cytoskeleton form an optimized information network in eukaryotic cells

Multiple prior empirical and theoretical studies have demonstrated wire-like flow of electrons and ions along elements of the cytoskeleton but this has never been linked to a biological function. Here we propose that eukaryotes use this mode of signal transmission to convey spatial and temporal environmental information from the cell membrane to the nucleus. The cell membrane, as the interface between intra- and extra-cellular environments, is the site at which much external information is received. Prior studies have demonstrated that transmembrane ion gradients permit information acquisition when an environmental signal interacts with specialized protein gates in membrane ion channels and producing specific ions to flow into or out of the cell along concentration gradients. The resulting localized change in cytoplasmic ion concentrations and charge density can alter location and enzymatic function of peripheral membrane proteins. This allows the cell to process the information and rapidly deploy a local response. Here we investigate transmission of information received and processed in and around the cell membrane by elements of the cytoskeleton to the nucleus to alter gene expression. We demonstrate signal transmission by ion flow along the cytoskeleton is highly optimized. In particular, microtubules, with diameters of about 30 nm, carry coarse-grained Shannon information to the centrosome adjacent to the nucleus with minimum loss of input source information. And, microfilaments, with diameters of about 4 nm, transmit maximum Fisher (fine-grained) information to protein complexes in the nuclear membrane. These previously unrecognized information dynamics allow continuous integration of spatial and temporal environmental signals with inherited information in the genome.

Insights into the role of ionic wind in honeycomb electrostatic precipitators

Electrostatic precipitators (ESPs) separate particles from flue gas by corona discharge and accompany by the generation of ionic wind. In this work, a Computational Fluid Dynamics model was presented to investigate the effects of ionic wind on flow field and particle precipitation in a honeycomb ESP in terms of the coupled processes among corona discharge, gas flow, particle charging and transport. Results indicated that the electric field and ion charge density around the needle tips were highest and respectively reach 2.5 × 106 V/m and 0.164 C/m3 in the gas without suspended particles, which played a key role in corona-electrostatic field. The maximum velocity of ionic wind could reach 13.81, 11.74 and 9.42 m/s under the applied voltage of 27, 21 and 15 kV, and ionic wind velocity sharply decreased away from the needle tip. Meanwhile, the flow field could be divided into three regions (ionic wind affected region, vortex and back flow region) according to the direction of gas flow velocity. When the electrically neutral particles with a spherical shape were injected into ESP at the entrance, the charged particles were transported by drag force and electric force, and inhomogeneous distribution of the deposited particle has occurred because of ionic wind. More intense vortices were formed with the increase in applied voltage, and promoting the particle precipitation process. Moreover, higher applied voltage enhanced the aggregation of particles in the upstream, and reduced the dead zone of deposited particles in the downstream.

In Situ Liquid Secondary Ion Mass Spectrometry: A Surprisingly Soft Ionization Process for Investigation of Halide Ion Hydration.

The understanding of ion solvation phenomena is of significance due to their influences on many important chemical, biological, and environmental processes. Mass spectrometry (MS)-based methods have been used to investigate this topic with molecular insights. As ion-solvent interactions are weak, ionization processes should be as soft as possible in order to retain solvation structures. An in situ liquid secondary ion MS (SIMS) approach developed in our group has been recently utilized in investigations of Li ion solvation in nonaqueous solution, and it detected a series of solvated Li ions. As traditionally SIMS has long been recognized as a hard ionization process with strong damage occurring at the sputtering interface, it is very interesting to study further how soft in situ liquid SIMS can be. In this work, we used halide ion hydration as an example to compare the ionization performance of the in situ liquid SIMS approach with regular electrospray ionization MS (ESI-MS). Results show that, although ESI has been recognized as a soft ionization method, nearly no solvated halide ions were detected by ESI-MS analysis, which acquired only strong signals of salt ion clusters. In contrast, in liquid SIMS spectra, a series of obvious hydrated halide ion compositions could be observed. We further evaluated the hydration numbers of halide ions and revealed the effects of the ion size, charge density, and polarizability on the hydration phenomenon. Our findings demonstrated that the in situ liquid SIMS approach is surprisingly soft, and it is expected to have very broad applications on investigation of various ion-solvent interactions and many other interesting chemical processes (e.g., the initial nucleation of nanoparticle formation) in liquid environment.

Acceleration of carbon ions to high energies by a multi-PW laser

Extreme Light Infrastructure (ELI) is a large-scale European project, still in the development stage, offering parameters of laser drivers required for multiple applications (femtosecond pulse duration, ultra-relativistic laser intensities ∼ 1022 - 1023 W/cm2), however studies of ion acceleration in the given intensity regime are still in the very early stages and require a deeper understanding of the processes occurring during laser-matter interactions to maximize the efficiency of ion acceleration. The purpose of this work is a numerical examination of the properties of carbon ion beams produced during the interaction of an ultra-intense laser beams (of intensities ∼ 1021 – 1023 W/cm2 and pulse duration order of femtoseconds, predicted to be available at ELI-NP, Romania) with C12 target. The dependence of ion beam parameters, such as intensity, energy spectrum, maximum and average ion energy and spatial distribution of ion charge density, on laser pulse parameters (mainly intensity) and the target thickness is investigated. The possibility of generation of high intensity, GeV energy ion beams in the foregoing conditions is demonstrated. The obtained results can be useful for research in high energy-density physics, nuclear physics or medical applications of ion beams.

Dynamics of the ions emitted in backward and forward direction during laser ablation of thin Sn film

Laser-generated ions emitted in backward and forward directions from an 80 nm thick Sn film deposited on the soda lime glass were investigated in the range of laser fluence (93–521 J/cm2). The ion collectors operating in time-of-flight configuration were employed to measure charge density and energy of the Sn ions emitted in both directions. As expected, the charge density and peak energy of the ions emitted in backward direction were found to increase with the laser fluence: the ion charge density and peak ion energy increased by a factor of three and ten, respectively. In contrast, the charge density of the ions emitted in forward direction decreased and their energy did not seem to vary with laser fluence. The surface morphology of the beam spot at the film and substrate was examined with the help of an optical microscope. The heat conduction equation is numerically solved to simulate the temporal distribution of temperature at the surface and along depth of the Sn film. A model, based on the results of optical microscopy and computer simulation, is proposed to explain the peculiar behaviour of the charge density and energy of the ions emitted in forward direction.

Ab initio molecular dynamics studies of hydroxide coordination of alkaline earth metals and uranyl.

Ab initio molecular dynamics (AIMD) simulations of the Mg2+, Ca2+, Sr2+ and UO22+ ions in either a pure aqueous environment or an environment containing two hydroxide ions have been carried out at the density functional level of theory, employing the generalised gradient approximation via the PBE exchange-correlation functional. Calculated mean M-O bond lengths in the first solvation shell of the aquo systems compared very well to existing experimental and computational literature, with bond lengths well within values measured previously and coordination numbers in line with previously calculated values. When applied to systems containing additional hydroxide ions, the methodology revealed increased bond lengths in all systems. Proton transfer events (PTEs) were recorded and were found to be most prevalent in the strontium hydroxide systems, likely due to the low charge density of the ion and the consequent lack of hydroxide coordination. For all alkaline earths, intrashell PTEs which occurred outside of the first solvation shell were most prevalent. Only three PTEs were identified in the entire simulation data of the uranium dihydroxide system, indicating the clear impact of the increased charge density of the hexavalent uranium ion on the strength of metal-oxygen bonds in aqueous solution. Broadly, systems containing more charge dense ions were found to exhibit fewer PTEs than those containing ions of lower charge density.

Physicochemical interactions of organic acids influencing microstructure and permselectivity of anion exchange membrane

Permselectivity and water uptake behaviors of anion exchange membrane (AEM) were investigated with organic acids. Contribution of the number of carboxyl group (acetic acid: AA, malic acid: MA, citric acid: CA) and hydrocarbon chain lengths (formic acid: FA, AA, propionic acid: PA and n-butyric acid: BA) in water uptake and permselectivity values were separately investigated with five different concentrations 0.025, 0.05, 0.075, 0.1 and 0.125 mol·L−1 of each acid at two different pH 2.0 and 7.5 conditions. Microstructural changes occurring due to interaction of carboxylate anion and NR4+ groups of AEM resulted in permselectivity behavior. Permselectivity trend: CA < MA < AA could be explained by counter-ion condensation resulting out of strong counter-ion interactions with AEM fixed charges. Co-ion mobility values could explain variation in permselectivity at pH 2.0 and 7.5. While, water uptake and ionic size were dominant factors to explain the permselectivity trend: FA > AA > PA > BA. Complex nature of interactions due to properties (size, charge, ionic charge density, mobility, diffusivity, stokes radius etc.) of carboxylate anions were explained using diffusivity ratio (counter/co-ion, D2/D1), adsorption equilibrium and fraction of dissociated species.

A critical review of the application of chelating agents to enable Fenton and Fenton-like reactions at high pH values

To overcome the drawback of low pH requirement of the classical Fenton reaction, researchers have applied chelating agents to form complexes with Fe and enable Fenton reaction at high pHs, which is reviewed in this article. The chelating agents reviewed include humic substances, polycarboxylates, aminopolycarboxylic acids, and polyoxometalates. Ligands affect the reactivity of Fe-complexes by changing their redox potentials, promoting their reaction with H2O2, and competing with target contaminants for the oxidative species. Fe(III)-complexes are reduced to Fe(II)-complexes by O2- not H2O2, as indicated by their redox potentials. The stability constants of Fe-complexes increase with increasing pKa values of the corresponding ligands and also with increasing charge density of the metal ions. A higher stability constant of Fe(III)-complex indicates higher reaction rate of corresponding Fe(II)-complex with H2O2 and lower reduction rate of Fe(III)-complex to Fe(II)-complex. OH, O2-, and ferryl species were reported to be the reactive species on the contaminant removal in the chelate-modified Fenton process. The generation of these species depends on the chelating agents and reaction conditions. The process is very efficient in degrading contaminants, indicating a potential treatment approach for the pollution remediation at natural pH.

Replacement Times of a Spectrum of Elements in the North Atlantic Based on Thorium Supply

AbstractThe measurable supply of 232Th to the ocean can be used to derive the supply of other elements, which is more difficult to quantify directly. The measured inventory of an element divided by the derived supply yields a replacement time estimate, which in special circumstances is related to a residence time. As a proof of concept, Th‐based supply rates imply a range in the replacement times of the rare earth elements in the North Atlantic that is consistent with the chemical reactivity of rare earth elements related to their ionic charge density. Similar estimates of replacement times for the bioactive trace elements (Fe, Mn, Zn, Cd, Cu, and Co), ranging from &lt;5 years to &gt;50,000 years, demonstrate the broad range of elemental reactivity in the ocean. Here we discuss how variations in source composition, fractional solubility ratios, or noncontinental sources, such as hydrothermal vents, lead to uncertainties in Th‐based replacement time estimates. We show that the constraints on oceanic replacement time provided by the Th‐based calculations are broadly applicable in predicting how elements are distributed in the ocean and for some elements, such as Fe, may inform us on how the carbon cycle may be impacted by trace element supply and removal.

Analytical model of electro-hydrodynamic flow in corona discharge.

We present an analytical model for electro-hydrodynamic flow that describes the relationship between the corona voltage, electric field, and ion charge density. The interaction between the accelerated ions and the neutral gas molecules is modeled as an external body force in the Navier-Stokes equation. The gas flow characteristics are solved from conservation principles with spectral methods. This multiphysics model is shown to match experimental data for a point-to-ring corona configuration, shedding new insights into mass, charge, and momentum transport phenomena, and can be readily implemented in any numerical simulation.

Two new alkaline earth metal organic frameworks with the diamino derivative of biphenyl-4,4′-dicarboxylate as bridging ligand: Structures, fluorescence and quenching by gas phase aldehydes

Alkaline earth metal ion organic frameworks (AEMOFs) represent a relatively underexplored subcategory of MOFs. Two new MOFs [Ca6(bpdc-(NH2)2)5(μ3-HCO2)2(H2O)2.5(DMF)0.5]·0.5H2O·2.5DMF (1) and [Sr4(bpdc-(NH2)4)(μ2-DMF)2(DMF)1/3]·2/3(DMF) (2) [H2bpdc-(NH2)2 = 2,2′-diamino-[1,1′-biphenyl]-4,4′-dicarboxylic acid); DMF = N,N-dimethylformamide] are presented here. These MOFs display structural variety with diverse topologies and new structural features. Luminescence studies revealed that both MOFs display ligand based fluorescence with small differences in emission profiles possibly attributable to the difference in charge density of the metal ions combined with the different conformation adopted by the ligand in the crystal structures of 1 and 2. Furthermore, initial sensing studies reveal that both MOFs can potentially function as fluorescent sensors for gas phase aldehydes.

Transient dynamics of electric double-layer capacitors: Exact expressions within the Debye-Falkenhagen approximation.

We revisit a classical problem of theoretical electrochemistry: the response of an electric double-layer capacitor (EDLC) subject to a small, suddenly applied external potential. We solve the Debye-Falkenhagen equation to obtain exact expressions for key EDLC quantities: the ionic charge density, the ionic current density, and the electric field. In contrast to earlier works, our results are not restricted to the long-time asymptotics of those quantities. The solutions take the form of infinite sums whose successive terms all decay exponentially with increasingly short relaxation times. Importantly, this set of relaxation times is the same among all aforementioned EDLC quantities; this property is demanded on physical grounds but not generally achieved within approximation schemes. The scaling of the largest relaxation timescale τ_{1}, that determines the long-time decay, is in accordance with earlier results: Depending on the Debye length, λ_{D}, and the electrode separation, 2L, it amounts to τ_{1}≃λ_{D}L/D for L≫λ_{D} and τ_{1}≃4L^{2}/(π^{2}D) for L≪λ_{D}, respectively (with D being the ionic diffusivity).

On the dispersion decay for crystals in the linearized Schrödinger–Poisson model

The Schrödinger–Poisson–Newton equations for crystals with a cubic lattice and one ion per cell are considered. The ion charge density is assumed i) to satisfy the Wiener and Jellium conditions introduced in our previous paper [25], and ii) to be exponentially decaying at infinity. The corresponding examples are given. We study the linearized dynamics at the ground state. The dispersion relations are introduced via spectral resolution for the non-selfadjoint Hamilton generator using the positivity of the energy established in [25]. Our main result is the dispersion decay in the weighted Sobolev norms for solutions with initial states from the space of continuous spectrum of the Hamilton generator. We also prove the absence of singular spectrum and limiting absorption principle. The multiplicity of every eigenvalue is shown to be infinite. The proofs rely on novel exact bounds and compactness for the inversion of the Bloch generators and on uniform asymptotics for the dispersion relations. We derive the bounds by the energy positivity from [25]. We also use the theory of analytic sets.

Vesicle Adhesion and Fusion Studied by Small-Angle X-Ray Scattering

We have studied the adhesion state (also denoted by docking state) of lipid vesicles as induced by the divalent ions Ca2+ or Mg2+ at well-controlled ion concentration, lipid composition, and charge density. The bilayer structure and the interbilayer distance in the docking state were analyzed by small-angle x-ray scattering. A strong adhesion state was observed for DOPC:DOPS vesicles, indicating like-charge attraction resulting from ion correlations. The observed interbilayer separations of ∼1.6 nm agree quantitatively with the predictions of electrostatics in the strong coupling regime. Although this phenomenon was observed when mixing anionic and zwitterionic (or neutral) lipids, pure anionic membranes (DOPS) with highest charge density σ resulted in a direct phase transition to a multilamellar state, which must be accompanied by rupture and fusion of vesicles. To extend the structural assay toward protein-controlled docking and fusion, we have characterized reconstituted N-ethylmaleimide-sensitive factor attachment protein receptors in controlled proteoliposome suspensions by small-angle x-ray scattering.

Response of carbon and tungsten surfaces to hydrogen plasma of different temperatures

The basic understanding of the interaction between energetic hydrogen plasma with carbon and tungsten based surfaces is crucially important for analyzing plasma-wall interaction in divertors of fusion devices and other plasma applications. The ion reflection coefficient, ion absorption coefficient, total ion charge density, and ion density distribution have been studied using a kinetic trajectory simulation model at different ion temperatures. It has been observed that the ion reflection coefficient and the ion absorption coefficient of the incident particles depend on kinetic energy: higher energy ions are less likely to be reflected as they have enough energy to bury themselves within the solid.

Effect of electrolytes on electrokinetics and flocculation behavior of bentonite-polyacrylamide dispersions

Abstract In this study, the influence of electrolytes on bentonite dispersions flocculated with different polyacrylamides varying in charge type, density and molecular weights has been investigated. The presence of electrolytes was found to induce profound impact on the flocculation behavior of bentonite-polyacrylamide dispersions, which was analyzed by means of residual turbidity, zeta potential and floc size distribution tests. Electrolytes enhanced the adsorption of anionic polyacrylamide chains on negative bentonite surface, while hindering adsorption of cationic polyacrylamides. Electric double layer compression and mediated flocculation by metal cations were the principle mechanisms involved in the improvement of flocculation behavior. High molecular weight and charge density variants greatly reduced the turbidity and negative zeta potential of dispersions for anionic polyacrylamides. Furthermore, charge density of metal ions was found to be a determining factor. Divalent salts were more efficient for flocculating dispersions using anionic polyacrylamides, while monovalent salts were preferable for cationic polyacrylamides owing to electrostatic repulsions. Amphoteric polyacrylamides displayed similar results based on their anionic/cationic nature. Similar observations were recorded for floc size measurements. High charge density variants of anionic polyacrylamides in the presence of divalent salts like CaCl2 produced large flocs. On the other hand, no significant changes in floc sizes were observed for cationic polyacrylamides in the presence of salts. Overall, this study successfully determines the effect of electrolytes on the flocculation behavior of bentonite dispersions.

Role of Ionic Charge Density in Donnan Exclusion of Monovalent Anions by Nanofiltration.

The main objective of this study is to examine how the charge densities of four monovalent anions-fluoride (F-), chloride (Cl-), bromide (Br-), and nitrate (NO3-)-influence their Donnan (charge) exclusion by a charged nanofiltration (NF) membrane. We systematically studied the rejection behavior of ternary ion solutions containing sodium cation (Na+) and two of the monovalent anions as a function of the pH with a polyamide NF membrane. In the solutions containing F- and Cl- or F- and Br-, F- rejection was higher than Cl- or Br- rejection only when the solution pH was higher than 5.5, suggesting that F- (which has a higher charge density) was repelled more strongly by the negatively charged membrane. The order of change in the activation energy for the transport of the four anions through the polyamide membrane as a response to the increase of the membrane negative charge was the following: F- > Cl- > NO3- > Br-. This order corroborates our main hypothesis that an anion with a smaller ionic radius, and hence a higher charge density, is more affected by the Donnan (charge)-exclusion mechanism in NF. We conclude with a proposed mechanism for the role of ionic charge density in the rejection of monovalent anions in NF.

Numerical simulation of corona discharge and particle transport behavior with the particle space charge effect

The corona discharge characteristics of an electrostatic precipitator are an important factor that affects particle charging and collection. The electrical characteristics of a wire-plate electrostatic precipitator and the particle transport behavior were studied by considering the electrohydrodynamics (EHD) and the effect of particle space charge through numerical simulation. Simulation results showed that the effect of particle space charge intensifies in extremely small particles, such as submicron particles. This condition significantly influences electric field, ionic charge density, and current. The electric field intensity and ionic charge concentration significantly decreased. The reduction in the minimum field intensity between the electrodes decreased to 50%, and the lowest concentration of the ionic charge tended to 0 when the particle size varied from 5µm to 0.1µm. When the applied voltage increased from 13kV to 40kV, the space charge ratio of the particles larger than 2µm was reduced to almost 0 but remained at a high level for the particles less than 0.5µm whose corresponding current was lower by 20% than that without particle condition. The ionic wind in the electrostatic field also weakened because the movement of ions was restricted for corona suppression, leading to decreased corona current. Furthermore, the particle transport behavior was compared considering the effect of particle space charge. Results indicated that the difference between the two conditions increased from 1.3% to 47.4% with decreasing particle size from 5µm to 0.07µm. In addition, the particle migration velocity of the 0.1µm particles increased by 9.8%, from 0.2 to 0.1µm, even if the drag force was reduced when considering the particle space charge. A modified I–V equation was provided, with fitting coefficient of 0.996, and is thus worthy of reference in practical application.

Effect of ion size and charge density on the electrochemical characteristics of α-MoO3 using aqueous Be2+ and Mg2+ sulfate electrolytes

We investigated the electrochemical characteristics of layer structured α-MoO3 using two divalent ions (Mg2+ and Be2+) of different sizes. The cyclic voltammetry studies showed a high specific capacity with Be2+ electrolyte, and galvanostatic intermittent titration (GITT) measurements revealed a higher diffusion coefficient for Be2+ in MoO3 despite having a higher charge density than Mg2+. The intercalation of both ions resulted in poor cyclability, but a slightly better performance with Be2+ electrolyte could be attributed to favored diffusion of Be2+ in MoO3 due to its covalent nature as well as preferred coordination number.