Mobile Ion Concentration Research Articles

Na+Ion Conducting Hot-pressed Nano Composite Polymer Electrolytes

Synthesis, characterization and polymeric battery studies of Na + ion conducting NanoComposite Polymer Electrolyte (NCPE) membranes: (1-x) [75PEO: 25NaPO 3]: x SiO 2, where x = 0 - 15 wt. (%), has been reported. NCPE membranes have been casted using a novel hot-press technique in place of the traditional solution cast method. The dispersal of SiO 2 in SPE host: (75PEO: 25NaPO 3), a conductivity enhancement of an order of magnitude achieved in NCPE film: [93 (75PEO: 25NaPO 3): 7 SiO 2]. This has been referred to as Optimum Conducting Composition (OCC). Material characterizations have been done with the help of XRD, SEM and DSC techniques. The ion transport behaviour in hot-pressed NCPEs has been discussed on the basis of experimental measurements on some basic ionic parameters viz. conductivity ( �), ionic mobility ( μ), mobile ion concentration (n) and ionic transference number (t ion ). The temperature dependent conductivity studies have been done to compute the activation energy (E a) values from the ‘log σ – 1/T’ Arrhenius plots. The ion conducting solid state polymeric battery was fabricated and cell-potential discharge characteristics have been studied at different load conditions .

Hot-pressed Ag+Ion Conducting Glass-Polymer Electrolytes: Synthesis and Battery Application

Synthesis of new Ag + ion conducting glass-polymer electrolytes (GPEs): (1-x) PEO: x [0.75(0.75AgI:0.25AgCl):0.25(Ag 2O:P 2O5)], where 0 < x < 50 wt. (%), are reported. GPEs have been casted using hot-press techniques. The highest conducting composition 70PEO: 30[0.75(0.75AgI:0.25AgCl):0.25(Ag 2O:P 2O5)], with conductivity ( �) ~ 6.0 × 10 -6 S.cm -1 , was identified from the compositional dependent conductivity studies and this has been referred to as the Optimum Conducting Composition (OCC). Approximately three orders of conductivity enhancement have been achieved in GPE OCC from that of the pure polymer PEO. The glass-polymer complexation has been confirmed by SEM and DSC analysis. Ion transport parameters viz. ionic conductivity (�), ionic mobility ( µ), mobile ion concentration (n) and ionic transference number (t ion ) have been characterized using different experimental techniques. Solid-state polymeric batteries were fabricated using GPE OCC as electrolyte and the cell-potential discharge characteristics were studied under different load conditions at room temperature.

Do monovalent mobile ions affect DNA's flexibility at high salt content?

Numerous theoretical and experimental studies disagree on the impact of surrounding mobile ions on DNA conformational flexibility at high salt content. Specifically, it is not clear how the DNA persistence length varies when concentration of monovalent mobile ions is increased beyond the physiological value of ∼0.1 M. In the present Communication we address this biologically important issue computationally by means of molecular dynamics simulations. We utilize our recently developed chemically accurate coarse-grained model for the double-stranded DNA with explicit mobile ions. We find that in a range of moderate-to-high ionic concentrations, ∼0.1-1 M, DNA persistence length drops noticeably by ∼25%. Our results contradict some experimental works and the celebrated theory of Odijk, Skolnick and Fixman (Skolnick et al., Macromolecules, 1977, 10, 944), suggesting a negligible variation of DNA persistence length at these concentrations. On the other hand, our findings are in near quantitative agreement with a number of other theoretical and experimental studies. Combined with our recent work on elucidating the role of elastic and electrostatic effects in maintaining DNA shape, the results reported here may indicate that conceptually new understanding of DNA rigidity needs to be developed.

Electrical transport behaviour of bio-polymer electrolyte system: Potato starch+ammonium iodide

A new bio-polymer electrolyte system is prepared by mixing NH4I with potato starch. Prepared material is an ionic conductor having ionic transference number (tion) ∼0.95 and ambient electrical conductivity ∼2.4 × 10−4 S/cm. Relation between the conductivity trend, mobile ion concentration factor (K) and mobility factor (μf) with respect to salt concentration and temperature, is established. The optical micrograph of starch + NH4I system indicated typical starch–iodine relationship in acidic medium. In conductivity formulism three different regions for power law exponent (n) having values between 0 < n < 2 is found. The regions are associated with dc conductivity, NCL and superlinear like behaviour. In starch electrolyte, NCL region is obtained at room temperature and low frequency region. Material is humidity immune up to 77% relative humidity and a very small variation with temperature has been found hence results are encouraging for possible use of starch based electrolytes in humidity immune devices.

Proton conduction in the binary system (1 − x)CsHSeO4–xKHSeO4 studied with a free-energy model

Electrical Impedance Spectroscopy (EIS) was used to study the electrical properties of the (1 − x)CsHSeO4–xKHSeO4 binary system with concentrations x = 0.0 and 0.1. The results show a higher proton-conduction phase above 80°C for both concentrations, however, while DC conductivity of CsHSeO4 shows a gradual change to higher values in the 80–118°C temperature range, the 0.9CsHSeO4–0.1KHSeO4 concentration reveals an abrupt change at about 80°C to an intermediate temperature phase. The observed behavior for the doped sample was modeled using a trial free-energy density, based on the concentration of mobile ions, that takes into account the formation of defects, configurational and phonon entropies, and defect-defect interactions. By minimising the free-energy density one obtains two roots for the carrier concentration at a given temperature, which corresponds to a stable and metastable configuration. It is possible to characterise the phase behavior of the system by means of temperature and two model parameters, which depend on the crystalline properties of the system, but not on temperature. One can successfully explain the conductivity behavior of the system by changing the model parameters if it is assumed that its variations are due to the carriers density.

Study of ion transport behavior in a mechanochemically synthesized silver halide mixed composite system: [0.75 AgI:0.25 AgCl

Ion transport behavior in a mechanochemically synthesized silver halide mixed composite has been investigated. AgI and AgCl, in 75: 25 mol. wt. (%) ratio, has been prepared by high energy ball milling for different milling times viz. 5, 10, 20, 30, 40, and 50 h as well as by simple physical mixing (referred to as zero hour milling). The room temperature conductivity has been evaluated as a function of milling time. The conductivity increased initially with increasing milling time, then decreased. The increase in conductivity has been attributed to the increased degree of amorphosity in the sample as a consequence of high energy ball milling. The 30-hour milled sample exhibited highest conductivity with an enhancement of more an order of magnitude from that of zero hour milled sample. To explain the ion transport mechanism in the optimum conducting sample, other basic ionic parameters viz. ionic mobility (μ), mobile ion concentration (n), ionic transference number (t ion) etc. have also been determined. The materials and structural properties have been characterized using XRD, FTIR, and DSC techniques. Using the optimum conducting sample as electrolyte, all-solid-state battery has been fabricated having cell configuration: Ag (anode) // (0.75 AgI:0.25AgCl) // C + I 2 + Electrolyte (cathode), and the cell performance has been studied under varying load conditions.

Oxygen surface exchange and diffusion studies of La 2Mo 2O 9 in different exchange atmospheres

A combination of 18O tracer isotopic exchange and Secondary Ion Mass Spectrometry (SIMS) measurements was applied to obtain oxygen surface exchange and diffusion coefficients of La 2Mo 2O 9. The isotopic exchange was conducted in dry ( 18O 2) and wet (H 2 18O) exchange atmospheres respectively with the advantages and disadvantages of each exchange discussed. A decrease in the oxygen diffusion coefficients was observed for the wet exchange method which was accompanied by an increase in the oxygen diffusion activation energy, indicating that the humidified and dry atmospheres affect the oxygen transport differently. Changes in the surface exchange coefficients at the phase transition temperature were observed suggesting a different rate-limiting step in the oxygen exchange and diffusion processes. The oxygen diffusivity was correlated to the ionic conductivity using the Nernst–Einstein relation from which the concentration of mobile oxygen ions was estimated to be 5 per unit cell. The result is consistent for both the calculated conductivity from diffusion coefficients and the measured values from the AC impedance spectroscopy.

Phase field model simulations of hydrogel dynamics under chemical stimulation

Two decades ago, it has been observed experimentally that hydrogels immersed in a bath solution swells or shrinks under external stimulations (Ricka et al., Macromolecules 17:2916–2921, 1984). Recently, this fact has received renewed interest, since understanding the precise mechanisms underlying that kind of behavior has the potential to tailor most sensitive drug delivery systems based on hydrogels (Segalman and Witkowski, Mater Sci Eng C 2:243–249, 1995). Here we contribute to a precise understanding of the mechanisms responsible for the hydrogels’ swelling kinetics as well as dynamics by proposing for the first time a model approach that can resolve the inherent short-range correlation effects along the hydrogel–solution interface jointly with the long-range ionic transport fields. To that end, we investigate the swelling dynamics of hydrogels, which is a moving boundary problem, by a phase field model, which couples the Nernst–Planck equation for the concentration of mobile ions, Poisson equation for the electric potential, mechanical equation for the displacement, and an equation for the phase field variable. Simulation for two-dimensional case reveals that under the chemical stimulation, the hydrogel will swell or shrink if the concentration of mobile ions inside bath solution decreases or increases. This is in agreement with the experimental results qualitatively and validates our new model approach.

Charge dynamics and bending actuation in Aquivion membrane swelled with ionic liquids

The actuation strain and speed of ionic electroactive polymer (EAP) actuators are mainly determined by the charge transport through the actuators and excess ion storage near the electrodes. We employ a recently developed theory on ion transport and storage to investigate the charge dynamics of short side chain Aquivion® (Hyflon®) membranes with different uptakes of ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). The results reveal the existence of a critical uptake of ionic liquids above which the membrane exhibits a high ionic conductivity (σ > 5×10−2 mS/cm). Especially, we investigate the charge dynamics under voltages which are in the range for practical device operation (∼1 V and higher). The results show that the ionic conductivity, ionic mobility, and mobile ion concentration do not change with the applied voltage below 1 V (and for σ below 4 V). The results also show that bending actuation of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chains improve the electromechanical coupling between the excess ions and the membrane backbones, while not affecting the actuation speed.

Effect of ethylene carbonate in poly (methyl methacrylate)-lithium tetraborate based polymer electrolytes

Thin films composed of poly (methyl methacrylate) (PMMA), lithium tetraborate (Li 2B 4O 7) and ethylene carbonate (EC) were prepared by solution casting method. The highest ionic conductivity at room temperature was achieved for the composition PMMA:Li 2B 4O 7:EC (42:18:40) with the value 1.29 × 10 −5 S cm −1. The presence of plasticizer in the polymer complex is crucial in improving the ionic conductivity by increasing the concentration of free mobile ions through the structural conversion from crystalline to amorphous phase. This conversion lowers the viscosity of the polymer complex. Conductivity–temperature plots were found to obey Williams–Landel–Ferry (WLF) mechanism. Dielectric data was analyzed using the dielectric permittivity ( ε′) and dielectric modulus ( M′) of the samples. Fourier transform infrared (FTIR) studies confirmed that complexation occurs between PMMA, Li 2B 4O 7 and EC. Thermal stability of the polymer complex, which decreases with the addition of plasticizer (EC), was determined using thermal gravimetric analysis (TGA).

Materials and ion transport property studies on hot-press casted solid polymer electrolyte membranes: [(1 − x) PEO: x KIO 3

Materials and ion transport property characterization in Solid Polymer Electrolyte (SPE) membranes: (1 − x) PEO: x KIO 3, where x = 0, 10, 20, 30, 40, 50 wt.%, have been studied. SPE films have been prepared following two casting techniques: a novel hot-press (extrusion) and the traditional solution cast. Hot-press technique is a completely dry/solvent free/rapid/inexpensive procedure as compared to solution cast method and has recently been receiving wider acceptability to cast membranes of ion conducting polymeric electrolytes. ‘Log σ − x’ study revealed σ-maxima at salt concentration x = 30 wt.% for SPE film prepared by both the methods. However, hot-pressed SPE film: 70 PEO: 30 KIO 3 exhibited relatively higher room temperature conductivity ( σ ∼ 4.40 × 10 − 7 S cm − 1 ) than that of the solution casted film. This has been referred to as Optimum Conducting Composition (OCC) SPE film. Materials characterization in OCC SPE film has been done by XRD, FTIR and DSC techniques. These studies confirmed the complexation of salt in the polymeric host. Some basic ionic parameters viz. conductivity ( σ), ionic mobility (μ), mobile ion concentration (n), ionic transference number (t ion) have been determined using different experimental procedures to understand the ion transport behaviour in OCC SPE material. The temperature dependent conductivity measurement has also been carried out and the activation energy (E a) has been computed from the linear least square fitting of ‘log σ − 1 / T’ Arrhenius plot.

Hot-pressed Na+ion conducting solid polymer electrolytes: (1 - x) PEO: x NaPO3

Synthesis and ion transport property studies on hot-pressed Na+ ion conducting solid polymer electrolytes (SPEs): (1-x) PEO: x NaPO3, where x in wt.%, are reported. The compositional dependent conductivity (σ) studies revealed SPE film: (75PEO: 25NaPO3) as the optimum conducting composition (OCC) with room temperature conductivity σ ~ 6.7 × 10-7 S cm-1, which is more than two orders of magnitude higher than that of pure PEO polymer host (σ ~ 3.2 × 10-9 S cm-1). Materials characterization and polymer-salt complexation were done with the help of XRD, FTIR, SEM, DSC techniques. In order to understand the ion transport behaviour in SPEs, the measurement on some basic ionic parameters viz. ionic conductivity (σ), ionic mobility (μ), mobile ion concentration (n), ionic transference number (tion) have been carried out using different experimental techniques. The activation energy (Ea) values involved in the thermally activated conductivity processes have been computed from “log σ - 1/T” Arrhenius plots.

Quantifying the Drivers of the Increasing Colored Organic Matter in Boreal Surface Waters

Long-term monitoring of surface water quality has shown increasing concentrations of colored dissolved organic matter (CDOM) across large parts of the northern latitudes. This has increased purification costs for domestic water works. Appropriate abatement actions require better knowledge of the governing factors for the increase, and this has motivated a growing scientific interest in understanding the factors and mechanisms promoting the CDOM increase. A proposed water color model for an important raw water source for Oslo, Norway, is based on the precipitation's amount and mobile ion concentration. The model explained more than 93% of the temporal variation in CDOM between 1983 and 2008. The model structure was also tested on three adjacent raw water sources and was found to explain 75-82% of the CDOM development throughout the same period. The long-term trend of increasing CDOM was closely related to the decline in sulfate and chloride concentrations in precipitation. Furthermore, interannual fluctuations in CDOM were explained by variation in predominant water flow paths, depending on amounts and intensity of precipitation, both of which are predicted to increase in several parts of the northern latitudes according to climate change scenarios.

Electrochemical impedance spectroscopic studies of the passive layer on the surface of copper as a function of potential

Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the oxide layer formed on a copper disc electrode and the changes that took place when treated potentiostatically in the range of -0.3 V to 0.9 V in buffer of pH 8.5. The response of an electrode using EIS, initially at equilibrium, to an applied potential was then modeled with equivalent circuits, proposed for different potential regions that completely illustrated the Cu/oxide/electrolyte systems and their properties in terms of 2 interfaces. Criterion for the applicability of equivalent circuit models was discussed. Changes in the film/metal interface as a function of potential were also probed at 30 mHz using Nyquist plots. Diffusion coefficient and concentration of mobile ions in the film calculated from the EIS data came out of the order of 10^{-6} cm^2 s^{-1} and 10^{-6} mmol mL^{-1}, respectively.

Structure, ionic conduction, and giant dielectric properties of mechanochemically synthesized BaSnF4

BaSnF 4 fluoride ion conductor has been prepared by mechanochemical milling technique at room temperature. The as-prepared material crystallizes in the cubic fluorite-type structure due to disordering of metal cations. The cubic phase transforms to tetragonal structure by annealing at 460 K. The ionic conductivity of the cubic phase is two to three orders of magnitude lower than the annealed sample. The complex conductivity of the investigated materials has been analyzed by a power-law model in order to extract the hopping rates and the concentration of mobile ions, the parameters that control the overall conduction behavior. The estimated values of the concentration of mobile ions are found to be of the same order, indicating that the conduction process is controlled by the mobility of charge carriers. BaSnF4 has been found to belong to a new class of nonoxidic giant dielectric constant materials with a value of ε′∼105, which is independent of temperature and frequency over wide ranges. It is found that the giant values of the dielectric constant are not due to surface barrier layer capacitance effects at the sample/electrode interface of the material.

Ion transport property studies on PEO–PVP blended solid polymer electrolyte membranes

The ion transport property studies on Ag+ ion conducting PEO–PVP blended solid polymer electrolyte (SPE) membranes, (1 − x)[90PEO : 10AgNO3] : xPVP, where x = 0, 1, 2, 3, 5, 7, 10 (wt%), are reported. SPE films were caste using a novel hot-press technique instead of the traditional solution cast method. The conventional solid polymeric electrolyte (SPE) film, (90PEO : 10AgNO3), also prepared by the hot-press method and identified as the highest conducting composition at room temperature on the basis of PEO–AgNO3-salt concentration dependent conductivity studies, was used as the first-phase polymer electrolyte host into which PVP were dispersed as second-phase dispersoid. A two-fold conductivity enhancement from that of the PEO host could be achieved at room temperature for PVP blended SPE film composition: 98(90PEO : 10AgNO3) : 2PVP. This has been referred to as optimum conducting composition (OCC). The formation of SPE membranes and material characterizations were done with the help of the XRD and DSC techniques. The ion transport mechanism in this SPE OCC has been characterized with the help of basic ionic parameters, namely ionic conductivity (σ), ionic mobility (μ), mobile ion concentration (n) and ionic transference number (tion). Solid-state polymeric batteries were fabricated using OCC as electrolyte and the cell-potential discharge characteristics were studied under different load conditions.

Ion Gel-Gated Polymer Thin-Film Transistors: Operating Mechanism and Characterization of Gate Dielectric Capacitance, Switching Speed, and Stability

We report comprehensive characterization of electrolyte-gated polymer thin-film transistors (TFTs) incorporating solution processable polymer semiconductors and high capacitance “ion gel” gate dielectrics. The ion gel dielectrics comprise self-assembled networks of triblock copolymers such as poly(styrene-b-methylmethacrylate-b-styrene) [PS-PMMA-PS] that are swollen with ionic liquids, e.g., (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). The capacitance of the gels is exceptionally large (>10 μF/cm2 at 10 Hz), which is derived from the high concentration of mobile ions and facilitates operation of ion gel-gated organic TFTs (GEL-OTFTs) at very low voltages (< 2.5 V). Gate-induced hole densities in GEL-OTFTs employing different polythiophene semiconductors in the channel are on the order of 1014 carriers/cm2, with associated saturation hole mobilities that are also remarkably large, ∼1 cm2/(V s), likely because of the large gate-induced carrier densities. Examination of the ...

Electrical relaxation in CdI2 doped silver vanadate superionic glasses

In this paper we have studied electrical relaxation in several compositions of CdI2–Ag2O–V2O5 superionic glasses in wide frequency and temperature ranges. We have used the power law formalism as well as the electric modulus formalism to analyze the experimental results. We have observed that the dc conductivity increases and the activation energy decreases with the increase of the CdI2 content in the compositions. We have also observed that the concentration of mobile Ag+ ions is not thermally activated and is almost independent of CdI2 content. The mobile ion concentration is also less than that of the total Ag+ ions present in the compositions. The conductivity is primarily determined by the mobility rather than the ion concentration. The conductivity relaxation time shows Arrhenius behavior with an activation energy, which is almost equal to that of the dc conductivity, indicating that the same ions take part in the dc and the ac conduction. The values of frequency exponent and stretching exponent are observed to be almost temperature and composition independent. The exponents are less than unity and obey the relationship proposed by Ngai.

The induced χ(2) in thermally poled lanthanum phosphate glass

We have studied thermal poling in lanthanum phosphate glasses with molar composition 0.2La 2O 30.8P 2O 5. A χ (2) can be induced for poling voltages above 3 kV and temperatures above 300 °C. The induced χ (2) profile consists of a single layer with a width of 30 μm near the anodic surface. The magnitude of the induced χ (2) is 0.88 pm/V. The results, which are similar to those of poled fused silica and very different from those found in high-alkali phosphate glasses, can be understood in terms of the very low (<1 ppm) concentration of mobile ions in this glass.

Molecular mobility and Li+ conduction in polyester copolymer ionomers based on poly(ethylene oxide)

We investigate the segmental and local dynamics as well as the transport of Li(+) cations in a series of model poly(ethylene oxide)-based single-ion conductors with varying ion content, using dielectric relaxation spectroscopy. We observe a slowing down of segmental dynamics and an increase in glass transition temperature above a critical ion content, as well as the appearance of an additional relaxation process associated with rotation of ion pairs. Conductivity is strongly coupled to segmental relaxation. For a fixed segmental relaxation frequency, molar conductivity increases with increasing ion content. A physical model of electrode polarization is used to separate ionic conductivity into the contributions of mobile ion concentration and ion mobility, and a model for the conduction mechanism involving transient triple ions is proposed to rationalize the behavior of these quantities as a function of ion content and the measured dielectric constant.