Electrical Double Layer Parameters Research Articles

Fitting the determined impedance in the guinea pig inner ear to Randles circuit using square error minimization in the range of 100 Hz to 50 kHz

Objective. Several lumped and distributed parameter models of the inner ear have been proposed to improve vestibular implant stimulation. The models should account for all significant physical phenomena that influence the current propagation, such as the electrical double layer (EDL) and medium polarization. The electrical properties of the medium are reflected in the electrical impedance; therefore, the study aimed to measure the impedance in the guinea pig inner ear and construct its equivalent circuit. Approach. The electrical impedance was measured from 100 Hz to 50 kHz between a pair of platinum electrodes immersed in 0.9% NaCl saline solution using sinusoidal voltage signals. The Randles circuit was fitted to the measured impedance in the saline solution in order to estimate the EDL parameters () of the electrode interface in saline. Then, the electrical impedance was measured between all combinations of the electrodes located in the semicircular canal ampullae and the vestibular nerve in the guinea pig in vitro. The extended Randles circuit considering the medium polarization () together with EDL parameters () obtained from the saline solution was fitted to the measured impedance of the guinea pig inner ear. The Warburg element was assumed negligible and was not considered in the guinea pig model. Main results. For the set-up used, the obtained EDL parameters were: The average values of intra-, extracellular resistances, and membrane capacitance were respectively. Significance. The obtained values of the model parameters can serve as a good estimation of the EDL for modelling work. The EDL, together with medium polarization, plays a significant role in the electrical impedance of the guinea pig inner ear, therefore, they should be considered in electrical conductivity models to increase the credibility of the simulations.

Amine-functionalized silica particles with magnetic core as magnetically removable adsorbents of Ag(I) ions

Adsorption of silver ions over amine-functionalized silica particles with magnetic core has been studied. This adsorbent has been synthesized via sol–gel method, in the presence of Fe3O4 particles as magnetic cores. As a comparison, magnetic silica adsorbent with non-functionalized surface was also synthesized. As-obtained materials have been characterized by elemental analysis, acid–base titration, nitrogen sorption measurements, X-ray photoelectron spectroscopy and scanning electron microscopy. What is more, parameters of electrical double layer at the silica adsorbent/electrolyte solution interface were also examined. Kinetic of adsorption and isotherms of silver ions were determined. The obtained adsorption of Ag(I) ions for the studied materials was in the range of about 0.2–0.3 mmol/g.

Assessment of ζ-potential in TiO2 aqueous suspensions: A comparative study based on thermodynamic and rheological methods

It is widely demonstrated that the distinct electrokinetic techniques lead to different values of ζ-potential despite what should be expected from the classical theory. Electrophoresis and conductivity measurements were used to estimate the ζ-potential and the electrical double layer parameters of TiO2 aqueous suspensions. An assessment of the results was made following thermodynamic and rheological methods. In the first case, the Gibbs free energy increment was compared. In the second one, the yield stress/ζ-potential plots were used. In spite of the ζ-potentials obtained from conductivity, electrophoresis and electrophoresis-conductivity combined techniques are different, the Gibbs free energy increment values do not discriminate the best ζ-potential value. Moreover, the correlation between the yield stress and the square of the ζ-potential has shown that all the ζ-potentials can physically be acceptable. Therefore, the only reasonably conclusion from this study is that the use of combined techniques, like electrophoresis-conductivity, should always be taken as the more cautious approach of evaluating ζ-potentials.

Adsorption of citrate ions on hydroxyapatite synthetized by various methods.

The specific adsorption of citric acid ions at hydroxyapatite interface was investigated by the means of radioisotope method (14C) as a function of citric acid ions concentration, NaCl concentration and pH. Application of the hydroxyapatite has become wide in the biomaterial field as the Ca10(OH)2(PO4)6 possess biocompatibility with human hard tissue. Hydroxyapatite was synthesized using three different methods. The physical properties of the resulting powder were characterized by DTA/TG, XRD, AFM and SEM microscopy. Physicochemical qualities characterizing the electrical double layer of the hydroxyapatite/NaCl solution interface were determined. The zeta potential and the adsorption of citric acid molecule were studied as a function of pH. The point of zero charge and the isoelectric point of samples were determined. Electrical double layer parameters of hydroxyapatite/NaCl interface are influenced by a synthesis method. The points pHpzc and pHIEP for sample 1 are pHpzc 7.5 and pHIEP 3; for sample 2 pHpzc 7.05 and pHIEP 3, for smaple 3 pHpzc 6.7 and pHIEP 3. Temperature has weak influence both on pure substance and with citric acid adsorbed, as derivatographic analysis has shown, and characterization of hydroxyapatite structure may be carried out by this thermal analysis. Two phenomena are responsible for citric acid adsorption: phosphate group’s replacement at hydroxyapatite surface by citric ions parallel to intraspherical complexes formation.

Electrical double layer characteristics of nanoporous carbon derived from titanium carbide

Electrochemical parameters of the nanoporous carbide-derived carbon|organic electrolyte have been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The gas adsorption measurements have been used for evaluating the specific surface area, pore size distribution and porosity as the essential parameters influencing the double layer performance of carbon. The region of ideal polarizability, values of series and parallel resistance, capacitance and other important electrical double layer parameters were established. It was shown that specific capacitance of typical nanoporous carbon derived from titanium carbide is in the range of 70–90 F cm −3 or 100–130 F g −1 and it depends on the synthesis conditions. The influence of the electrolyte solvent to the capacitance was insignificant, although acetonitrile was advantageous with respect of smaller viscosity.

Electrosurface Characteristics of (Hydr)oxides and Oxide Nanostructures in 1 : 1 Electrolyte Solutions. 3. Calculation of the Electrical Double Layer Parameters for Boehmite, Goethite, and Silicon Oxide According to Adsorption and Electrokinetic Data

The charge components, potentials, and capacities of the electrical double layer are calculated for aluminum, iron, and silicon (hydr)oxides on the basis of adsorption and electrokinetic measurements conducted in NaCl and KCl solutions. The dissociation degrees of surface groups in the point of zero charge and in the isoelectric point are estimated on the basis of the surface reaction constants. The 2-pK model in combination with the Graham model is shown to be applicable for describing the experimental results obtained for the systems in question.

The Electrical Double Layer Parameters for the Group 4 Metal Oxide/Electrolyte System

The electrical double layer parameters for Group 4 metal oxide/NaCl solution systems are presented. The surface charge density and the adsorption of background electrolyte ions as a function of the pH of the solution and the concentration of the electrolyte for the ZrO2 and HfO2 systems are presented. Through the use of numerical optimization, the apparent reaction constants for the surface hydroxy group were calculated. The characteristic points of the electrical double layer and the ionization and complexation constants of the surface hydroxy groups are compared with those predicted semi-theoretically.

Complex electrosurface investigations of dispersed microphases

The structure of the electrical double layer (EDL) of colloidal systems is discussed. The methods of determination of the most important parameters of the EDL, i.e. the value of the surface-potential ψ 0, the Stern-potential ψ δ and the electrokinetic-potential ζ, the surface charge density σ 0, the electrokinetic charge σ ζ, as well as the specific surface conductance κ σ and Rel parameter are described. The application of the theory of non-linear electrosurface phenomena developed by Dukhin, Derjaguin and Shilov for calculation of the EDL parameters is discussed. The above data of the EDL characteristics for polystyrene and melamin-formaldehyde latices, suspensions of AgI, Sb 2S 3, Fe 2O 3, ZrO 2, hydromica, palygorskyte, yeast cells as well as kerosene-in-water, ET grade lubricating oil technical emulsions in different electrolyte solutions are discussed. It has been shown that in the most of cases (with the exception of AgI solution) ψ 0 or ψ δ>ζ and σ 0≫σ ζ. It indicates the presence of a considerable free charge between the surface and slipping plane due to the formation of hydrodynamically immobile water layers on the surface in which the ions retain high mobility. The necessity of complex (integrated) electrosurface measurements for the description of the electrical double layer structure is stressed. A new kind of non-linear electrokinetic phenomena, namely the superfast electrophoresis is described. The phenomenon was predicted theoretically by Dukhin and Mishchuk and investigated experimentally in detail in the author's laboratory. It has been shown that the electrophoretic mobility of large (hundreds μm) ion-type conducting particles like ion-exchanger grains/fibres or electron-type conducting particles like Al/Mg alloy, graphite and activated carbon in strong electric fields (100–1000 V/cm) exceeds the electrophoretic mobility values typical for non-conducting particles by 1–2 orders of magnitude. The mobility of such particles depends on the conductivity ratio between the particles and medium and strongly increases with the electric field gradient and the particle size. This is in contrast to classical electrophoresis. The superfast electrophoresis is due to the interaction of a strong electric field with the space charge near the surface of unipolar conducting particles. This space charge is induced by the strong external field because of the concentration polarisation.

The Structure of the Electrical Double Layer at the LiChrospher-Type Adsorbent/Aqueous Electrolyte Solution Interface

The surface charge, adsorption densities of Na+ and Cl− ions and zeta potential at the LiChrospher/NaCl solution interface have been determined as a function of the pH of the solution and the NaCl concentration. The surface ionization and complexation constants have been calculated from potentiometric titration data. Some corrections in the calculation of electrical double layer parameters were made to account for impurities. An attempt to fit the surface complexation model to the surface charge and adsorption of background electrolyte ions at the LiChrospher/NaCl solution interface was made using numerical procedures. The additional adsorption of ions and the interaction of ions in the electrical double layer were considered in an attempt to improve the fit of the standard site binding model to the experimental data.

The adsorption of dimethyl sulfoxide on mercury electrodes

The adsorption of dimethyl sulfoxide (DMSO) at the mercury/DMSO + 0.15 M Na2SO4 interface is studied using the electrode charge density as the independent electrical variable and taking into account medium effects. In order to perform this analysis the mean activity coefficients of the salt in the presence of DMSO were experimentally determined and the electrical double layer parameters calculated by using Fawcett's function. The results suggest that upon adsorption the DMSO molecule, in the concentration range used, may suffer a partial reorientation process. The system can be described by Frumkin's isotherm but it is necessary to consider a variation of the maximum surface excess with the electrode charge.

Theoretical treatment of cholesterol monohydrate dissolution in Renex-690/ionic surfactant systems based on a physical model approach

The dissolution kinetics of cholesterol monohydrate in the presence of Renex-690 and ionic surface active agents (benzalkonium chloride and sodium dodecyl sulfate) are dramatically influenced by the addition of NaCl. The mass transfer resistances decreased with increasing electrolyte concentrations and attained an asymptotic value predicted for the aqueous boundary layer-controlled situation. Electrophoretic mobility studies showed that the mixed surfactants are adsorbed on the originally negatively charged cholesterol surface to an extent that the effective surface charge is attributed to the adsorbed surface active molecules. The results suggest that electrical repulsion between charged micelles and the cholesterol surface plays a dominant role in the mechanistic interpretation of the interfacial barrier to dissolution. A model embodying the classical Smoluchowski flocculation theory of colloidal particles and the DLVO potential energy theory of electrical double layer repulsion and dispersion attraction was applied to the dissolution data to obtain a quantitative description of the interfacial barrier in terms of surface charge densities, electrical double layer parameters, surface potentials, and dispersion force constants.

On the surface complexation model of the oxide-aqueous solution interface

The recent chemical models that describe oxide-aqueous solution reactions in terms of surface complexes are examined. It is shown that chemical thermodynamics can give a self-contained description of these reactions without hypotheses concerning the molecular structure of the interfacial region. Surface complexation models that combine concepts of coordination chemistry with those in electrical double-layer theory are attempts at molecular theory to account for the observed thermodynamic behavior of surface species. These models can be interpreted as applications of a statistical mechanical van der Waals model, according to which charged surface species interact mutually through a mean electric field created by themselves. The van der Waals model shows that the electrical double-layer parameters which appear in expressions for conditional equilibrium constants in surface complexation models represent contributions of the mean electric field to the rational activity coefficients of surface species.

Correlation between specific adsorption and corrosion inhibition. Adsorption of 1-butylpyridinium bromide

A correlation between specific adsorption and corrosion inhibition was made on the basis of calculations of the degree of coverage at zero charge on the electrode and corrosion rates. 1-butylpyridinium bromide (BPB) was choosen as a model compound for these studies. The electrical double-layer parameters were determined at constant charge on a mercury electrode, from values of the interfacial capacity and surface tension obtained experimentally from aqueous solutions of BPB at 25° C. The characteristics of the salt as a corrosion inhibitor were studied through Tafel plots and weight-loss measurements using mild steel plates immersed in H2SO4 solutions. Analysis of the results lead to the conclusion that the salt adsorbs intensely on the metal surface, forming a complete monolayer of BP+ ions in 0.1 mol dm−3 solutions and multilayers for higher concentrations. The results of this work indicate that for high coverages there is a good correlation between the amount of BP+ specifically adsorbed on mercury and the inhibition of the corrosion process on mild steel. That type of compound acts mainly as an anodic inhibitor in acid media by the formation of protective layers on the metal surface.

Electron transfer reactions in metal ammine complexes—IV: Reduction of some amino acid, aminobenzoic acid and their Schiff base substituted pentaammine Cr(III) complexes at the dropping mercury electrode

Aminoacid, aminobenzoic acid and their Schiff base substituted pentaammine Cr(III) perchlorate complexes undergo an irreversible, one electron reduction process at the dropping mercury electrode. The rates of the electrode process k app, calculated from the values of diffusion current at the end of the life of the mercury drop, show small enhancements in presence of iodide ions. On comparing these rate enhancement values with the corresponding value for the reduction of [Cr(NH 3) 6] 3+, which undergoes a completely outer-sphere path, it is concluded that these complexes follow a mixed inner/outer-sphere path. The contribution of the inner-sphere path is maximum in the case of aminoacid complexes and minimum in the case of Schiff bases of aminobenzoic acids. These results are further supported by the values of α app, obtained from Tafel plots and other electrical double layer parameters like ( δΦ r / δE) μ , ( δδ r / δq m ) μ and α corr.