Diffuse Layer Charge Research Articles

Thickness transitions in lysolecithin foam films

Microscopic foam films have been obtained from aqueous palmitoyl lysophosphatidylcholine (lyso PC) solutions and the effect of the monovalent Na − and divalent Ca 2− on their equilibrium thickness has been studied. At low NaCl concentrations, silver-coloured films have been obtained. A thickness transition zone is found with increase in NaCl concentration. leading to the formation of Newtonian black films (NBF). These results are compared with previous results obtained for microscopic films of non-ionic surfactant solutions. A remarkable effect of divalent Ca 2− on the properties of the films is found. In the interval 0.0001–0.0008 mol dm −3 CaCl 2, NBF are obtained. When the electrolyte concentration ( C cl) is increased to 0.001 mol dm −3 CaCl 2, a transition from NBF to silver films is observed. The thickness of these films decreases with further increase in C cl, until transitions to common black films, and subsequently again to NBF, are observed. This result is interpreted as due to specific interaction ofCa 2− ions with the intrinsically uncharged phospholipid head groups. In the case of lyso PC foam films with CaCl 2 added, direct measurements of the disjoining pressure vs thickness ( II ( h)) isotherms have been performed and a barrier-like transition to NBF is found. The results are discussed in connection with the predictions of the DLVO theory. In the case of NaCl, the diffuse electric layer potential (φ 0) and charge density (σ 0) are low, similar to the results obtained for non-ionic surfactant films. In the case of CaCl 2, an increase in C cl, leads to an increase in φ 0, and σ 0, which is interpreted as due to increased divalent ion binding. The comparison between the experimental II ( h) isotherms and the theoretical predictions shows that in the cases of low φ 0 and σ 0 studied, at constant C cl, electrostatic repulsion under the conditions of constant charge is operative. The results are considered in connection with the possibilities of using the microscopic foam film model for biological studies.

Components of the measured surface charge of low temperature ceramic oxides

This paper contains an analysis of the interfacial behaviour of samples of monoclinic zirconia. The oxide powder was obtained by calcining a hydrothermal precursor at 200° C. Results of surface charge determinations are elaborated to yield total capacitance values which, in turn, are analyzed on the basis of Parsons and Zobel (P-Z) plots (R. Parsons and F.G.R. Zobel, J. Electroanal. Chem., 9 (1965) 333). The aptitude of selecting either a planar or a spherical geometry for the diffuse double layer is discussed. Analysis of the results in P-Z coordinates indicates that samples subjected to the “routine” overnight conditioning in the solution present only effects due to simple diffuse double layer charge compensation. In the case, instead, of samples conditioned for a longer time (143 h), different components of the surface charge become apparent. Phenomena related to bulk penetration of the base electrolyte are suggested to occur in the latter case.

Electro—optic investigation of oxide suspensions. Mechanism of formation of the induced dipole moment

A model system (aqueous suspension of aluminium oxide particles) is used for the investigation of the mechaism of formation of the induced dipole moment, causing the large low-frequency electro—optic effects exhibited by colloid suspensions. The results demonstrate that the induced moment in the kilohertz frequency region is created only by the diffuse part of the surface electric double layer. The relaxation frequency of the induced moment shows a distinct dependence on the diffuse layer charge density. A surface conductivity mechanism is in accordance with the presented results.

Impedance spectroscopy of pure water in the 0.01 Hz to 100 kHz range

The complex impedance of a water-filled cell has been measured in the frequency range between 0.01 Hz and 100 kHz at temperatures ranging between 5°C and 80°C. The obtained results have been interpreted according to the Gouy, Chapmann and Stern model describing the water behaviour in the presence of electrode interfaces. The deconvolution of the measured complex impedance allowed to separate the contribution arising from the «bulk» water from those due to the Helmholtz layer and to the diffuse charge layer occurring at the electrode interface. The capacitance and resistance of the three layers are reported and their frequency and temperature dependences are briefly discussed. The use of this method as a tool to investigate the low-frequency dielectric properties of water is suggested.

The effect of temperature and ion type on the effective charge in polystyrene latices

The effect of temperature and co-ion and counterion type on the diffuse layer charge of monodisperse polystyrene latices was examined. A megahertz conductivity/dielectric technique, coupled with electrokinetic measurements, was used to obtain an estimate of the diffuse layer charge from the theory of the polarized double layer. Negatively charged latices with low surface charge (<7 μC cm −2) show no evidence of a Stern layer in simple indifferent electrolytes, but do so in the presence of cesium and alkylammonium ions. Highly charged cationic latices show strong counterion binding with all of the simple halide ions. The combination of electrokinetic and conductivity measurements would appear to provide a promising new technique for evaluating diffuse layer charge and potential.

Equilibrium distributions of electric field in a cell with adsorbed charge at the surfaces

Ionic charge that is stuck at the solid-liquid surface attracts a diffuse layer of ions of the opposite sign in the liquid. The asymmetry in the electric field distribution that results when an applied field is combined with the intrinsic field in the diffuse charge layer has been cited as a possible cause of the dc switching effect observed in liquid crystal displays based on bistable boundary layer configurations [Robert B. Meyer and R. N. Thurston, Appl. Phys. Lett. 43, 342 (1983)]. Since the ratio of Debye screening length LD to cell depth d is an important parameter, it is useful to solve for the static equilibrium field distribution under constant voltage in a finite cell where LD/d is not small. This problem is solved here.

Variation of the potential of the stern plane with interaction of dissimilar flat electrical double layers

The potential, Ψ δ , of the Stern planes of dissimilar double layers were calculated as a function of the separation distance. Also the surface charges, the Stern layer charges, and the diffuse layer charges were computed under the assumption of constant surface potentials. The dependence of Ψ δ on the parameter κ d (κ is the Debye reciprocal length parameter, d is half distance of separation) is distinct when κd < 1, particularly when the specific adsorption potential, φ, ∼0. As φ increases to ∼5 kT the dependence of Ψ δ on κ d is less distinct. It was found that the linear approximation is allowed for the system of high specific adsorption potential and high value of κ.

Surface and diffuse-layer charge at the TiO 2—electrolyte interface

We determine quantitatively the charge density in different parts of the double layer (Stem model) at the TiO 2—electrolyte interface using three complementary techniques (potentiometry, electrophoresis, radiotracer technique). The experimental determination of the adsorption of Na + and Cl − ions is shown to satisfy the Stern—Grahame isotherm, assuming that the double layer to represented by a series of capacitors where the outer one has a constant capacitance of about 22.8 μF cm −2.

Preparation of Surfactant-free Polystyrene Latices with High Surface Charge and Electrical Double Layer on Their Surfaces

Abstract Polystyrene latices with a wide range of surface charges were prepared in the absolute absence of conventional emulsifiers by controlling the concentration of potassium peroxodisulfate as an initiator and allowing the polymerization to proceed at a relatively high pH to suppress the Kolthoff reaction; KHCO3 or K2HPO4 buffer was used to keep the polymerizing system near neutral pH. Conductometric titrations with different bases (NaOH and Ba(OH)2) on latices show that the Stern layer charge increases with an increase in the surface charge of latices (σ0) and at about the same rate as σ0 does, leading to a virtually constant diffuse layer charge.

CHARGE DISTRIBUTION IN ELECTRIC DOUBLE LAYER ON POLYSTYRENE LATTICES

Abstract Conductometric titration curves using some bases give important knowledge about the structure of the electric double layer on the surface of polystyrene lattices. This analysis showed that the Stern layer charge increases with an increase in the surface charge of latex(δO) and at about the same rate as δO does, reaching a virtually constant diffuse-layer charge.

On the specific adsorption of anions from solutions of low ionic strength

The specific adsorption of anions at positive electrodes from solutions of low ionic strength is examined on the basis of the electrostatic (Stern-Levine) model for specific ionic adsorption. It is shown that as the ionic strength is decreased, the adsorbed charge density falls below the electronic charge density on the metal; for these conditions, high positive potentials are expected at the outer Helmholtz plane. The above model predicts that there is no extended potential region where the diffuse-layer charge is zero. Difficulties in estimating the potential drop across the diffuse layer in dilute solutions are discussed and a possible defect in the simple application of the Stern-Levine model pointed out.

On the specific adsorption of anions from solutions of low ionic strength

The specific adsorption of anions at positive electrodes from solutions of low ionic strength is examined on the basis of the electrostatic (Stern-Levine) model for specific ionic adsorption. It is shown that as the ionic strength is decreased, the adsorbed charge density falls below the electronic charge density on the metal; for these conditions, high positive potentials are expected at the outer Helmholtz plane. The above model predicts that there is no extended potential region where the diffuse-layer charge is zero. Difficulties in estimating the potential drop across the diffuse layer in dilute solutions are discussed and a possible defect in the simple application of the Stern-Levine model pointed out.

The prediction of electrokinetic phenomena within multiparticle systems: II. Sedimentation potential

A geometric cell model for a concentrated suspension in aqueous electrolyte of identical charged dielectric colloidal spheres was employed in an earlier paper in a theory of electrophoresis and electroosmosis. The same model is used here to study the related phenomenon of the sedimentation of such a suspension. The theory is restricted to small surface potentials (in the linear Debye-Huckel range) and to values of κ a ≳ 10, where a is the particle radius and 1/κ is the double layer thickness. The distortion from spherical symmetry in the diffuse layer charge density within a cell (the relaxation effect) due to the sedimentation is described by a simple approximation. A steady state “streaming potential” condition of zero net current flow through a cell and also Henry's condition of zero normal component of current flow at a particle surface are used to calculate the induced dipole moment, the induced sedimentation electric field and the sedimentation velocity. For very dilute suspensions and thin double layers, these calculated quantities tend towards the classic results of Smoluchowski, as required. In the limiting case of a single particle the value obtained for the sedimentation velocity lies between those calculated by Smoluchowski and by Booth. The predictions for the sedimentation velocity in concentrated suspensions are consistent with the rather limited experimental data available in the literature.

Computer simulation of the development process in electrophotography

A formulation for the toner deposition time constant <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> was derived and the effect of each of the variables appearing in it or the toner deposition equation was studied by computer simulation. The simulations were performed using toners containing 10 and 20 particle sizes over a range of size frequency distributions. It was found that the effect of each variable was quite dependent upon the values of the other variables. The variables were: depletion-rate constant <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> time <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> , capacitance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</tex> , electrode spacing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> , toner particle concentration <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> , particle diameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PD</tex> , charge per particle <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CP</tex> , and three choices of thickness of the diffuse double layer: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WC</tex> --very diffuse-coupled with the charge per particle varying with the diameter of the particle, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WB</tex> --normal-coupled with the charge per particle varying with the surface area of the particle, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WA</tex> -- tightly bound-coupled with the charge per particle varying with the volume of the particle. When the variables were such that the maximum in the distribution function for the deposited toner particles was at the lower end of the particle size range, increase in the depletion-rate constant shifted the maximum toward the upper end of the particle size range when the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">KT</tex> product became greater than 0.1 and decreased the rate of deposition. However, when the variables were such that the maximum in the distribution function for the deposited toner particles was at the upper end of the particle size range, increase in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> merely decreased the rate of deposition without affecting particle size distribution. In general, large values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> , small values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> , short time periods, large values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</tex> , and large values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> tended to push the distribution of the deposited toner toward the upper end of the particle size range. Large values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> , large values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> (restricted to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">KT &lt; 1</tex> ), and small values of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</tex> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> tended to push the distribution maximum toward the lower end of the particle size range. The variables <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</tex> , <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> , and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PD</tex> strongly affected the magnitude of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> while <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</tex> did not affect the magnitude of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> unless <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">KT</tex> >0.1. For a given particle size range, the ratio of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for the smallest particle to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for the largest particle was invariant with respect to the magnitude of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> . The range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for a given particle size range was much less for the very diffuse layer (charge was a linear function of the diameter) than for the normal layer (charge was a linear function of the surface area) and even less than for the tightly bound layer (charge was a linear function of the volume). Change in particle size range affected the ratio of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> for the smallest to largest particle in the range. Size frequency distributions with a maximum at some particle size or sizes tended to control the distribution of deposited particles at short deposition times ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t&lt;1 \micro s</tex> ), but could not control the distribution of deposited particles at long deposition times ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t &gt; 1</tex> ms). The choice of diffuse double layer and coupled charge dependency had very large effects on the magnitude of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> and the effect of some of the variables on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</tex> . The input-output tests showed that for a density range of 0 to 1.5, the response of the photoconductor in the present model was unsatisfactory and that a better simulation of latent image formation is required.

Diffuse layer charge relaxation at the ideally polarized electrode

Diffuse layer charge relaxation at the ideally polarized electrode

Diffuse layer charge relaxation at the ideally polarized electrode

When an ideally polarizable electrode pair is subjected to small pulses of charge, electrolyte ions are assumed to respond in conformance with the Nernst-Planck equation in its time-dependent form. For small potential perturbations, the time-dependent charge density equation has been solved to determine the time dependences of the spatial distribution of electric field, electrolyte charge density and ionic current. Integration of the electric field across one-dimensional and spherically symmetric cells leads directly to the linearized Gouy-Chapman level impedance of the ideally polarizable electrode and its diffuse ionic double layer. From the impedance, the real and imaginary parts, the series and parallel equivalent capacitances and resistances are computed as function of frequency. In particular, the series capacitance can be represented as a series-parallel network made up exclusively of frequency-independent parameters: geometrical capacitance, double-layer capacitance κε and the solution resistivity. The frequency dependence of the series capacitance arises in this model from the slow relaxation of the ionic atmosphere. This dispersion occurs at lower frequencies than were computed previously by Ferry. Rather than a dispersion depending on ω −1/2 , a Debye form dispersion depending on ω −2 is predicted. Short time current responses to voltage steps are also derived in addition to the more fundamental voltage response after charge injection. Continuity of the cation and anion transference number values from bulk to the outer Helmholtz plane are predicted for ions with the same or different mobilities.

Solid phase properties and colloid chemistry

Emphasis is placed on solid state properties, which may play an important role in colloid phenomena. The magnitudes of zeta potentials and double layer capacities are affected by the presence of a diffuse charge layer in the solid phase. Several possible models of double diffuse double layers are discussed. A calculation is given of the adsorption curves of Ag+ and I– on AgI, assuming diffuse charge layers in the solid as well as in the liquid phase. A good fit with the experimental data could be obtained with two parameters: the fraction of the number of lattice defects in AgI, 0.17 %, and a potential difference between the surface and the interior of the AgI-crystals, –53 mV, both at 20°C.

Forces between Lecithin Bimolecular Leaflets Are Due to a Disordered Surface Layer

The long-range repulsion observed between bileaflets of lecithin cannot be explained either with the usual view that the polar groups are arrayed coplanar with the bileaflet surface or by the assumption that charges protrude straight into the aqueous environment. Statistical-thermodynamic analysis of experimental data suggests rather that structure of the leaflet surface is better described as a diffuse charge layer. Forces between leaflets are caused largely by entropy changes in the surface with leaflet separation.

The application of the verwey and overbeek theory to the stability of kaolinite-water systems

A general method for measuring the adsorption of various anions on kaolinite has been presented. Using this method, the adsorption of citrate ions and hydroxyl ions on kaolinite has been described over the alkaline pH range. It has also been shown that the adsorption of these ions does not occur primarily on either the edges or faces of the kaolinite crystal, but probably occurs uniformly over the surface of the particle. The adsorption measurements permitted the calculation of all quantities pertinent to the Verwey and Overbeek theory. This, in turn, permitted a quantitative test of the applicability of this theory to the stability of kaolinite-water systems. It was found, with no overt contradictions, that a great deal of the viscous behavior of aqueous kaolinite suspensions could be explained on the basis of this theory. The results also permitted the formulation of a mechanism for the flocculation and deflocculation of aqueous kaolinite suspensions. It has been shown that three circumstances control the repulsion between particles. These are the extent to which the diffuse parts of the double layers of the particles interact, the total charge of the particles and the potential existing between the surface of the particles and the intermicellar solution, and the distribution of charges in the diffuse part of each double layer. It has also been shown that, in most cases, the effects of charge and potential are of minor importance and that the dispersion and flocculation of aqueous kaolinite suspensions depend only on the effects of diffuse layer interaction and charge distribution in the diffuse layer.

Initial oxidation rate of nickel and effect of the curie temperature

Nickel foil was oxidized for 24 hr periods within the temperature range 307° to 442°C producing NiO films up to 3400 Å thick maximum. A discontinuity in oxide growth is observed at the Curie temperature (353°C). Data obtained at 390°, 394° and 405°C as a function of time show that a two-stage oxide growth rate occurs, a higher rate following an initially lower rate. Both stages are represented by a linear relation between oxide thickness and logarithm of time. Many initial oxidation rate data obtained by other investigators, for Ni and a variety of metals, also follow the two-stage logarithmic equation. Based on control of the initial oxidation rate by electron transfer from metal to oxide, the discontinuity of oxide thickness at the Curie temperature is explained by an observed work function of nickel slightly higher above the Curie temperature than below. The change of work function also explains a slightly higher activation energy for oxidation above the Curie temperature than below. Calculations show that the density of trapped electrons in a constant density space charge next to the metal surface is 1.3 × 10 16 at 390°C. Density of available sites for trapped charge in a diffuse charge layer, which grows on top of the constant density layer, is the same order of magnitude (5.5 × 10 15). A higher density of sites for NiO than for Cu 2O, plus a higher work function for Ni than for Cu, are in line with a lower oxidation rate of Ni compared to Cu. It is calculated that contact of oxide with Ni or Cu lowers the work function at the metal-oxide interface by about 0.6 V. This value agrees, in the case of Cu 2O, with the energy required to excite an electron from the filled band to the conduction band.