Gouy Chapman Stern Grahame Research Articles

Structure of interfaces on mechanically renewed Sn, Pb, and Sn-Pb electrodes in acetonitrile solutions of surface inactive electrolytes

• Ideal polarizability regions of Sn and Pb electrodes in AN solutions were found. • Zero charge potentials of Sn and Pb in AN solutions were determined. • Time changes of capacitance curves are observed on Sn-Pb electrode after renewal. • It is shown that Pb atoms are squeezed out to the surface layer of Sn-Pb electrode. • Time effects on renewable Sn-Pb/AN solutions interface were analyzed in detail. The electrical double layer (EDL) structure of mechanically renewed electrodes of Sn, Pb, and Sn-Pb alloy (1 at.% Pb) is studied in acetonictrile (AN) solutions of LiClO 4 by the impedance method and cyclic voltammetry. The potential regions are found in which these electrodes can be considered in good approximation as ideal polarizable. In these solutions, the potentials of zero charge ( E σ = 0 ) on Sn and Pb electrodes are found to be –0.37 ± 0.02 and –0.59 ± 0.02 V (vs. aqueous SCE), respectively. The experimental dependences of the capacitance on the potential are shown to be in good agreement with the classical EDL model of Gouy–Chapman–Stern–Grahame. Based on the results of capacitance measurements carried out on renewed Sn-Pb electrodes, it is found that as the time of exposure of the renewed alloy surface to electrolyte increases, the C vs. E curves indicate that the concentration of lead atoms in the surface layer of alloy also increases, i.e., Pb is the surface-active component of these alloys. By analyzing the observed time effects, the surface coverage of Sn-Pb electrode by lead atoms (θ) is calculated in different time ( t ) after the renewal. It is shown that the θ vs. t dependences well agree with the model proposed earlier that describes the process of surface segregation of atoms of the surface-active component of eutectic alloys by the mechanism of surface diffusion. The kinetics of process of surface segregation of lead atoms on the mechanically renewed Sn-Pb electrode is compared for AN and aqueous solutions. The increase in θ is found to proceed slower in AN solutions than in aqueous solutions of the similar composition. The main reason for the differences observed is proposed.

How Well Can You Tailor the Charge of Lipid Vesicles?

Knowledge and control of surface charge or potential is important for tailoring colloidal interactions. In this work, we compare widely used zeta potential (ζ) measurements of charged lipid vesicle surface potential to direct measurements using the surface force apparatus (SFA). Our measurements show good agreement between the two techniques. On varying the fraction of anionic lipids dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG) mixed with zwitterionic dimyristoylphosphatidylcholine (DMPC) from 0 to 100 mol % we observed a near-linear increase in membrane surface charge or potential up to 20-30 mol % charged lipids beyond which charge saturation occurred in physiological (high) salt conditions. Similarly, in low salt concentrations, a linear increase in charge/potential was found but only up to ∼5-10 mol % charged lipids beyond which the surface charge or potential leveled off. While a lower degree of ionization is expected due to the lower dielectric constant (ε ∼ 4) of the lipid acyl chain environment, increasing intramembrane electrostatic repulsion between neighboring charged lipid head groups at higher charge loading contributes to charge suppression. Measured potentials in physiological salt solutions were consistent with predictions using the Gouy-Chapman-Stern-Grahame (GCSG) model of the electrical double layer with Langmuir binding of counterions, but in low salt conditions, the model significantly overestimated the surface charge/potential. The much lower ionization in low salt (maximum ∼1-2% of total lipids ionized) instead was consistent with counterion condensation at the bilayer surface which limited the charge that could be obtained. The strong interplay between membrane composition, lipid headgroup ionization, electrolyte concentration, and solution pH complicates exact prediction and tuning of membrane surface charge for applications. However, the theoretical frameworks used here can provide guidelines to understand this interplay and establish a range of achievable potentials for a system and predict the response to triggers like pH and salt concentration changes.

Experimentation and modeling of surface chemistry of the silica-water interface for low salinity waterflooding at elevated temperatures

Models predicting wettability alteration of mineral-brine-oil interfaces during low-salinity-waterflooding (LSW) should account for the elevated temperatures typically found in oil reservoirs. For the first time, high temperature ζ-potential (zeta potential) data for silica are collected and used to interpret surface chemistries and interactions at reservoir-like conditions to predict temperature’s effect on wettability alteration. Mobility data for amorphous silica in varying NaCl(aq) concentrations at 25, 100, and 150 °C and neutral pH were obtained through microelectrophoresis experiments. Calculated ζ-potentials were fit with surface complexation model (SCM) parameters to predict electrical double layer (EDL) parameters based upon the Gouy-Chapman-Stern-Grahame (GCSG) model. ζ-potentials increased with increasing temperature (around 50% increase from 25 to 150 °C) and decreasing NaCl concentrations (10−1–10−4 mol kg−1). These trends, along with Derjaguin-Verwey-Landau-Overbeek (DLVO) theory, suggests that overall repulsive forces extend farther from the surface at low salinity and higher temperatures, implying greater wetting thickness/surface wettability in these environments. The resulting surface concentration calculations suggest that LSW is most impactful up to 10−2 mol kg−1 of salt, and that additional dilution below 10−3 mol kg−1 will negligibly impact oil recovery, particularly at reservoir temperatures above 100 °C. The analysis provides a framework for treating more complex reservoir systems, such as carbonates in multivalent brines.

The difference between interfaces formed by mechanically renewed gold and silver electrodes with acetonitrile and aqueous solutions

The impedance method and cycling voltammetry were used in studying the structure of interface between mechanically renewable electrodes of Au and Ag and solutions with different concentration of LiClO4 in acetonitrile (AN). The obtained data allowed us to conclude that the considered systems are characterized by the wide potential regions in which these electrodes can be considered as ideally polarizable. These regions are: from −0.5 to 1.0V for Au and from −1.7 to −0.2V (vs. aqueous SCE) for Ag electrodes; the zero charge potentials of Au and Ag electrodes in these systems are: 0.62 and −0.37V, respectively. It was shown that, in the above-noted potential regions, the experimental C vs. E curves can be well described by the classical model of Gouy–Chapman–Stern–Grahame. It was shown, as well, that the difference in experimental zero charge potentials of Au and Ag electrodes correlates with the difference in electron work functions of these metals. These data allow us to conclude that the interaction at the interface between renewable Au and Ag electrodes and AN solutions can be characterized as lyophobic, i.e., close to that observed for Hg/AN and mercury-like metals/AN systems. On the other hand, the interfaces of Au and Ag electrodes with aqueous solutions should be considered as hydrophilic systems being radically different from the interfaces of Hg and mercury-like metals with aqueous solutions. It was demonstrated that the specific features of the interface structure on Au and Ag electrodes in contact with aqueous and AN solutions can be well described on the qualitative level within the framework of phenomenological model of «two limiting states».

A discussion on ion conductivity at cation exchange membrane/solution interface

Abstract By Gouy–Chapman–Stern–Grahame (CGSG) model, the electric double layer at ion exchange membrane/solution interface consists of two parts: the Stern layer and the diffusion layer. The ions in Stern layer are compacted and considered to be immobile. The relation of diffusion layer mean conductivity K with outer Stern layer potential φ 0 , the boundary potential φ δ and the electrolyte concentration C 0 is educed for symmetric electrolyte system. The results show that K is higher than that of the bulk solution and is greatly influenced by φ 0 , φ δ and C 0 . The examination of PE01 cation exchange membrane/solution interface resistance R e measured by ac impedance technique, shows that R e value decreases quickly as the KCl electrolyte concentration rises. The effect of electrolyte concentration on the resistance of EDL can be explained by the electrical interactions between ions and charged groups of the membrane. Since the membrane/solution interface resistance is much higher than that of bulk solution, therefore, a further analysis based on the theory developed in this study proves that the ion transfer resistance R e of membrane–solution interface predominantly occurs at Stern layer as a result of static electrical interaction.

Electrical double layer interactions between dissimilar oxide surfaces with charge regulation and Stern–Grahame layers

Models of surfaces with intrinsic ionisable amphoteric surface sites governed by the dissociation of acid–base potential determining ion species together with the capacity for the adsorption of anion and cations of the supporting electrolyte are required to describe both the results of electrokinetic and titration measurements of inorganic oxides. The Gouy–Chapman–Stern–Grahame (CGSG) model is one such model that has been widely used in the literature. The electrical double layer interaction between two dissimilar CGSG surfaces has been studied by Usui recently [S. Usui, J. Colloid Interface Sci. 280 (2004) 113] where erroneous discontinuities in the slope of the pressure–separation relation were observed. We revisit this calculation and provide a simple general methodology to analyse the electrical double layer interaction between dissimilar ionisable surfaces with ion adsorption.

Interaction between dissimilar double layers with like signs under charge regulation on the basis of the Gouy–Chapman–Stern–Grahame model

The force of interaction between two flat double layers with dissimilar surface potentials but of the same signs, in contact with 1-1 electrolyte solutions (0.001, 0.01, and 0.1 M), was calculated as a function of the surface separation. The calculation was carried out on the basis of the Gouy-Chapman-Stern-Grahame double-layer model, incorporating the site-dissociation and site-binding model used previously for many oxide studies. The results demonstrated that the interaction force under surface charge regulation was always repulsive, increasing progressively with decreasing surface separation. This result is in contrast to the predictions of previous theories that are based on the Gouy-Chapman (GC) double-layer model. Dependence of surface potentials and surface charge densities on the surface separation is also presented.

Specific Features of the Structure of the Electrical Double Layer on Intermetallic Compound Ag3Sn in Aqueous Surface-Inactive Electrolytes

The behavior of a polycrystalline electrode of intermetallic compound Ag3Sn in aqueous NaF solutions is studied using an impedance method. At potentials of –1.3 to –0.6 V (SCE), the electrode may be viewed as ideally polarizable. The Gouy–Chapman–Stern–Grahame model quite satisfactorily describes capacitance curves obtained at various electrolyte concentrations. Experimental capacitance curves for an Ag3Sn electrode are compared with those for polycrystalline Ag and Sn electrodes renewed by cutting. Characteristics of an Ag3Sn electrode are unique and its capacitance curves cannot be simulated from the data for Ag and Sn electrodes within the known phenomenological approaches.

Acidity and Alkali Metal Adsorption on the SiO 2–Aqueous Solution Interface

The intrinsic deprotonation constant (p K int a 2 ) and the intrinsic ion exchange constants (p K int Me + ) of Li +, Na +, and K + on SiO 2 were uniquely determined at 30°C by using the potentiometric titration data, the Gouy–Chapman–Stern–Grahame (GSCG) model for the structure of the electrical double-layer (edl) and the double-extrapolation method. The values of these constants were p K int a 2 =6.57, p K int Li + =p K int Na + =p K int K + =5.61. The chemical meaning of intrinsic equilibrium constants and the equality in the values of p K int Li + , p K int Na + and p K int K + were discussed.

Zeta Potential of Stearic Acid Monolayer at the Air–Aqueous Solution Interface

The zeta (ζ) potential of an insoluble monolayer of stearic acid at the air–water interface was measured as a function of pH in the presence of 0.0001, 0.001, and 0.01 M NH4NO3. The ζ potential was measured by means of the plane interface technique which involved the determination of the electrophoretic velocity profile of reference (polystyrene latex) particles along the solution depth in a rectangular open quartz cell. The ζ vs pH relationship at 0.001 and 0.01 M NH4NO3 was analyzed in terms of the Gouy–Chapman–Stern–Grahame model for electrical double-layer incorporating a simple site-binding model used previously for many oxide and latex colloid studies. The dissociation constant (pKa) of stearic acid monolayer and double-layer parameters such as integral capacitances of inner and outer Helmholtz layers and the complexation constant of counterion complexes were also estimated.

Zeta Potential of Insoluble Monolayer of Long-Chain Alcohol at the Air–Aqueous Solution Interface

The zeta potential of a close-packed insoluble monolayer of 1-hexacosanol at the air–water interface in the presence of 0.001 M NH4NO3 was measured as a function of pH by means of the plane interface technique. The negative zeta potential increased with the increase of pH up to about 9. The negative charge at the monolayer–water interface is considered to be due to the dissociation of protons from hydrated alcohol water clusters at the surface. The zeta potential results were analyzed in terms of the site dissociation and site-binding mechanism within the Gouy–Chapman–Stern–Grahame double-layer model of the metal oxide–water interface.

Electroreduction of peroxodisulfate anion at Bi(111) single-crystal plane electrode

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O 8 2- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O 8 2- . The charge number of the reacting S2O 8 2- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O 8 2- concentration in solution if cNaF = const. However, CTP noticeably depend onc NaF.

Electroreduction of peroxodisulfate anion at a Cd(0001) single-crystal plane electrode

Electroreduction of peroxodisulfate anion on electrochemically polished face Bi(111) in aqueous NaF solution with different additions of Na2S2O8 is studied by rotating-disc voltammetry. The S2O82- electroreduction rate depends on the electrode potential and base-electrolyte concentration, i.e. on the diffuse layer thickness. The kinetic current densities atE = const are obtained by the Koutecky-Levich method and used for the determination of the apparent rate constants of electroreduction of S2O82-. The charge number of the reacting S2O82- species is obtained; it depends on the surface-inactive electrolyte concentration and the electrode potential. The ψ0 potential values at the outer Helmholtz plane, obtained for various NaF + H2O systems according to Gouy-Chapman-Stern-Grahame (GCSG) model, are used for constructing corrected Tafel plots (CTP), which are linear atE- ψ0 < -0.9 V (SCE). The charge transfer coefficient oc for electrochemically polished Bi(111) somewhat decreases with the concentration of the base electrolyte (0.22 ≤α ≤0.27), but the value of α is practically independent of the S2O82- concentration in solution if cNaF = const. However, CTP noticeably depend oncNaF.

Zeta potential measurements with fibre plugs in 1:1 electrolyte solutions

The aim of this paper is correct calculation of zeta potential values from streaming potential measurements in aqueous electrolyte solutions. To determine correct zeta potential values it is very important to measure the total electric conductivity exactly and to consider the electrode polarization. The streaming potential measurements of various fibre samples in KCl solution of different concentrations were carried out by means of two different measuring devices working in very different pressure ranges. The calculated zeta potential values show that the measuring method gives well reproducible results independent of the applied pressure and the kind of device. In addition, we discuss the possibility of, and the reason for, a maximum observed sometimes in the dependence of zeta potential values on the electrolyte concentration in the case of 1 : 1 electrolytes by means of measurements of a fibre diaphragm and by using computer simulations based on a Gouy—Chapman—Stern—Grahame model.

Mechanistic studies of electroosmotic control at the capillary-solution interface

The electrokinetic phenomena at the silica-solution interface under the influence of applied radial electric potential gradient were analyzed by a theory based on the Gouy-Chapman-Stern-Grahame (GCSG) model and the induced effect across the capillary wall. The effect of adsorbed ions at the silica-solution interface on the direct control of electroosmosis was studied with the application of lithium ions, tin(IV) ions, and dodecyltrimethylammonium bromide (DTAB). In addition, various organic coatings, including butyl phase, amino phase, and (glycidoxypropyl)trimethoxysilane-ethylene glycol diglycidyl ether (GOX-EGD), were employed for investigating the effect of surface deactivation on the direct control of electroosmosis

Electrokinetics of the silica-solution interface: a flat plate streaming potential study

Details for the construction of a flat plate streaming potential apparatus are presented. Measurements using this apparatus on fused silica slides are reported and analyzed on the basis of a Gouy-ChapmanStern-Grahame (GCSG) model for the electrical double layer at the silica-aqueous solution interface. It is found that the GCSG model can only partly account for the experimental results. Possible reasons for the discrepancy between experiment and theory are discussed.