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The electrocapillarity and zero-frequency differential capacitance, Cd, have been studied using pendant drop method, at the Hg interface of an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C2mim+][TFSA−], and have been compared with those of [C2mim+]BF 4 − , an IL with the common cation and a different anion, to focus on the anion dependence of zero-frequency Cd. The Hg interface of [C2mim+][TFSA−], the IL of the larger anion in the present study, exhibits greater zero-frequency Cd than that of [C2mim+]BF 4 − , the IL of the smaller anion. This behavior contradicts a simple expectation in which larger ion leads to smaller Cd. This apparent contradiction is explained by proximity of the charged moiety of TFSA− to the electrode surface compared with that of BF 4 − . The potential dependence of zero-frequency Cd for the two ILs both exhibits one-hump camel shape around the potential of zero charge (Epzc), which has been predicted to be specific behavior of the electrical double layer of ILs by theory and simulation. The humps are located at potentials more negative than Epzc. From a mean-field lattice-gas theory for the EDL in ILs, this negative shift can be interpreted that the charged moiety for C2mim+ is more easily condensed in the EDL than those for BF 4 − and TFSA−.

Micro- to nanosized droplets of liquid metals, such as eutectic gallium indium (EGaIn) and Galinstan, have been used for developing a variety of applications in flexible electronics, sensors, catalysts, and drug delivery systems. Currently used methods for producing micro- to nanosized droplets of such liquid metals possess one or several drawbacks, including the lack in ability to control the size of the produced droplets, mass produce droplets, produce smaller droplet sizes, and miniaturize the system. Here, a novel method is introduced using acoustic wave-induced forces for on-chip production of EGaIn liquid-metal microdroplets with controllable size. The size distribution of liquid metal microdroplets is tuned by controlling the interfacial tension of the metal using either electrochemistry or electrocapillarity in the acoustic field. The developed platform is then used for heavy metal ion detection utilizing the produced liquid metal microdroplets as the working electrode. It is also demonstrated that a significant enhancement of the sensing performance is achieved by introducing acoustic streaming during the electrochemical experiments. The demonstrated technique can be used for developing liquid-metal-based systems for a wide range of applications.

The structure of the polarised interface between two immiscible electrolyte solutions (ITIES) has usually been deduced from electrocapillarity and capacitance measurements. However, these two methods only offer an indirect access to the surface change density, by differentiation and integration. In this work, we analyse the dependence on the potential difference and the organic phase electrolyte concentration of the surface charge density of the polarised ITIES. Our study is based on electrocapillarity, capacitance and surface second harmonic generation (SHG). This spectroscopic approach allows us to probe directly ionic concentrations and hence surface charge density. By comparing the results provided by these different methods, we confirm that integration of the capacitance curves yields too large values of the charge density. On the other hand, electrocapillarity and SHG provide consistent results over a large potential range. These results depict an ITIES weakly affected by the organic electrolyte concentration. Furthermore, the surface charge density depends quasi-linearly on the potential difference, at all concentrations. Altogether, these results support the model of a polarised ITIES made of two ionic face-to-face layers and devoid of diffuse layer, the so-called discrete Helmholtz model.

The structure of ionic liquids (ILs) at the electrochemical IL|Hg interface has been studied using the pendant drop method. From the electrocapillarity (potential dependence of interfacial tension) differential capacitance (Cd) at zero frequency (in other words, static differential capacitance or differential capacitance in equilibrium) has been evaluated. The potential dependence of zero-frequency Cd at the IL|Hg interface exhibits one or two local maxima near the potential of zero charge (Epzc), depending on the cation of the ILs. For 1-ethyl-3-methylimidazolium tetrafluoroborate, an IL with the cation having a short alkyl chain, the Cdvs. potential curve has one local maximum whereas another IL, 1-octyl-3-methylimidazolium tetrafluoroborate, with the cation having a long alkyl chain, shows two maxima. These behaviors of zero-frequency Cd agree with prediction by recent theoretical and simulation studies for the electrical double layer in ILs. At negative and positive potentials far from Epzc, the zero-frequency Cd increases for both the ILs studied. The increase in zero-frequency Cd is attributable to the densification of ionic layers in the electrical double layer.

The adhesion between colloidal silica particles and modified electrodes has been studied by direct force measurements with the colloidal probe technique based on the atomic force microscope (AFM). The combination of potentiostatic control of gold electrodes and chemical modification of their surface with self-assembled monolayers (SAMs) allows for the decoupling of forces due to the electrical double layers and functional groups at the solid/liquid interface. Adhesion on such electrodes can be tuned over a large range using the externally applied potential and the aqueous solution's ionic strength. By utilizing cantilevers with a high force constant, it is possible to separate the various contributions to adhesion in an unambiguous manner. These contributions comprise diffuse-layer overlap, van der Waals forces, solvent exclusion, and electrocapillarity. A quantitative description of the observed adhesion forces is obtained by taking into account the surface roughness of the silica particle. The main component of the adhesion forces originates from the overlap of the electrical double layers, which is tuned by the external potential. By contrast, effects due to electrocapillarity are of only minor importance. Based on our quantitative analysis, a new approach is proposed that allows tuning of the adhesion force as a function of the externally applied potential. We expect this approach to have important applications for the design of microelectromechanical systems (MEMS), the development of electrochemical sensors, and the application of micro- and nanomanipulation.

Electrocapillarity is the basis of modern electrowetting. And room temperature ionic liquids, an increasingly important set of electrolytes and organic salts that are liquid at room temperature, are considered a novel class of electrowetting agents, because of non-significant vapor pressure, nonflammability, good thermal stability, and a wide useable temperature range. In this paper, a simple device has been fabricated to investigate the electrocapillarity of ionic liquids. It shows attractive features involving wide operating temperature and in particular high stability, fast response and good reversibility at high temperatures. Besides, electrocapillarity of ionic liquids is strongly dependent on power supply frequency. In particular, high frequency, stable, reversible and wide height of rise modulations were obtained. The phenomenon of ionic liquids-based electrocapillarity was found to be affected by the structure and physicochemical properties of ionic liquids such as density, surface tensio...

Capacitance distribution of {(Ni(0.6)Nb(0.4)(1-x)Zrx}(100-y)-Hy (x = 0.30, 0.35, 0.40, 0.45 and 0.50, 0 < or = y < or = 20) glassy alloy ribbons was carried out by ac impedance analysis at frequency of 1 kHz, in terms of a distributed constant equivalent circuit. The capacitance can be represented by oblique contour lines. The highest capacitance (1-11 microF) could be found near the point when x = 0.40, y = 10, which is a composition occurring room-temperature Coulomb oscillation, while capacitance of the composition (x = 0.35, y = 4) occurring ballistic transport was around 0.8 microF. The capacitance difference would be explained by an effect of hydrogen localization derived from morphology of distorted Zr-centered icosahedral Zr5Ni5Nb3 clusters and ideal Ni-centered clusters. The electrocapillarity equation showed that the specific capacitance between two electrodes increases parabolic with decreasing the distance, as a polarized glutinous liquid.

Experiments on solid-phase electrosurface migration through formally inert eutectic WO3|MeWO4 interfaces in symmetric electrochemical cells such as Pt|WO3|MeWO4|WO3|Pt are performed. It is shown that the most significant changes occur at the “cathode” interface (−)Pt|WO3|MeWO4|, where counter electrosurface drawing of WO3 to the inner surface of MeWO4 ceramics (with the formation of two-phase distributed composite WO3|MeWO4) and a much smaller flow of Me2+ components to the WO3 ceramics depth are observed. Scanning and transmission electron microscopy showed the formation of nano- and microscale objects of various shape in grain boundaries’ regions, among which well-faceted nanoobjects shaped as ribbons and rods from a few to hundreds of nanometers thick are noticeable. The Ca and Sr contents in WO3(−) cathode pellets after experiments in cells are determined by X-ray fluorescence analysis, scanning electron microscopy, energy-dispersive analysis, and depth profiling using glow-discharge spectrometry. The data obtained are interpreted based on the concepts of solid-phase electrocapillarity (WO3 migration) and electrochemical intercalation of Me into the WO3 structure.

A new model has been formulated for the electrochemical instability at the liquid∣liquid interface, for which only a rudimentary model [T. Kakiuchi, J. Electroanal. Chem. 536 (2002) 63–69] had been available. The new model considers the diffuse double layers in the presence of the specifically adsorbed surface-active ions, whose adsorption Gibbs energy linearly varies with the phase-boundary potential. The electrocapillary equation in the presence of the common ions partitioning in both phases is employed under the assumption that the partition of the surface-active ions is described by the Nernst equation. The excess surface charge due to the specific adsorption of surface-active ions is allowed for in calculating the structure of the diffuse part of the electrical double layers on both sides of the interface. The calculated electrocapillary curves agree with the experimental results. It is confirmed that electrocapillary curves can have positive curvature in a certain potential region, which signifies the presence of an instability window.

Electrocapillarity has been studied in detail at the interface between a hydrophobic ionic liquid (IL), trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, and water, where the ultraslow relaxation of the structure of the electrical double layer on the IL side of the interface exists. The response of the interfacial tension and that of the charging current to the potential step can be fitted by a double exponential model having the relaxation time constants of a few seconds and 100 s. The hysteresis in the interfacial tension in the IL diluted with nitrobenzene persists even in an almost 1:1 mixture of the IL and nitrobenzene. The thermodynamically definable double layer capacitance (C(dl)) estimated from the equilibrated electrocapillary curve, that is, the interfacial tension versus potential curve, at the IL|water interface has a maximum value of about 60 microF cm(-2) in the vicinity of the potential of zero charge (pzc) when the aqueous phase is 0.1 mol dm(-3) LiCl. The C(dl) versus the potential plot shows a characteristic camelback shape, showing a shallow minimum at the pzc, where the C(dl) value is 42 microF cm(-2). This minimum seems to reflect the contribution of C(dl) on the aqueous side of the interface to the total capacitance.

This paper describes highly efficient in-droplet particle concentration and separation where particles are concentrated and separated into droplets by traveling-wave dielectrophoresis (DEP) and subsequent electrowetting-on-dielectric droplet splitting. A successful concentration for 5-mum aldehyde sulfate (AS) latex particles was experimentally achieved using microfabricated devices, showing that 98% of the total particles were concentrated into a split daughter droplet. In addition, in-droplet particle separation was successfully achieved using the following two different cases of particle mixtures: case 1) a mixture of 5-mum AS latex beads and 8-mum glass beads; and case 2) a mixture of ground pine (GP) spores and 8-mum glass beads. In case 1), 97% of the total AS beads were separated into one split droplet and 77% of the total glass beads into the other split droplet. In case 2), over 92% of the GP spores were separated into a split daughter droplet, whereas 86% of the glass beads were separated into the other split daughter droplet. In all these concentration and separation experiments, the applied frequency and the conductivity medium are key parameters influencing the concentration and separation performance, which have been optimally determined by measuring the DEP and electrorotation spectra of the used particles prior to the concentration and separation experiments. This integrated in-droplet separation and concentration method may provide an additional functionality to digital microfluidics.

Large changes in stress (of order GPa) are observed with relatively modest variations in applied potential (on the order of 500 mV), even in nonspecifically adsorbing electrolyte solutions. Here we...

The electrochemical polarisation of metal catalyst films on solid electrolyte substrates can basically lead to three different effects: (a) the generation of mobile surface species (spillover) which spread over the catalyst surface and modify the catalytic activity, (b) potential-controlled segregation of impurities in the catalyst and (c) potential-dependent surface energy (electrocapillarity). The generation of spillover species occurs at the three-phase boundary between metal, solid electrolyte and gas phase and is highly localized. The spreading occurs via diffusion and leads to time-dependent and inhomogeneous surface concentrations. The kinetics of the spillover process can only be observed with in situ surface-analytical techniques in combination with electrochemical methods which offer sufficient resolution in space and time. Model experiments with UV and X-ray photoelectron emission microscopy (PEEM and SPEM) are summarized and discussed with respect to their relevance for the better understanding of electrochemical promotion in catalysis.

The electrocapillary curve and temporal stability of the interfacial tension were measured for a polarized flat water–dichloroethane interface under electrochemical instability. The interfacial tension was measured on the basis of capillary wave spectra obtained by means of the heterodyne detection of the light scattered at the interface. Anomalous behavior of the electrocapillary curve was observed in the potential range in which the electrochemical instability was expected. The correlation between the interfacial tension and the current spike observed in the chronoamperometry was examined. Despite the presence of the anomalous current spikes and other phenomena showing thermodynamic instability, the results revealed that the interfacial tension was stable and did not show any correlation with the anomalous current. The results were explained by a structure formation by the lateral mass transfer to avoid the instability, in addition to the vertical interfacial ion transfer which is apparently observed by the current measurement.

Nucleation and growth of electrochemically etched pores in Germanium (Ge) was investigated for n- and p-type Ge single crystals with {1 0 0}, {1 1 0}, and {1 1 1} orientations and doping concentrations of (10 14 –10 18 ) cm −3 . Various types of electrolytes, illumination conditions (front side, back side or none), and pre-treatments for optimizing nucleation were used. Several kinds of macropores could be obtained, mostly for the first time. In particular, pores could be obtained in p-type Ge samples. Pore geometries, morphologies, and growth peculiarities were found to be quite different from other semiconductors. Nucleation is generally difficult, the preferred growth direction is 〈1 0 0〉 or 〈1 1 1〉, stop planes are of {1 1 0} type, and there is always a strong electropolishing component compromising pore geometry and stability. Porous membranes have been produced showing electrocapillarity effects.

A thermodynamic framework has been provided for the interpretation of combined cyclic voltammetry and surface stress measurements, the latter being obtained from wafer curvature or beam deflection measurements of a solid electrode as a function of applied potential (so-called voltstressograms). Firstly, the derivation of electrocapillarity equations for solid electrodes has been critically reviewed by starting from the Gibbs adsorption equation appropriate for solid-electrolyte interfaces. This allowed us to demonstrate the critical importance of elastic surface strain in the thermodynamic boundary conditions of the partial derivatives intervening in the interpretation of voltstressograms. From these considerations, it was shown for the first time that the electrocapillarity equations for solid electrodes are not appropriate for describing the variation of surface stress with potential obtained from wafer curvature measurements, because such measurements are intrinsically incompatible with the constant strain condition implied in the electrocapillarity equations. An alternative explanation is provided for the experimentally observed proportionality between the current density, measured in cyclic voltammograms, and the first derivative of surface stress with respect to potential, obtained from voltstressograms.

The interfacial tension between the room-temperature molten salt (RTMS, also called ionic liquid) composed of 1-octyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide (C8mimC2C2N) and the aqueous solution containing 1-octyl-3-methylimidazolium chloride or lithium bis(perfluoroethylsulfonyl)imide has been measured as a function of the composition of the aqueous phase. The phase–boundary potential calculated for this non-polarized interface from the solution composition enables us to construct the corresponding electrocapillary curve, which shows a parabolic shape with respect to the variation of the phase–boundary potential over 300 mV. C8mim+ ions specifically adsorb at the interface. Switching of the potential-determining ion from C8mim+ to C2C2N− causes a jump of more than 160 mV in the potential at the outer Helmholtz plane on the aqueous side of the interface.

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

If two in each other immiscible liquids (one of them ionic solution) contact, then segregations at the interface occur and electric potential between both phases is generated. This is the case, e.g., when liquid metal contacts with liquid slag. Using electrochemical measurements the reaction course, reaction kinetics and adsorption mechanisms can be investigated. In chemical practice, current–potential dependencies of interfacial tension are frequently recorded. Their course and characteristic points deliver the information about the adsorption phenomena at the interface. Measurements using a.c. current and using nonstationary methods as, e.g., galvano or potentiostatic impulse, are applied to get more information about the nature of the adsorbed layers and the migration of ions near the interface. Electrochemical potential and electrochemical double layer are shortly discussed as well as the effect of adsorption on the electric potential and the interfacial tension. Finally some practical aspects of electrocapillarity phenomena are presented.

Contradictions between views on the nature of adsorbed species in HSO 4 − SO 4 2− systems are once again discussed. It is demonstrated that adsorbed HSO 4 − and SO 4 2− species cannot be distinguished on the basis of a method proposed earlier.

Electrochemical oscillatory phenomena have been observed in the redox reaction of the O 2 /O 2 − (superoxide ion) couple on a hanging mercury drop electrode (HMDE) in a limited aprotic medium. The current oscillation occurs during the reoxidation process of the electrogenerated O 2 − . It has been found that the observed oscillation is really irregular, complicated and affected by the addition of poly(vinyl chloride) as a maximum suppressor as well as many other experimental factors such as solvent, electrode substrate, concentration of O 2 − in the electrode vicinity and potential scan rate in cyclic voltammetry. The oscillation phenomena have been explained similarly to the maxima in classical polarography (i.e. by streaming phenomena) and in addition, based on the formation–destruction of a passive film on the electrode surface which results in the dissolution of the mercury electrode. The results obtained demonstrate that the electrogeneration and adsorption of O 2 − on HMDE are indispensable for the present oscillation.

This paper describes the development of a prototype pumping system with the potential for incorporation into miniaturized, fluid-based analytical instruments. The approach exploits the well-established electrocapillarity phenomena at a mercury/electrolyte interface as the mechanism for pump actuation. That is, electrochemically induced changes in the surface tension of mercury result in the pistonlike movement of a mercury column confined within a capillary. We present herein theoretical and experimental assessments of pump performance. The design and construction of the pump are detailed, and the potential attributes of this design, including the generated pumping pressure, flow rate, and power consumption, are discussed. The possible miniaturization of the pump for use as a field-deployable, fluid-delivery device is also briefly examined.

Total internal reflection fluorescence and electrocapillary measurements are employed to provide complementary potential-dependent information about the mechanical and photophysical properties of the interface between two immiscible electrolyte solutions, 1,2-dichloroethane-H2O. Adsorption of the zwitterionic amphiphile, di-N-butylaminonaphthylethenylpyridiniumpropylsulfonate (I) produces an interface with mechanical (interfacial tension) and charge transport properties qualitatively like the unmodified interface. Addition of dilauroylphosphatidylcholine (DLPC) to the organic phase produces an interface dominated by DLPC adsorption and drastically alters the potential dependence of the interfacial tension, gamma, the interfacial excess populations, GammaI, the charge transport, and the fluorescence response from I. This result is explained in terms of a potential-dependent protonation of the DLPC at the interface, which causes it to desorb, and a competition for interfacial sites between DLPC and protonated and unprotonated dye I. Protonation of DLPC results in a rise in gamma, which is correlated with an increase in transport of the organic-phase anion tetraphenylborate, TPB-, and an increase in interfacially excited fluorescence from I. Both results are explained by a model in which the mechanical properties of the interface, as determined by the interfacial DLPC population, direct the ability of other species to transfer across TPB- or adsorb to I the interface.

Interfacial tension and impedance measurements were used to study the electrochemical properties of the interface between 0.1 M LiCl in water and 0.05 M tetrabutylammonium tetraphenylborate in nitrobenzene in the absence and the presence of various tetraalkylammonium ions. While the presence of these ions has no effect on the interfacial tension, the interfacial capacity can be considerably enhanced. This enhancement appears to be an artefact arising from the inadequate representation of the interface or the electrochemical cell by the Randles equivalent circuit employed for impedance data analysis. Modifications to this equivalent circuit are discussed.

The present study deals with electrocapillarity effects in the three-phase system water−decane−polymer. This system consists of a decane droplet which adheres under water on a polymer surface. We applied an electric potential between an electrode beneath the polymer film and a platinum electrode immersed in the water. The polymer film acts as insulator: no steady electrical current flows between the electrodes. When the voltage is increased, the contact angle of decane and water changes, in some cases by up to 100°. The shape of the electrowetting curve (contact-angle cosine versus voltage plot) strongly depends on the type of the polymer. A saturation at higher voltages, connected with a hysteresis, is interpreted in terms of charge carrier injection into the polymer surface. Other deviations of the experimental results from the Lippmann−Young parabola concern a broadening with the polyolefins, a strong shift, and apparent reduction to one branch with two fluoropolymers, and for PET and a heavily oxidiz...

The electrocapillary equations and their application to solid electrodes are reviewed. Evidence is presented showing that solid electrodes exhibit two kinds of electrocapillary properties. For plastic deformation or immersion processes, thermodynamic properties of the solid electrodes are consistent with the classical Lippmann equation. For elastic processes, thermodynamic properties are inter-related by the Gokhshtein equation that accounts for the influence of elastic strain on a solid electrode’s charge density. The latter equation predicts the difference between the potential of zero charge and the potential of the maximum of the electrocapillary curve. For solid metals, the presence of the electronic dipole layer is the primary reason for the difference between these two points.

We studied the electrocapillary curves (ECC) σ(φ) of pure copper and copper doped with 0.05 mass% of sulfur at 1200°C in contact with boron + aluminium oxide electrolyte. A novel approach of the ECC determination involving in turn measurements of interfacial tension σ by capillary depression (CD), maximum pressure (MP) in a drop and X-ray survey of sessile drop (SD) methods was used. The highest accuracy was shown by the CD method, which was used in oxide systems for the first time.

Single-Pt nanoparticles (NPs) can be detected electrochemically by measuring the current-time (i-t) response associated with both hydrazine oxidation and proton reduction during individual Pt NP collisions with noncatalytic Hg- and Bi-modified Pt ultramicroelectrodes (Hg/Pt and Bi/Pt UMEs, respectively). At Hg/Pt UMEs, the i-t response for both hydrazine oxidation and proton reduction consists of repeated current "spikes" that return to the background level as Hg poisons the Pt NP after collision with the Hg/Pt UME due to amalgamation and deactivation of the redox reaction. Furthermore, at a Hg/Pt UME, the applied potential directly influences the interfacial surface tension (electrocapillarity) that also impacts the observed i-t response for single-Pt NP collisions for proton reduction that exhibits a faster decay of current (0.7-4 ms) to background levels than hydrazine oxidation (2-5 s). Because the surface tension of Hg is lower (-0.9 V), Pt NPs possibly react faster with Hg (amalgamate at a faster rate), resulting in sharp current spikes for proton reduction compared to hydrazine oxidation. In contrast, a stepwise "staircase" i-t response is observed for proton reduction for single-Pt NP collisions at a Bi/Pt UME. This different response suggests that electrostatic forces of negatively charged citrate-capped Pt NPs also influence the i-t response at more negative applied potentials, but the Pt NPs do not poison the electrochemical activity at Bi/Pt UMEs.

The surface tension σ of the yttrium scandium gallium garnet melt (the melting point is 2150 K) was measured by the method of tearing off the iridium probe from the melt surface. The temperature dependence of σ was determined in a nitrogen atmosphere at 0.6 atm in the range of melt temperatures of 2156 to 2218 K. Experimental data are presented as σ=1456+0.24 ( T -2156) dyn/cm. The measurements at different partial pressures of N 2 and O 2 were carried out at a melt temperature of 2156 K. Furthermore, the influence of electric field on the surface tension of YSGG melt was investigated. Experimental results are presented as dependence of σ versus current density.

Cystine in aqueous solutions reacts chemically with mercury, forming the surface-bound cysteine mercuric thiolate. When the potential of mercury is made less positive this compound is transformed (at a partially free mercury surface in a currentless process and at an occupied electrode under the passage of current) into cysteine mercurous thiolate. The latter compound is also formed in a reversible interaction of cystine with mercury in the potential range where cystine is adsorbed. At the negative end of this range the electroreduction of cystine occurs by the reduction of cysteine mercurous thiolate. At negatively charged mercury, where cystine is not adsorbed, two electrons are transferred directly to the cystine SS bond in an overall irreversible process. On the positive side the dissolution of mercury into solutions containing cystine starts by anodic formation of slightly soluble mercuric cystinate near the electrode surface.

Permeation of fluids (electrolytes and gases) in porous/particulate systems is important in batteries, fuel cells and other electrochemical reactors. A percolation model is proposed which describes the electrocapillary equilibrium in porous networks. Based on a set of doubly discrete non-linear difference equations, the local and global levels of flooding are numerically computed as a function of the bonds-filling factor p which incorporates system/input parameters such as electrode potentials, pressure differentials across fluid phase boundaries, electrocapillary characteristics and pore size distribution. A percolation threshold is identified at a value of p different from that corresponding to the infinite lattice. Differences between semi- infinite porous electrodes and infinite lattices are highlighted. The notion of a “flooded porous electrode” is sharpened. For non-wetting fluids, the possibility of an interesting transition is predicted which switches the porous electrode from a state of complete flooding to one of total evacuation. Related earlier works are discussed and several interesting future directions indicated.

The voltammetric behaviour of copper in the presence of marine hydrophobic organic matter and soil fulvic acid was examined by differential-pulse anodic stripping voltammetry (DPASV) in sodium perchlorate. These organic substances strongly adsorb on a mercury electrode, thereby affecting the peak current. The extent of this interference is related to the charge on the electrode during the plating step, but the mechanism of the influence on the anodic peak is mainly connected with the stripping step. A cathodic potential step whereby the effects of adsorption can be removed is described. This modified DPASV method was used to evaluate the lability of copper-organic complexes and to elucidate the effects on the anodic current due to the adsorption process.

The coadsorption of 3-methyl-isoquinoline (3-MeisoQ) and perchlorate ions has been examined at the mercury—aqueous solution interface by various electrocapillary methods. As a function of the surfactant and anion concentrations, three distinct superficial films have been characterized. At very negative potentials, the perchlorate ions are excluded from the condensed film formed by vertically oriented 3-MeisoQ molecules. At less negative potentials, a transition delimits a region of existence of a mixed film where the superficial organization differs only from that prevailing more negatively by the presence of the adsorbed perchlorate. The third film is present mainly in dilute solutions of 3-MeisoQ or perchlorate.

Double layer capacities and electrocapillary curves were measured for a mercury electrode in contact with eight solutions of sodium formate in water. The results confirm that the formate ion is very weakly adsorbed, making quantitative analysis of specific adsorption inaccurate. The effective dipole of the absorbed ion is very similar to that of other oxyanions such as NO3−, ClO4− and SO42−.

The absorption behavior of uracil at the mercury/electrolyte interface was studied by electrocapillary and capacitance measurements. Three different adsorption states (SI, SII, SIII) can be distinguished, depending on adsorbate concentration, temperature and potential. State I corresponds to a layer of adsorbed uracil molecules oriented flat on the electrode, which exhibits weak lateral interactions. The Frumkin isotherm is applicable. State II exhibits the properties of a 2-D condensed film. Based on a lattice—gas treatment an isotherm corresponding to the “low temperature series expansion” is applied. State III probably results from the formation of a multi-layer.

The apparent values of the standard ion-transfer rate constant k°app,i and charge-transfer coefficient αapp,i for ion transfer across the nitrobenzene—water interface at 25°C were measured using an ac impedance method for Me4N+, Et4N+, Pr4N+ and PF6− ions in aqueous solutions of LiCl at concentrations ranging from 0.01 to 0.8 mol dm−3. The change in the double-layer structure with LiCl concentration was deduced from the electrocapillary data. Taking account of the double-layer structure, we estimated the double-layer effect on the kinetic parameters within the framework of the classical Frumkin-type double-layer effect for the two types of current—potential characteristics for the ion transfer: the Butler—Volmer equation and the Goldman-type equation. The observed slight increase in k°app,i and the practical invariance of αapp,i with the LiCl concentration for all ions studied did not conform to the theoretical prediction from the Frumkin correction for both current—potential characteristics, suggesting that the contribution of the Frumkin-type double-layer effect on the observed values of the kinetic parameters is insignificant.

Meniscus heights on a gold flag electrode partially submerged in Li/K carbonate (62/38 mole percent) at 650°C have been determined under a variety of gas mixtures at atmospheric pressure. The meniscus height as a function of electrode potential shows a characteristic minimum for each gas composition and a relatively steep increase with increasing cathodic polarization. Analysis of the near‐equilibrium data, assuming electrocapillary effects only, shows that this is consistent with specific adsorption of oxide ion on the electrode. At appreciable polarization, mass‐transfer effects as well as adsorption appear to play a role, and the approach to steady‐state conditions following a disturbance is slow.

Cationic surface excesses of Li+, Na+, K+, Ca2+ and Mg2+ are derived from the electrocapillary curves of the interphase between mercury and their aqueous chlorides. They are compared with previously reported data on LaCl3 and AlCl3 obtained under similar conditions. The influence of cationic charge and size on the interfacial properties is discussed. While the solvent contribution to the surface excess is mainly determined by the size of the solvated cation, its charge appears to have a more relevant influence on the specific adsorption of chloride.

Interfacial effects produced in an immiscible liquid system by the action of an external electric field have been considered. The addition of small amounts of neutral phospholipids to the nonaqueous phase has been shown to result in a marked increase in the sensitivity of the interfacial boundary to the voltage applied, which is manifested by; (i) an accelerated decrease of the interfacial tension after the two immiscible liquid phases have been brought into contact; (ii) reduced interfacial tension, by 20–30 mN m , at the oil/water interface at field strengths of 1–10 kV m (the interfacial tension drop in the absence of phospholipids does not exceed 5 mN m ); (iii) development of electrohydrodynamic instability at the planar dividing surface between phases; and (iv) dispersion of water into the nonaqueous phase at smaller field strengths by a factor of about 100 as compared te those normally required in the absence of phospholipids. In order to gain a deeper insight into the mechanisms of interfacial phenomena, mainly exemplified by the n-heptane /water system containing phosphatidylcholine, three major issues have been considered: (1) Kinetics of the adsorption of phospholipid at the oil/water interface from the nonaqueous phase, and effects produced by exposure to an external electric field; also, the adsorption under equilibrium conditions, and the structure of the adsorption layer formed. (2) Interactions between neutral phospholipid and inorganic or organic ions at the interfacial boundary under the voltage applied. (3) Conditions for the occurrence of electrohydrodynamic instability at the dividing surface between oil and water and the formation of a water-in-oil emulsion; also aggregation and gelation processes induced in the nonaqueous phospholipid solution bulk by the action of a weak external electric field. Throughout the present paper, an attempt has been made to relate the microscopic behaviour ofphospholipids under an external electric field to macroscopically observable properties at the movable interfacial boundaries. The adsorption studies have shown that phosphatidylcholine is prone te self-organization into a liquid-crystalline state at an immiscible liquid interface. The disintegration of the interfacial lipid film thus formed by the action of a weak electric field has been explained as due to an enhanced electrohydrodynamic instability of liquid crystals. This results in the formation of either an emulsion, or a microemulsion in the nonaqueous solution bulk. The formation of a microemulsion is manifested by the appearance of an optically anisotropic gel, stable only under an external applied electric field, in the nonaqueous solution bulk. The noticeable drop in interfacial tension has been attributed to the formation of a microemulsion. The experimental evidence thus obtained has enabled us to suggest a mechanism for electrohydrodynamic instability and for the breakdown of the adsorption layer at the oil/water interface under the applied voltage. Further developments for research and potential practical application of interfacial phenomena, induced by an external electric field in phospholipid-containing immiscible liquid systems have been indicated, including their use for modelling processes in the living cell.

Stretch lengths of pure gold mono-atomic wires have been studied recently with an electrochemical scanning tunneling microscope (STM). Here, we will report a study of stretch lengths of gold mono-atomic wires with and without 1,6-hexanedithiol (HDT) using the STM break-junction method. First, the stretch length was measured as a function of electrode potentials of a bare Au(111) substrate and a gold STM tip in a 0.1 M NaClO4 aqueous solution. Second, a self-assembled monolayer (SAM) was fabricated on an Au(111) substrate by dipping the substrate into a 1 mM HDT ethanol solution. At last, we measured the stretch length of gold mono-atomic wires on a substrate covered with the SAM in place of the bare Au(111) substrate. We compared the electrode potential dependence of the stretch lengths of gold mono-atomic wires covered with and without HDT. We will discuss the effect of the electrode potential on the stretch lengths by taking account of electrocapillarity of gold mono-atomic wires.

This work presents an overview of electrochemical techniques, namely potentiometry, amperometry, tensammetry, electrocapillary measurements and biosensors, recently applied for the determination of surfactants.

This paper describes droplet manipulation and microparticle sampling where droplets driven by the electrowetting-on-dielectric (EWOD) principle are transported on perforated microfilter membranes and pick up microparticles in their path. Three designs of microfilter membranes that have different hole shapes (rounded rectangle versus circle holes), sizes (≥6 µm) and opening area ratios (5, 9 and 20%) are microfabricated and tested along with a commercial membrane (rounded rectangle holes of 60 µm × 128 µm, 17% opening area ratio). All the tested perforated membranes are embedded with a linear array of electrodes for EWOD actuation. Reversible EWOD actuations and droplet transportations are successfully achieved on the perforated filter membranes. Particle sampling is examined against glass particles (8 µm diameter and ~14° contact angle) and polystyrene particles (8 µm diameter and ~66° contact angle). It is demonstrated that as droplets are moved on the microfilter surfaces by EWOD actuation, they efficiently pick up the microparticles in their path, showing high sampling efficiencies: over 95% for the glass particles and over 85% for the polystyrene particles. This particle sampling method uses a small liquid volume (microliters or smaller) and has the capability of fully automatic handling. Thus, it is expected to be highly compatible and easily integrated with lab-on-a-chip systems for follow-up biological and chemical analyses.

The polyethylene capillary used for dropping mercury electrodes (D.M.E.) has permitted the study of interfacial tension by a drop time method in highly concentrated solutions. The electrocapillary curves were obtained for the aqueous solutions of KF, NaOH and KCL. The measurements evince that there is a difference between results obtained using glass and polyethylene capaillaries. The difference increases with the concentration of the electrolyte. We attribute that fact to wetting of the polyethylene capillary by mercury.

An electrocapillarity approach has been proposed in previous papers for electrochemical intercalation of H 2 SO 4 into graphite, which explains the high capacitive values (170 F/g) deduced from equilibrium potential charge curves or from low frequency a.c. impedance measurements (extending the double layer capacitance to the intercalated electrolyte — graphite interface). We propose here a similar view for GaCl 4 − intercalated (CH) x ; “switching” between doped and undoped (CH) x may correspond to the faradic like stage transformation of Graphite Intercalation Compounds (GIC), while a charging process of (CH) x chains with counter-ions recalls the capacitive “overcharging” of pure-stage GIC.

Electrocapillary phenomena has been investigated at high temperature for the contacts; liquid tin, lead, bismuth and indium with the solid electrolyte 0.92ZrO 2 − 0.08Y 2 O 3 . The existence of two maxima of interfacial free energy has been shown, as well as the dependence (in the case of tin and lead) of maximum interfacial free energy potentials on the type of single crystal face of the solid electrolyte which is in contact with liquid metal. It has been found that for tin and lead in the range 700–1000°C the potentials of the maxima of interfacial free energy depend on the temperature. It has been established that the second maxima, situated at more negative potentials, disappeared for tin at 1000°C and for lead at 900°C.

The conditions for obtaining the electrocapillary curves of the dilauroylphosphatidylcholine (DLPC) monolayer formed at the polarized nitrobenzene–water interface have been studied using the pendant drop method. To facilitate the measurement, the system for the interfacial tension measurement, including the computer software for the data handling, has been developed based on digital image processing of the video image of a pendant drop. The 95% confidence interval of the measured interfacial tension value was ±0.06 mN m−1. The time required to measure an electrocapillary curve with 30 points was 30 min, while the time necessary to convert the image data to the interfacial tension was 1 min. The potential drop across the monolayer has been demonstrated to influence the stability of the monolayer strongly. The DLPC markedly lowered the interfacial tension by forming a stable monolayer when the interface was polarized so that the aqueous phase has a negative potential with respect to the nitrobenzene phase. ...

The first phase of a systematic study of the electrochemical phenomena at the metal‐gas interface is presented. An experimental and theoretical analysis of the phenomenon of electrocapillarity at the metal‐gas interface is described. Experimental curves of the relative reduction of surface tension vs applied potential were obtained at the interface between a mercury electrode and vacuum or He, HBr, and ethanol at various bulk pressures. The electrocapillary curves resemble the theoretical electrocapillary curves obtained from first principles. The potential of the maximum surface tension is at zero voltage. At 4 kV the surface tension decreases significantly. The variation in the surface tension at this voltage is about 100 erg cm−2. The electrocapillary curve at the mercury‐He interface approaches the ’’vacuum’’ curve. The effect of ethanol involves an absolute depression of the surface tension, but the general shape remains the same as that of He. The HBr curve differs from all others due to surface rea...

Description d'un appareil completement controle par ordinateur pour des mesures de tension interfaciale a l'interface mercure/solution. Cet appareil est fonde sur la methode du temps de goutte, dont la reproductibilite et la precision sont ameliorees par une nouvelle technique d'etalonnage et l'emploi d'une electrode a goutte en polyethylene vitreux