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The thermodynamic method proposed in J. electroanal. Chem.309, 1, (1991) for analysis of adsorption data of organic compounds at electrified interfaces is extended to adsorption layers of two-state adsorbates. It is shown that the information which can be gained in such systems is considerably low in comparison with adsorption layers of constant-oriented adsorbates. Thus, the excess free energy of mixing and excess entropy cannot be calculated and only under optimum circumstances the Gibbs energies of adsorption and the particle-particle interaction parameter can be estimated. The thermodynamic method is applied to the study of the adsorption properties of 2- 3- and 4- methylpyridines on a mercury electrode form aqueous solutions of 0.1 N Na2SO4. It is shown that methylpyridines reorientate on the electrode surface from the flat state to the normal one with the N atom facing the solution. At potentials more negative than −0.7 V (sce) the reorientation of 2- and 3-methylpyridines is accompanied with a phase separation process. The Gibbs energies of adsorption and the particle-particle interaction parameter are estimated by means of the thermodynamic method and a correlation with interfacial interactions is attempted. Finally, the values of the interaction parameter are compared with theoretical calculations and discussed.

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 hydrodynamic flows which arise in the presence of mechanical vibrations of a capillary tube filled with immiscible liquids are investigated. At the hermetically sealed ends of the tube there are air bubbles. It is assumed that the interfacial contact perimeters of the immiscible liquids can slip relative to the walls of the tube. The results of numerical calculations are given for a mercury electrocapillary transducer [1–4], which is a capillary tube filled with water and mercury. The calculated and experimental amplitude—frequency characteristics (the dependences of the amplitude of the electric potential difference on the vibration frequency) are compared.

The macroscopic manipulation of liquids is a core component to the development of microfluidic devices. Although the Marangoni effect has been described for well over a century, actively tuning such surface tension effects is a more recent achievement. This Highlight compares recently reported electro- and photochemical methods in which this liquid manipulation has occurred. One such method, electrocapillarity as utilised by Prins et al., is shown in the picture.

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.

Electrically addressable variable-power optical elements of small (

Interfacial interactions between a hydroalcoholic solution of potassium hydrogen tartrate (KHT) and a stainless steel surface are studied, when an electrical potential is applied to the metal substrate. The capacitive domain of the metal–solution interface is determined by cyclic voltammetry. In order to study the influence of the potential on KHT nucleation and crystal adhesion, the solid–liquid interfacial energy is assessed from contact angle and capillary rise measurements. Experimentally, the contact angle between a NaF solution and a stainless steel vs. the potential has a parabolic behaviour. The metal topography has no apparent influence on physicochemical properties of the interface when ethanol is present in a KHT solution. The metal substrate promotes the formation of KHT crystals, which is improved by the application of an anodic potential. The adhesion of crystals becomes more effective when wires of 25 μm diameter are used in comparison with those of 250 μm.

Results are presented here on interfacial tension studies aqueous lithium chloride solution and tetrabutylammonium tetraphenylborate solution in nitrobenzene as functions of concentration and the potential difference applied to the interface. The experimental interface tension values were used to calculate relative suface excess values and then to determine the isotherm adsorption. The effects of various corrections for the drop shape in the separation moment and for incomplete drop separation on the interfacial tension value are discussed.

A cationic polyacrylamide was examined using polarography, constant potential coulometry, photon correlation spectroscopy, electrocapillarity and potentiometric titrimetry. A polarographic response was found in differential-pulse polarography (DPP), direct-current and Kalousek modes at −1,7 V versus a silver/silver chloride electrode. In each case the magnitude of the response was a function of polymer concentration. However, it is thought that the response is not due to the polymer itself but impurities found with it. These were found to have a pK of 4,75. The polymer appears to develop a more open structure in LiCl solution (

The influence of binary organic solvents on the double-layer structure has been analysed for a mercury-solution interface without detectable specific ionic adsorption. Electrocapillary curves and the differential capacity were measured for 0.01 M and 0.1 M KPF6 solutions in a number of acetone + methanol mixtures covering the complete range from pure methanol to acetone. The electrocapillary maximum (ECM) in pure acetone is shifted in the positive direction compared with that in methanol. Similarly, the interfacial tension at the ECM in acetone is lower by 5.5 mN/m than in the 0.1 M KPF6 methanolic solution. Acetone is selectively adsorbed more strongly on mercury, particularly on the cathodic branch of the capacity or the electrocapillary curves. As previously observed in the literature for the KPF6 ion in acetone, the capacity peak appears very close to the limit of positive polarization in methanol + acetone mixtures, as well as in pure methanolic solutions.

The adsorption behaviour of 2-thiouracil at the mercury/electrolyte interface was investigated by electrocapillary and capacitance measurements. Depending on adsorbate concentration, temperature and potential, three different adsorption regions can be distinguished (SI, SII, SIII), which are discussed quantitatively. State I corresponds to a layer of adsorbed 2-SU molecules, oriented flat on the electrode, which exhibits weak lateral interactions, but strong interactions with the positively charged electrode via the sulphur atom. State II exhibits the properties of a 2D condensed film and is characterized thermodynamically by application of a modified lattice-gas treatment. State III probably results from the formation of a partially covalent bond between 2-SU and mercury.

Standing waves have been parametrically excited on an interface between mercury and aqueous salt solutions by periodic electrical polarization of the interface. The waves obey the known dispersion relation for capillary‐gravity waves. The variation of the interfacial tension with the bias voltage across the interface has been measured, and displays the expected quadratic dependence. Various aspects of the excitation mechanism are shown to be in accord with theoretical expectation.

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.

Interfacial adhesive failure of a pipeline coating was found to be related to the operating temperature of the pipeline, the presence of moisture at the coating/steel interface and cathodic polarisation of the steel. The application of cathodic protection was found to be more detrimental to a pipeline coating than was the immersion of the coating specimens in alkaline environments without polarisation. It is suggested that in the system examined cathodic disbondment is initiated at a coating holiday by the electrochemical reduction of Fe3O4 in the interfacial oxide film and that propagation of the disbondment is associated with electrocapillary action which reduces the surface tension between the steel and the crevice solution. This process increases the thermodynamic disbonding force between the adhesive and the steel in the aqueous environment.

International audience; Herein, we study the viscoelastic response of concentrated salt solutions using surface waves excited by electrocapillarity. We show that the hydrodynamic behaviour of the solutions is similar to that of water at concentrations up to 2M-well above the concentration C*, at which inhibition of bubble coalescence occurs in these solutions, This result excludes the occurrence of changes in the slip conditions at C*, postulated to explain this inhibition. Our study is carried out on salts that both increase and decrease the surface tension. We observe that the salt that decreases the tension does not change the surface behaviour at all whereas the other two salts essentially produce negative contributions to the surface viscoelasticity at very high salt concentrations. The effects observed are quite large and remain to be explained.

A method is introduced for determining the zeta potential of planar surfaces by combining electroosmosis and capillarity. In this method, an electric field is applied across the channel, which is filled with aqueous solution seeded with fluorescent tracer particles. Some excess liquid is applied on both ends of the channel, which bulges out and modulates the capillary force across the channel by adjusting its curvature. While the velocity profile in the channel approaches steady state, a balance of the electroosmotic stress and Laplace pressure difference is achieved across the channel. However, as soon as the electric field is turned off, a Poiseuille flow develops in the channel due to the difference in the curvatures of the liquid bulges. We show that the measurement of the centerline velocity of the liquid inside the channel is enough to deduce the zeta potential of the surface. Utilizing this technique, the zeta potential of a hydrophobic glass surface (silanized by n-hexadecyltrichlorosilane, HC-16) has been measured to be -52.2 +/- 7.7 mV in distilled deionized water, which is in close agreement with the literature values. This technique has also been used to estimate the zeta potential of the HC-16 surface (zeta w(HC-16)), in the presence of the aqueous solutions of polyoxyethylene (23) lauryl ether (Brij 35). The zeta potential here at first becomes more negative than that in pure water, it stays flat for a while, and then it continues to become less negative as the concentration of the surfactant increases above the critical micelle concentration (CMC). This effect, where changes take place beyond the CMC but not below it, leads to a complementary Gibbs plot, where all the changes occur below the CMC but not above it. It is conjectured that the scavenging of hydroxyl ions by the Brij 35 micelles may be responsible for the observed effect.

Electrical actuation of liquid droplets at the microscale offers promising applications in the fields of microfluidics and lab-on-chip devices. Much prior research has targeted the electrical actuation of electrically conducting liquid droplets using dc voltages (classical electrowetting). Electrical actuation of conducting droplets using ac voltages and the actuation of insulating droplets (using dc or ac voltages) has remained relatively unexplored. This paper utilizes an energy-minimization-based analytical framework to study the electrical actuation of a liquid droplet (electrically conducting or insulating) under ac actuation. It is shown that the electromechanical regimes of classical electrowetting, electrowetting under ac actuation and insulating droplet actuation can be extracted from the generic electromechanical actuation framework, depending on the electrical properties of the droplet, the underlying dielectric layer and the frequency of the actuation voltage. This paper also presents experiments which quantify the influence of the ac frequency and the electrical properties of the droplet on its velocity under electrical actuation. The velocities of droplets moving between two parallel plates under ac actuation are experimentally measured; these velocities are then related to the actuation force on the droplet which is predicted by the electromechanical model developed in this work. It is seen that the droplet velocities are strongly dependent on the frequency of the ac actuation voltage; the cut-off ac frequency, above which the droplet fails to actuate, is experimentally determined and related to the electrical conductivity of the liquid. This paper then analyzes and directly compares the various electromechanical regimes for the actuation of droplets in microfluidic applications.

Two primary methods for electrostatically actuating microdroplets in channels currently exist: dielectrophoresis (DEP) for electrically insulating fluids and electrowetting on dielectric (EWOD) for conducting fluids. In each case, a transverse electric field is used to create an electrostatic pressure, giving rise to the transport of individual liquid slugs. This paper examines the nature of the force distribution for both EWOD and DEP actuated droplets. The effects of system parameters such as contact angle and electrode length on the shape of the force density and its net integral are considered. A comparison of the scaling properties of DEP and EWOD for applications in digital microfluidics is presented. The net DEP force is shown to be strongly peaked when a droplet interface is located near the edge of a charged electrode and reduces to the well-known lumped parameter model in the appropriate limits. The effect of electrode spacing is seen to have an inversely proportional effect on the force experienced by the droplet, and the effect of increasing droplet contact angle is observed to increase the net force on the droplet.

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.

Electrocapillary methods for excitation of capillary-gravitational waves at liquid surfaces have been modified for application to liquid-liquid interfaces. The necessary experimental modifications are described. Typical results are presented for a water-hexadecane interface. The observed propagation of the generated waves accords with theoretical expectation.

The electrocatalytic reduction of CO 2 on mercury with Ni(II)-cyclam was studied in detail by cyclic voltammetry, polarography and electrocapillarity of aqueous solutions with and without the catalyst under N 2 , CO and CO 2 . It is concluded from these electrochemical measurements that (i) the adsorbed complex (Ni(I)-cyclam ad ) on Hg, not the reduced complex in solution Ni(I)-cyclam, is the active catalyst for the CO 2 reduction; (ii) both Ni(II)- and Ni(I)-cyclam can adsorb on Hg, and the oxidation states of the adsorbed complexes depend on the electrode potentials; (iii) Ni(I)-cyclam adsorbs on Hg even at −2.0 V (vs. SCE) under N 2 , but the surface concentration of Ni(I)-cyclam ad decreases gradually with a decrease in the potential and desorbs completely at potentials more negative than −1.7 V under CO or CO 2 ; and (iv) the desorption of Ni(I)-cyclam ad under CO or CO 2 is due to the formation of unadsorbable Ni(I)-cyclam-CO by the reaction of Ni(I)-cyclam in solution with dissolved CO or electrocatalytically generated CO from CO 2 .

Les proprietes dynamiques des polymeres a l'interface eau/toluene sont etudiees par diffraction a ondes electrocapillaires

L'electrocapillarite et les proprietes d'adsorption de l'acide camphor-10-sulfonique sur une electrode de mercure dans des solutions d'electrolytes (Na 2 SO 4 , LiClO 4 , KNO 3 , KCl, KBr) sont etudiees

Electrocapillarity has been studied both theoretically and experimentally in the class of liquids which include palm oil. Numerical results are presented for palm oil. The theory predicts the surface tension to be proportional to the square of the electric field intensity. However, the exponent of the electric field intensity obtained from experiment is 1.90. The results also show that the surface tension increases monotonically at low fields and that nonlinearity is induced for a field intensity greater than 1.25*106 V m-1. The low-field dielectric constant is found to be 2.70.

The thermodynamic theory of electrocapillary phenomena at the interface between two immiscible electrolyte solutions is considered. A generalized electrocapillary equation for polarizable and reversible interfaces is derived based on Hansen's method. The Gibbs equation for electrolytic systems is obtained both in variables corresponding to ion concentrations and concentrations of neutral ion combinations. The relationship between the ion concentrations in the system and EMF of the circuit consisting of immiscible electrolyte solutions whose terminals are made of identical metals is discussed. The formulae for the thermodynamic charge and the free charge of the interface between two immiscible electrolyte solutions (ITIES) are analysed. The cases of both perfectly and ideally polarizable, and also reversible (non-polarizable) interfaces are considered. Relationship between thermodynamic charges in different sets of variables is obtained.

Dewetting is an industrial drying process by adsorption of surfactants at the solid/liquid interface. From dewetting tests, it was found that glass, with a highly negative charged surface, is dewetted instantaneously by cationic surfactants while a less charged surface takes a longer time or may not be dewetted at all. This implies that eletrostatic forces play an important role in adsorption and it was studied by electrocapillarity using mercury drop times versus the applied potential using a modified Regula Falsi computer program. Amphoteric surfactant, Sarkosyl O, adsorbs at the dropping mercury eletrode at moderate cathodic and anodic potentials only. At more extreme potentials, there is an increase in competition from the much more prevalent water dipoles and the coulombically attracted supporting elecrolyte, eventually displacing the surfactant. Anionic surfactant, Aerosol OT, starts being adsorbed at a moderate cathodic potential. After reaching a maximum at around the point of zero charge, adsorption remains relatively constant as the potential is increased in the anodic branch. Desorption does not occur, as in the case of the amphoteric surfactant, because the coulombic attractive forces of the anionic surfactant and the supporting electrolyte are equal in magnitude. Cationic surfactant, didodecyldimethylammonium nitrate, behaves unexpectedly when compared to Aerosol OT as the interfacial pressure decreases back to zero in the extreme cathodic branch. Detailed study of a homologous series of quaternary ammonium surfactants show a condensed liquid film and a solid film are formed at the interface. Further study of the cationic surfactant, using the surface enhanced Raman scattering technique, shows that maximum intensity for peaks of the CH2, stretches and scissoring were found at high negative potential. All these results indicate that cationic surfactants interact so strongly with negatively charged surfaces that the polar head group of the surfactant loses its lateral repulsion. At high negative potential, the formation of the surfactant monolayer (solid type) at the interface accounts for the decrease in interfacial pressure in electrocapillary experiments.

The specific interaction of N-tetradecylisoquinolinium (C(14)Iq+) with Cl- and Br- has been detected in the voltammetry of ion transfer and electrocapillarity at the interface between an aqueous solution (W) and a room-temperature ionic liquid (RTIL), N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide ([C(14)Iq+][C(2)C(2)N-]). This specific interaction also makes the transfer of Cl- and Br- into [C(14)Iq+][C(2)C(2)N-] energetically more favorable in comparison with that of F- and SO(4)(2-). The width of the polarized potential window in ion-transfer voltammetry at the [C(14)Iq+][C(2)C(2)N-]|W interface is significantly narrower because of the transfer of anions from W to RTIL. The degree of affinity of the anion with C(14)Iq+ agrees with the Hofmeister series. Such an ion-pair formation of anions in W with cations in the RTIL is much weaker when the cation constituting the RTIL is a symmetric tetraheptylammonium ion.

Experiments to measure the effect of applied electric fields on the surface tension of aqueous solutions are difficult and have so far proved inconclusive. The effect of fields on both the surface pressure and surface excess of adsorbed solutes can be calculated from the simpler measurements of surface potential, using Maxwell relations from a thermodynamic analysis of the Volta effect. Examples for the air/water interface of NaCl and sodium dodecyl sulfate solutions are given. The results are compared with data for insoluble spread monolayers and contrasted with electrocapillarity. The effect of electric fields on the surface tension of water itself remains obscure.

We report the observation of electrochemical actuation in growing dendritic fibers made of self-assembled copper nanostructures (of 100 nm or less in diameter), on the metallic cathode of an ordinary aqueous electrochemical cell. This could be achieved when a copper anode and another metal cathode is placed in aqueous solution of either dilute HCl or CuSO 4 , or CuCl 2 , or H 2 O, and upon application of a DC voltage in the range of 1.5-12.0 V. The actuation could be observed with an on-off cycle of the applied voltage in the above range. The phenomenon was also observed with the growth of bimetallic structures using a number of electrolytes such as Ag(NO 3 ), Pb(NO 3 ) 2 , CoCl 2 , NiCl 2 , CdCl 2 , ZnCl 2 , and HAuCl 4 . The fibrous structures remained stretched as they grew longer with time in the presence of an applied voltage. The extent of actuation was dependent on the applied voltage, the concentration of Cu 2+ ions in the solution, and also on ions such as Na + , which did not get deposited at the cathode. The observed phenomena under different conditions have been explained on the basis of electrocapillarity.

We propose and demonstrate a novel liquid based deformable mirror (LDM). The proposed LDM consists of an array of vertically oriented open capillary channels immersed in a pool of two immiscible liquids. A free-floating thin reflective membrane serves as the reflecting surface. By means of jet action, membrane deformation is induced. The control of jet flow through each channel is achieved by electrostatic means. This individual control enables the generation of complex surface profiles useful for adaptive optics applications. The advantages of this device include high stroke dynamic range, low power dissipation, high number of actuators, fast response time, and reduced fabrication cost. The device, however, can only be operated in a vertical orientation and is suitable for dynamic wavefront correction. A proof of principle of the device using an array of linearly addressed capillary channels is presented. Preliminary measurements showed that the response time is several milliseconds with a stroke of more than 10 microns. The design and fabrication of a prototype with around 100 actuators is in progress.

Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects¿rather than a unique one¿are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.

We present the first set of results measuring the change in interfacial free energy and surface stress for Au(111) electrodes in an electrolyte containing a nonspecifically adsorbing anion and compare this behavior to that in an electrolyte containing an anion known to undergo specific adsorption. Generally, we find that the surface stress is more sensitive to changes in electrode potential and adsorption then the interfacial free energy. The results obtained in fluoride electrolytes are compared to the predictions of a thermodynamic analysis.

We report a simple approach to actively control the formation of the self-assembled colloidal crystals in the microfluidic networks using a combination of electrocapillary forces and evaporation-induced self-assembly. Using this scheme, we can not only selectively fabricate the colloidal crystals in the desired channels, but we can also build colloidal crystals with different optical properties in different channels or in the same channel.

At the heart of the laboratory on a chip are chemical or biochemical probes designed to detect specific molecules or reaction products. For these probes to perform their function, a microfluidic "plumbing system" is needed to accept samples, then manipulate, dispense, and distribute tiny liquid volumes on the chip. The most promising mechanisms for handling such small quantities of liquid -- from microliters down to tens of picoliters -- are all electrostatic, e.g., electrocapillarity, electroconvection, electrophores is, electro-osmosis, and dielectrophoresis. Despite years of study of these effects, the body of existing work is an imperfect guide to their effective exploitation in microfluidic applications. Attempts to harness electrostatic forces in structures

Mechanical strains at liquid- and polyethylene-metal electrode interfaces were detected using an interferometric method. The results indicate that the mechanical stresses at the interfaces can be expressed in terms of the Gibbs adsorption equation. Measurements on a variety of dielectric-metal systems suggest that all dielectric interfaces under electrical stress normal to the interface will be subjected to tangential mechanical stress and subsequent strain. Under alternating applied fields the stresses are cyclic and, in solid dielectrics in particular, could lead to stress cracking and other fatigue phenomena. The processes might be particularly significant in the strong fields encountered in high-voltage cables. Moreover, since similar processes operate at liquid-dielectric interfaces, these Gibbsian electrocapillarity effects can be expected to have an important role in water-tree inception and growth in cables. >

For an ideally polarizable electrode it is found that among numerous volume Hansen excesses there exists one which is correlated with the Archimedes law and plays the role of the solution volume displaced due to occurrence of surface layer. This volume excess could be called the Archimedes volume excess or the Archimedes volume of the surface. The Archimedes volume of the surface can be expressed in the form of a partial thermodynamic derivative.

Using a generalisation of the theory of electrocapillarity, it is shown that an electrical field E in a dielectric liquid will generate a mechanical tensile stress /spl epsi/ E/sup 2/ which is everywhere orthogonal to the electrical field. For fields between 10/sup 8/ and 10/sup 9/ V m/sup -1/ the mechanical stress is sufficient to enhance significantly the thermal generation of sub-microscopic cracks (holes) in the liquid. When the hole concentration is large enough, the same stress will encourage the propagation of cracks through the liquid by the Griffith's process which is well known for the fracture of solids. Streamer growth is considered in terms of this mechanical model and it is suggested that electrical discharges have a secondary rather than a primary role in the process.

This review summarizes our on-going effort to establish surface tension as a useful force for MEMS, especially microfluidics. Presented are several examples of using surface tension for microdevices. Droplet ejection mechanism using bubble check valve, pumping with sequential bubbles in microchannel, and electrostatic switching of liquid-metal droplet demonstrate how surface tension attenuates liquid movement so effectively in microscale. Liquid pumping using a bubble (or a droplet) under thermal gradient and electrically driving liquid-metal droplets in microchannel demonstrate that surface tension can even be used an an attractive driving force for microactuation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Langmuir-Blodgett films (LB-films) consist from few LB-monolayers which are high structured nanomaterials that are very promising materials for applications. We use a geometrical approach to describe structurization into LB-monolayers. Consequently, we develop on the 1-jet space J 1 ([0,∞),R 2 ) the single-time Lagrange geometry (in the sense of distinguished (d-) connection, d-torsions and an abstract anisotropic electromagnetic-like d-field) for the Lagrangian governing the 2D-motion of a particle of monolayer. One assumed that an expansion near singular points for the constructed geometrical Lagrangian theory describe phase transitions to LB-monolayer. Trajectories of particles in a field of the electrocapillarity forces of monolayer have been calculated in a resonant approximation utilizing some Jacobi equations. A jet geometrical Yang-Mills energy is introduced and some computer graphic simulations are exposed.