Concentrating particles on drop surfaces using external electric fields

We propose to use an externally applied uniform electric field to alter the distribution of particles on the surface of a drop immersed in another immiscible liquid. Specifically, we seek to generate well-defined concentrated regions at the drop surface while leaving the rest of the surface particle free. Experiments show that when the dielectric constant of the drop is greater than that of the ambient liquid the particles for which the Clausius-Mossotti factor is positive move along the drop surface to the two poles of the drop. Particles with a negative Clausius-Mossotti factor, on the other hand, move along the drop surface to form a ring near the drop equator. The opposite takes place when the dielectric constant of the drop is smaller than that of the ambient liquid, namely particles for which the Clausius-Mossotti factor is positive form a ring near the equator while those for which such a factor is negative move to the poles. This motion is due to the dielectrophoretic force that acts upon particles because the electric field on the surface of the drop is nonuniform, despite the uniformity of the applied electric field. Experiments also show that when small particles collect at the poles of a deformed drop the electric field needed to break the drop is smaller than without particles. These phenomena could be useful to concentrate particles at a drop surface within well-defined regions (poles and equator), separate two types of particles at the surface of a drop or increase the drop deformation to accelerate drop breakup.     

Development of a new methodology to study drop shape and surface tension in electric fields

Development of a new methodology for the study of both shape and surface tension of conducting drops in an electric field is presented. This methodology, called axisymmetric drop shape analysis-electric fields (ADSA-EF), generates numerical drop profiles in an electrostatic field, for a given surface tension. Then, it calculates the true value of the surface tension by matching theoretical profiles to the shape of experimental drops, using the surface tension as an adjustable parameter. ADSA-EF can be employed to simulate and study drop shapes in the electric field and to determine its effect on liquid surface tension. The method can also be used to measure surface tension in microgravity, where current drop-shape techniques are not applicable. The axisymmetric shape of the drop is the only assumption made in the development of ADSA-EF. The new scheme is applicable when both gravity and electrostatic forces are present. Preliminary measurements using ADSA-EF suggest that the surface tension of water increases by about 2% when an electric field with the magnitude of 10(6) V/m is applied.     

Devitrification of aluminosilicate glasses under applied electric fields

The effect of electrolysis on the devitrification of aluminosilicate glasses containing 2–10 wt. % Ti, V, Fe, Co and Ni was studied by DTA. In all cases the devitrification temperature is lowered under electrolysis by an amount greater than that which would be achieved by independently electrolysing or doping with the transition metal ion. The relative effect of the different transition metal ions on devitrification is explained in terms of the strengths of the respective metal-oxygen bonds and the octahedral/tetrahedral site preferences of the ions. The electrolysis mechanism is similar to that of the undoped base glass, but also includes migration of the transition metal ions to the cathode and the possibility of interaction between these species and the residual protons of the base glass.

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Zusammenfassung Der Einfluß der Elektrolyse auf die Entglasung von Alumosilikatglas-Arten mit 2 bis 10 Gew.% Ti-, V-, Fe-, Co- und Ni-Gehalten wurde mittels DTA untersucht. In allen Fällen wird die Entglasungstemperatur stärker herabgesetzt als bei unabhängig durchgeführter Elektrolyse oder Zusatz des Übergangs-Metall-Ions. Die relative Wirkung der verschiedenen Übergangs-Metall-Ionen wird aufgrund der Stärke der betreffenden Metall-Sauerstoff-Bindungen und des Vorrangs der tetraedrischen bzw. oktaedrischen Stellen der Ionen erklärt. Der Mechanismus der Elektrolyse ist ähnlich wie bei Gläsern ohne Zusatz, umfaßt aber auch die Wanderung des Übergangs-Metall-Ions zur Kathode und die Möglichkeit der Aufeinanderwirkung dieser Arten und der Restprotone des Grundglases.

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Résumé On a étudié par ATD l'effet de l'électrolyse sur la dévitrification de verres types aluminosilicates contenant 2 à 10 % en poids de Ti, V, Fe, Co et Ni. Dans tous les cas la température de la dévitrification est abaissée d'une manière plus importante sous électrolyse que si celle-ci est effectuée indépendamment ou que par dopage par des ions des métaux de transition. L'effet relatif des divers ions des métaux de transition s'explique en termes de forces des liaisons respectives du métal et de l'oxygène ainsi que par la préférence des ions pour les sites octaédriques ou tétraédriques. Le mécanisme de l'électrolyse est similaire pour les verres sans additifs. Il comprend cependant aussi la migration de l'ion du métal de transition vers la cathode et la possibilité de l'interaction de ces espèces avec les protons résiduels du verre de base.

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, 2–10 Ti, V, Fe, Ni, . , , . - / . , , .

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We are indebted to Professor J. F. Duncan for advice and helpful criticism, Mr. R. A. Kennerley for the use of the thermal analyser, Dr. G. Challis for the electron microprobe analyses and Mr. G. D. Walker for the scanning electron microscopy.     

Devitrification of aluminosilicate glasses under applied electric fields

Journal of Thermal Analysis and Calorimetry - Electric fields have been shown by a combined DTA-electrolysis technique to decrease the temperature of the exothermic devitrification of...     

Water absorption in polyethylene under external electric fields

Monte Carlo simulations of the solubility and structure of water in polyethylene in thermodynamic equilibrium with liquid water were performed in external fields ranging from 2 x 10(5) to 4 x 10(9) V/m. For a given equilibrium temperature and pressure, the water solubility decreases at higher fields. This occurs since it is energetically favorable for water molecules to be in the pure water phase than in the polyethylene matrix at high field strengths, and results in an increased density in the water phase. However, fields relevant to high voltage conduction (in the absence of defects that can lead to large local field strengths) do not change the solubility. In addition, at large fields the number of water clusters decreases for all cluster sizes. The rate of decrease is highest for large clusters, and a larger fraction of water molecules exist as monomers in the polyethylene matrix at high fields. Large fields also cause alignment of the water molecules, which leads to more clusters with linear topologies and hence an increase in the cluster radius of gyration.     

Deformation and motion of a charged conducting drop in a dielectric liquid under a nonuniform electric field

As a tool for transporting a drop inside another fluid, a charged conducting drop driven by Coulombic force is considered. Specifically, deformation and motion of a charged conducting drop under nonuniform electric fields are studied using the perturbation method. For simplicity in analysis, the applied electric field is assumed to be expressed as the sum of a uniform field and a linear field and the flow is assumed to be in the Stokes flow range. The deformed drop shape due to electrical stress is computed to the first order of the electrical Weber number (W). Then the electric force and the hydrodynamic drag are computed to derive the formula of the translation velocity, which is valid up to O(W). Several important results have also been obtained for the effect of drop deformation on the electric and hydrodynamic forces exerted on the drop.     

Capillary electrophoretic separation of dsDNA under nonuniform electric fields

Improved sensitivity for the analysis of DNA by capillary electrophoresis has been achieved, based on simultaneous increases in optical path length and injection volume. To increase the optical path length, bubble cells with diameters ranging from 150 to 450 microm have been fabricated and tested. In terms of resolution and sensitivity, a bubble cell of 300 microm diameter is appropriate when using 75-microm capillaries. To allow greater injection volumes, we performed on-line concentration of DNA in the presence of electroosmotic flow (EOF) using 2.0% poly(ethylene oxide) (PEO). With a 300-microm bubble cell, a 170-fold improvement in the sensitivity for the 89-bp fragment has been accomplished when injecting about 0.33 microL DNA. In the presence of the bubble cell, the resolution for the large fragments improves while that for the small ones (<124 base pair) decreases. The effect of bubble cells was further investigated by conducting DNA separation in the absence of EOF, showing that improvements in resolution are mainly due to increased migration differences when DNA migrated at low electric field strengths in the bubble region. We have suggested that such an effect is more profound using shorter capillaries, leading to complete separation of phiX 174 RF DNA-Hae III digest in 2 min.     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields

The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation to-Fe₂O₃ was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe₃O₄ and FeO at the expense of Fe₂O₃ is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

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Zusammenfassung Der Einfluß eines elektrischen Feldes auf die thermische Dehydratisierung des amorphen hydratisierten Eisen(III)oxids in oxidierenden, inerten und reduzierenden Atmosphären wurde durch Röntgendiffraktometrie untersucht. In oxidierenden und inerten Atmosphären wurde die Umwandlung zu -Fe₂O₃ durch elektrische Felder gefördert, besonders an der negativen Elektrode. Die Form der Kristallite des Produkts war ebenfalls an der negativen Elektrode am größten. Beide Ergebnisse werden durch die Proteinwanderung zur negativen Elektrode erklärt, wo diese Wasser bilden, das für die kristalline Phase als Keimbildner fungiert. In reduzierenden Atmosphären wird die Bildung von Fe₃O₄ und FeO auf Kosten von Fe₂O₃ durch elektrische Felder besonders an der negativen Elektrode erleichtert. Mögliche Reaktionsmechanismen werden erörtert und die Rolle der Protonen bei der Stabilisierung defekt-spineller Zwischenstufen und Produkte besprochen.

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Résumé L'effet d'un champ électrique sur la déshydratation thermique de l'oxyde de fer(III) hydraté amorphe a été étudié par diffractométrie des rayons X, dans des atmosphères oxydante, inerte et réductrice. En atmosphères oxydante et inerte, le champ électrique facilite la transformation en -Fe₂O₃, en particulier à l'électrode négative. La taille des cristaux formés est également plus élevée à l'électrode négative où il se forme de l'eau qui agit comme agent de nucléation de la phase cristalline. En atmosphère réductrice, le champ électrique facilite la formation de Fe₃O₄ et FeO, aux dépens de Fe₂O₃, en particulier à l'électrode négative. On considère les mécanismes de réaction possibles et on discute le rôle des protons sur la stabilisation des produits et des intermédiaires défauts-spinelles.

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- (III) , . -Fe₂O₃ , , . , , . Fe₃O₄ FeO Fe₂O₃ . , .

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The author is indebted to P. J. Melling for assistance with the measurements in H₂/N₂ atmospheres.     

Crystallite growth in magnesium oxide under applied electric fields

An electrolysis cell is described for use in conjunction with a high-temperature X-ray furnace, which permits X-ray diffraction studies to be made of solids during the course of their high temperature electrolysis. The technique is applied to an investigation of the effect of electric fields on crystallite growth in MgO at 600°C in air, argon and reducing atmospheres. In all cases crystallite growth is greatest at the positive electrode face, suggesting that the charge carriers are anions. The efficiency of the electrolysis process depends both on the concentration of charge carriers and on the concentration of anion vacancies by which the charge carriers migrate. The defect concentration is increased under reducing conditions. In MgO samples containing a high concentration of protons, the conduction is protonic, with the greatest crystallite growth occurring at the cathode due to the catalytic action of the water vapour formed in that region by recombination of protons with hydroxyl ions.     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields,I

A method which has been developed for thermogravimetric study of solids in the presence of applied electric fields has been used in a study of kaolinite dehydroxylation in a controlled inert atmosphere. Electric fields of 10⁵ V/m lower the initiation temperature for dehydroxylation by as much as 60 in some cases; the activation energy for dehydroxylation is reduced by 3–12 kcal/mole. The rate constants for electrolysed samples (based arbitrarily on a first-order law) are increased by electrolysis but this effect falls off at higher temperatures as the normal thermal processes begin to predominate. The effect of the field on the various processes of ionic migration in the lattice is discussed.

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Zusammenfassung Eine zur thermogravimetrischen Analyse von Festkörpern unter Anwendung elektrischer Felder entwickelte Methode wurde zum Studium der Dehydroxylierung von Kaolinit in einer geregelten inerten Atmosphäre herangezogen. Elektrische Feldstärken von etwa 10⁵ V/m setzten die Anfangstemperatur der Dehydroxylierung in einigen Fällen sogar um 60 C herab; die Aktivierungsenergie der Dehydroxylierung wird um 3 bis 12 kcal/mol herabgesetzt. Die — willkürlich aufgrund einer Gesetzmäßigkeit erster Ordnung berechneten — Geschwindigkeitskonstanten der elektrolysierten Proben werden durch die Elektrolyse erhöht, doch fällt dieser Effekt bei höheren Temperaturen, wo er von den normalen thermischen Vorgängen überlagert wird, weg.Die Wirkung des elektrischen Feldes auf die verschiedenen Vorgänge der Ionenwanderung im Gitter wird erörtert.

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Résumé On a mis au point une méthode pour l'étude thermogravimétrique des solides sous l'action d'un champ électrique et on l'a utilisée pour suivre la déshydroxylation de la kaolinite en atmosphère inerte contrÔlée. L'application de champs électriques d'environ 10⁵ V/m abaisse la température initiale de la déshydroxylation de 60 C dans certains cas et l'énergie d'activation est réduite de 3 à 12 kcal/mol. On observe l'augmentation des constantes de vitesse des échantillons soumis à l'action du champ électrique (par rapport à une loi choisie arbitrairement du 1^er ordre) mais cet effet cesse aux températures élevées où les processus thermiques normaux deviennent prédominants.On discute l'influence du champ électrique sur les processus de migration d'ions dans la grille.

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. , 10⁵ V/m, , 60C; 3–12 /. ( ) , , .

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This work was supported by an S.R.C. Research Grant. The author is indebted to Dr W.T. Raines and Dr G. M. Fryer for helpful discussion.     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields,II

The effect of electric fields on the thermal dehydroxylation of Mg(OH)₂ (brucite) and Al(OH)₃ (gibbsite) have been studied by thermogravimetry in a controlled inert atmosphere. Electric fields exert no beneficial effect on the reaction of gibbsite; in some cases the reaction is slightly retarded. By contrast, a small but significant beneficial effect is observed in brucite, in which the initiation temperature and activation energy is lowered at field strengths of about 10⁵ V/m. The difference in behaviour of the two hydroxides is attributed to differences in the mobility of anionic defects and oxygen-containing “proton-transfer complexes”. The transport of the various protonbearing species in an electric field is discussed.     

Thermal reactions of inorganic hydroxy-compounds under applied electric fields,III

The energy level separation in symmetrical and unsymmetrical double minimum potentials in the presence of electric fields is calculated by first-order perturbation theory, from which the tunnelling probability of protons is obtained for both perturbed and unperturbed potentials. Tunnelling probability is slightly increased by fields of about 10⁵ V/m, but a greater increase in tunnelling probability occurs when a symmetric potential becomes unsymmetric. The tunnelling process is too rapid to account for observed differences in dehydroxylation behaviour of Al(OH)₃, Mg(OH)₂ and kaolinite under electrolysis. Estimates, from indirect evidence, of the rates of anion defect generation and annihilation support the theory that the rate-determining field-dependent process is the surmounting of anionic lattice vacancies by oxygen-containing species.

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Zusammenfassung Die Trennung des Energieniveaus in symmetrischen und unsymmetrischen doppelten Minimumpotentialen in Gegenwart von elektrischen Feldern wird mittels einer Störungstheorie erster Ordnung berechnet, aus welcher die Wahrscheinlichkeit der Tunnelbildung von Protonen für gestörte sowie ungestörte Potentiale erhalten wird. Felder von 10⁵V/m erhöhen die Wahrscheinlichkeit der Tunnelbildung in geringem Maße, eine bedeutendere Zunahme der Wahrscheinlichkeit der Tunnelbildung tritt jedoch auf, wenn ein symmetrisches Potential unsymmetrisch wird. Der Vorgang der Tunnelbildung ist zu schnell um die Unterschiede des Verhaltens von Al(OH)₃, Mg(OH)₂ und Kaolinit bei der elektrolytischen Dehydroxylierung zu erklären. Schätzungen der Geschwindigkeiten der Anionen-Defektbildung und -Vernichtung aus indirekten Angaben unterstützen die Theorie, daß der geschwindigkeitsbestimmende, feldbedingte Vorgang die Überdeckung der Lücken im Anionengitter durch sauerstoffhaltige Arten ist.

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Résumé La séparation des niveaux d'énergie des potentiels à minimum double, symétrique et asymétrique, se calcule à l'aide de la théorie des perturbations du premier ordre, à partir de quoi la probabilité de l'effet tunnel des protons s'obtient aussi bien pour les potentiels perturbés que pour les non perturbés. La probabilité de l'effet tunnel augmente quelque peu sous l'influence de champs d'environ 10⁵ V/m, mais une augmentation plus notable de cette probabilité apparaît quand un potentiel symétrique devient asymétrique. Le processus de l'effet tunnel est trop rapide pour rendre compte des différences de comportement observées pour Al(OH)₃, Mg(OH)₂ et la kaolinite lors de l'électrolyse déshydroxylante. Des estimations faites à partir de données indirectes pour connaître les vitesses d'apparition des défauts anioniques et celles de leur disparition, viennent à l'appui de la théorie suivant laquelle le processus dépendant du champ et déterminant la vitesse est celui de l'occultation des lacunes du réseau anionique par des espèces contenant de l'oxygène.

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. , . 10⁵V/; , . , Al(OH)₃, Mg(OH)₂ . , , .

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Part of this work was carried out under an S.R.C. research grant. The author is indebted to Dr. J.P.M. Bailey for advice on the quantum-mechanical calculations, Dr. W.T. Raines and Dr. P.G. Rouxhet for helpful discussion. and to Mrs. F. Jackson for the computing.     

Computational insights of two-dimensional infrared spectroscopy under electric fields in phosphorylcholine

Influence of static electric field in biological cells causes electroporation, which results in the increase of permeability of the cells and phospholipid bilayer. However, the precise mode of action of electric fields on phospholipid bilayer and their quantum mechanics are still unclear. Therefore, to understand the quantum-based biological effect, we aimed to study two-dimensional infrared (2D-IR) spectra-adopted quantum mechanics/molecular mechanics (QM/MM) simulations under the influence of static electric fields on Phosphorylcholine, an important component in phospholipid membrane. Initially, QM/MM studies were performed under the influence of electric field, ranging from −1.543 to 1.028 V/nm. A multilayer ONIOM model (in combination with DFT/B3LYP/6-31G [d, p] and DREIDING force fields) was used to obtain 2D-IR simulated spectra to calculate electrostatic interaction in the biological system. The results demonstrated that the phosphate group played an important role on α-rotation in LUMO and the chlorine atom had a major contribution in HOMO. In addition, decreased number of hydrogen bonds demonstrated that uncoupling reaction of the P-O stretching vibrations while the electric field was −1.542 V/nm. Moreover, we observed that the electric field is −1.028 V/nm, there is no rotational isomerization in phosphorylcholine. We concluded that the static electric fields significantly affect the anharmonic frequencies, vibration coupling and the structure of the phosphorylcholine.     

Switch chemistry at cryogenic conditions: quantum tunnelling under electric fields

While the influence of intramolecular electric fields is a known feature in enzymes, the use of oriented external electric fields (EEF) to enhance or inhibit molecular reactivity is a promising topic still in its infancy. Herein we will explore computationally the effects that EEF can provoke in simple molecules close to the absolute zero, where quantum tunnelling (QT) is the sole mechanistic option. We studied three exemplary systems, each one with different reactivity features and known QT kinetics: π bond-shifting in pentalene, Cope rearrangement in semibullvalene, and cycloreversion of diazabicyclohexadiene. The kinetics of these cases depend both on the field strength and its direction, usually giving subtle but remarkable changes. However, for the cycloreversion, which suffers large changes on the dipole through the reaction, we also observed striking results. Between the effects caused by the EEF on the QT we observed an inversion of the Arrhenius equation, deactivation of the molecular fluxionality, and stabilization or instantaneous decomposition of the system. All these effects may well be achieved, literally, at the flick of a switch.

Adding an external electric field to reactions driven by quantum mechanical tunneling brings a whole new dimension to the idea of switch chemistry.     

Polyaniline and its modification for electroresponsive material under applied electric fields

Polyaniline (PANI) and its various copolymers were synthesized using different monomers such as o‐methyl‐, o‐methoxy‐, o‐ethyl‐, o‐ethoxyaniline and sodium diphenylamine sulfonate by the chemical oxidation polymerization as air‐stable organic conducting polymers, and adopted as one of the most potential materials of electrorheological (ER) fluids, especially for the anhydrous system. A relatively low density, a controllable conductivity, and thermal stability are advantages of the PANI based ER system compared with other ER materials. An FT‐IR analysis was adopted to confirm their synthesis and a scanning electron microscopy (SEM) analysis indicated the shape of PANI derivatives was irregular. The effect of functional group of PANI on electric and electroresponsive properties of poly(aniline‐co‐ethoxyaniline) (COPA) particles were examined. A universal scaling equation of the yield stress was applied to these ER fluids and it was found that all data were collapsed successfully onto a single curve regardless of monomer type of the polyaniline synthesized. Copyright © 2005 John Wiley & Sons, Ltd.     

An in situ infrared study of magnesium hydroxide dehydroxylation under electric fields

A specially designed IR electrolysis cell is described, which allows samples to be simultaneously heated and electrolysed during the recording of their IR spectra. By means of this cell, changes in the intensity of the hydroxyl stretching band at 3670 cm^?1 were recorded as a function of temperature both in the presence and absence of an applied electric field. The intensity of the ?OH band decreases with temperature in two distinct stages, both of which are influenced by the electric field. The effect of the electric field on the regain of spectral intensity of the hydroxyl band on re-cooling the sample to room temperature was also studied, and the results discussed in terms of the delocalization of the protons from their respective molecules, possibly by a field-dependent tunnelling mechanism. The effect of the field on the shape and frequency of the ?OH stretching band is also discussed.     

Surface anchoring and the saturation behaviour of a NLC cell under external electric and magnetic fields

Based on the modified Rapini-Papoular formula for surface anchoring energy, the saturation behaviour of a weak anchoring nematic liquid crystal cell under electric and magnetic fields has been studied by the methods of analytical derivation and numerical calculation. The results show that the transition at saturation point may be second order, as many authors have predicted. However, it may also be first order. The condition for the first order transition is deduced; it is related to the anchoring parameters. The influence of anchoring on the saturation field strength is also discussed, both for second and for first orders; the results are shown by graphically.     

Molecules in electric fields

Finite field perturbation theory coupled with configuration interaction techniques have been used to evaluate the components of the polarisability tensor of H₂ at and near its equilibrium internuclear separation. The values are fitted to a polynomial which then yields the derivatives of the polarisability with respect to internuclear distance. Our results compare favourably with theoretical values obtained by the use of highly accurate correlated wavefunctions.     

Dynamics of a lipid bilayer induced by electric fields

The dynamics of a lipid bilayer of 1-palmitoyl-2-oleoyl-glycero-3-phospho-ethanolamine, POPE, is investigated under the effect of two electric field intensities. The box of 720 lipids and 13,458 water molecules-plus boundary conditions-undergoes similar re-organizational dynamics in the presence of fields of 0.35 V nm(-1) and 0.5 V nm(-1). Water fingers form followed by some lipid translocation from one layer to the other. The re-organization kinetics is of the second order and is roughly 5 times faster at the higher field. The translocations may occur also upon field switch off, provided that their duration was sufficiently long. Driving few lipid translocations by a macroscopic tool, such as the electric field, appears possible.     

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.