Applications of Electric Fields

Kabanov and Zingel [352] have recently published a comprehensive review of studies of the effect of application of continuous or periodic electric fields on the reactant during thermal decomposition of a solid. They comment on the superficiality of most of the work discussed. The application of an electric field is contrasted with the effect of selected additives as a means of obtaining information on the mechanism of a decomposition reaction. Both may alter the concentration of free electrons in the solid, but the effect of the field is more apparent in the vicinity of the surface. An example of an investigation of the effect of an electric field on a reaction is to be found in the work of the Panafieu et al. [373] on KN3. 

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Apart from purely field decrease in the height of the barriers using application of electric field with value E > kT/ql, where q is the electron charge, the change in electric conductivity of barrier-disarranged system can be caused by IC restructuring responsible for the current [150]. In this case one can deduce for VAC [150, 146, 159]... 

Pattanayak, J., Mandich, N.V., Mondal, K., Wiltowski, T., and Lalvani, S.B., Removal of iron and nickel from solutions by applications of electric field, Environ. Technol., 20, 317, 1999. 

When the gel is placed so as to be separated from the electrodes, the pH of the solution affects the degree of deformation. In alkali and acid regions, both PAANa and PAA gels swell at the anode side on application of electric fields. 

Figure 8.12 Longitudinal sheets with antiparallel polar symmetry are illustrated for achiral SmCA and SmC phases. Since it is not possible to switch to ferroelectric state in such system upon application of electric field, these structure should not be considered antiferroelectric.

Figure 8.13 Hypothetical smectic mesogen with hinge in center of core is illustrated. Such material could in principal switch to ferroelectric state, which we term the SmAPp, upon application of electric field in plane of layers. If this state exists in well on configurational hypersurface, then ground-state structure is antiferroelectric, denoted SmAPA.

The highly complex and unusual textures observed for B7 materials is complemented by unusual X-ray diffraction behavior. While the beautiful mystery of the B7 texture is not understood in detail, MHOBOW shows EO behavior, which allows some definitive statements regarding its nature. Thus, while some B7 materials are reported to be EO-inactive (no EO switching),54 and some are reported to exhibit antiferroelectric EO behavior,59 MHOBOW exhibits a unique texture change upon application of electric fields. 

Kabanov, A. A. etal., Russ. Chem. Rev., 1975, 44, 538-551 Application of electric fields to various explosive heavy metal derivatives (silver oxalate, barium, copper, lead, silver or thallium azides, or silver acetylide) accelerates the rate of thermal decomposition. Possible mechanisms are discussed. 

Fig. 26a and b. Influence of the electric field frequency on the electro-optical behaviour of the nematic polymer XII and scheme of mesogenic groups orientation before (A) and after (B) the application of electric field (a) optical transmission as a function of time at different frequencies (U = 30 V T = 75 °C) (b) optical transmission as a function of time upon application of an electric field at U = 85 V (f = 50 Hz) (1) relaxation upon switching the electric field off (2), upon application of an electric field (U = 80 V) of different frequency f = I (3) 5 (4) 7 (5) and 20 kHz (6) during the relaxation process... 

All the above-described effects show the high potential of the application of electric fields to block copolymer systems and also encourage the design of additional experiments aiming to find novel effects that might broaden the range of potential applications for block copolymer-based systems. 

Application of Electric Field Pulse Techniques 96 Supplementary Reading 97... 

Figure 9.13 (a) Initial scattering amplitude /, as functions of the scattering angle 0 determined from single spatial intensity distributions (Figure 9.7) after application of electric fields, a E0 = 0 kV/cm, b —1.5 kV/cm, and c —4 kV/cm. The intensity is normalized to the pump beam intensity Ip. (b) Initial scattering amplitude /, as functions of the externally applied electric field Ea for 0 = 50° and 15°, respectively, and normalized to the intensity without external field I o=0-... 

Transfection efficacy of naked DNA can be increased by physical methods such as electroporation and sonication. Electroporation employs electric pulses to punch holes in the cell membrane, usually smaller than 10 nm but larger than oligonucleotides. With the use of electroporation, DNA was delivered into the cytosol of cells by diffusion. Since its introduction in 1982, in vivo transfection has been achieved in skeletal muscle, fiver, skin, tumors, testis, and the kidney. Tsujie et al. (2001) developed a method to target glomeruli using electroporation in vivo wherein injection of plasmid DNA via the renal artery was followed by application of electric fields. The kidney was electroporated by sandwiching the organ... 

Application of a potential between reservoirs 1 (sample) and 4 (injection waste) electrokinetically pumps sample solution as indicated in Fig. 3. In this way, a geometrically defined 150 pm (90 pi) section of the separation channel can be filled [19]. If the injection potential is applied long enough to ensure that even the slowest sample component has completely filled the injection volume, a representative aliquot of sample can be analyzed (so-called volume defined injection). This is in contrast to electrokinetic sample injection in conventional capillaries, which is known to bias the sample according to the respective ionic mobilities [61]. These characteristic differences are shown schematically in Fig. 4. It should be noted that this picoliter sample injector is exclusively controlled by the application of electric fields and does not require any active elements with moving parts such as valves and external pumps. The reproducibility of the peak height of the injected sample plugs has been reported to be within 2 % RSD (relative standard deviation) and less [19,23]. 

Figure 8.8. (a) Reversible (R) and irreversible (I) poration of the cell membrane. (b) Charge polarization on the membrane due to the application of electric field. 

In this chapter the focus will be on the application of electrical fields in microreactors, and the potential of such systems for chemical synthesis will be outlined. The end of the chapter will give an overview of less-studied concepts, like electronic control of surface chemistry, and will discuss the opportunities offered by nanotechnology for achieving such control. 

Lately, some reports appeared about a new potential measurement technique with application of electric field scattering (frequency 1 MHz) [84,85]. This method is very interesting, for the possibility of the measurements in the condensed suspensions. It will allow to determine the stability of the suspension and developed investigations of the edl structure. To obtain precise values of the potential by this method, the knowledge of particle size distribution of the suspension is necessary. Previously used electrophoretic techniques, enabled the measurements to be taken only in the dilute solutions, which do not characterize the systems properly. 

Figure 3. Interface with pulsed field droplet deposition. Principle of the electrically mediated liquid deposition (lower panel). Deposition of the eluents from 4 parallel LC separations (upper panel. A). Samples cociystallized with matrix on hydrophilic islands with 400 pm diameter (upper panel, B) and droplets just before application of electrical field (upper panel, C). Reprinted with permission from Ericson et al. 2003. Copyright 2003 American Chemical Society.

The Stark effect requires the application of electric fields of the order of 10 Vcm or higher. The electrochemical interface, where molecules and ions are subjected to fields in the order of 10 Vcm S seems to be the ideal place to study this phenomenon. 

Aikawa et al. considered the effect of electric field on the phase transition in solutions of rigid-chain polymers for a PBLG solution in dioxane. Theoretical calculations have shown that the application of an electric field must shift the values of v towards lower concentrations. This conclusion was confirmed in experiments. According to the results obtained by Patel et al the application of electric fields also causes a shift in the temperature of the liquid crystalline transitions. 

Most of hydrodynamic methods have focused on increasing the particle back transport from the membrane-liquid interface by increasing the shear rate and the flow instability in the boundary layer. These techniques include secondary flows, spacers and inserts, pulsed flow, high shear rate devices, vibrations, and two-phase flow. The physical methods that are currently been tested to enhance filtration performance of membranes include the application of electric fields and ultrasound. 

As mentioned above, the application of electrical fields deforms the spherical form of the droplets to an ellipsoid thus decreasing the distance between two droplets. This deformation can also disturb the thin film between droplet surfaces and lead to coalescence, especially when using a.c. fields where an oscillating movement of the droplets also is induced. 

Akay, G. Dogru, M. Calkan, B. Calkan, O.F. Flow induced phase inversion phenomenon in process intensification and micro-reactor technology. Process intensification in water-in-crude oil emulsion separation by simultaneous application of electric field and polymeric demulsifiers. In Microreact Technology and Process Intensification Wang, Y., Halladay, J., Eds. Oxford University Press Oxford, 2005 Chapter, 18. 

Fiber orientation can be induced by simultaneous shearing and application of electric fields. Such conditions were simulated in a plate rheometer in which the plates were also inducing an electric field. Dielectric particles of filler were oriented in the same direction as that of the electric field. The time to reach an equili-... 

M. Mizoguchi and N. Ohta. Fluorescence of an electron donor-acceptor system in a polymer film under the simultaneous application of electric field and magnetic field. Chem. Phys. Lett., 372(l-2) 66-72, 2003. 

An even more useful functionality of this configuration is active modulation of the relative positions of droplets [56]. Because an electric field can be applied to chip-integrated electrodes, GERF can solidify between them and the flow in the relevant channel will be frozen, as shown in Fig. 8e, f. The relative droplet position can be adjusted in this way. Moreover, as the influence is achieved through medium fluid (GERF), direct application of electric field to target droplets is... 

Dialysis (5) as a unit operation considerably antedates gas and liquid permeation. Membrane dialysis was used by Graham in 1861 to separate colloids from crystalloids. The first large industrial dialyzers, for the recovery of caustic from rayon steep liquor, were installed in the United States in the 1930s. Industrial dialysis units for recovery of spent acid from metallurgical liquors have been widely used since 1958. In dialysis, bulk flow of solvent is prevented by balancing the osmotic pressure, and low-molecular-weight solutes are recovered by preferential diffusion across thin membranes having pores of the order of 10 cm. Frequently diffusion is enhanced by application of electric fields. 

The effects of the electric field, E, have been determined, by ah initio calculations, by evaluating the saving in the standard enthalpy of formation (AHf) of different ion-pairs M+X on application of electric fields (regarded as dipolar, uniform, and continuous) of different types [46]. Calculations were based on the effect of the electric field E (with optimum effects when considering E to be collin-ear with the dipole moment) according to ion-pair dissociation by considering the stabilization (decreases in AHf) as a function of the interatomic distance, d, between Li+ and F and the nature of ions at their equilibrium distance for several... 

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