Orientation of liquid crystalline 5CB under an external electric field

The orientation characteristics of pre-aligned liquid crystalline 5CB (4-n-pentyl-4′-cyanobiphenyl) in a germanium cell with unidirectional rubbed polyimide-coated surfaces have been investigated. Orientation of 5CB molecules near the polyimide surface and those representing average properties of the system (i.e., the bulk) are compared. The orientation of the bulk is monitored by transmission Fourier transform infrared (FT-IR) spectroscopy while that of the molecules next to the surface is observed via attenuated total reflection (ATR) FT-IR spectroscopy. There are significant differences in orientation characteristics between the two groups of molecules. For molecules near the polyimide surface, there is an observable difference in orientation of the soft and hard segments of the liquid crystalline. Moreover, they show depth dependent orientation.     

Desorption of hydrogen from the electrode surface under influence of an external magnetic field

The effect of a uniform magnetic field in perpendicular-to-electrode configuration, on the hydrogen evolution reaction was investigated during the deposition of Fe and CoFe alloys. It was found that the desorption of hydrogen is supported in a magnetic field. This effect is discussed in details with respect to the micro-magnetohydrodynamic convection, which arises due to the fluctuation of the current distribution close to the H₂ bubble.     

Simulations of a weakly conducting droplet under the influence of an alternating electric field

We investigate the electrohydrodynamics of an initially spherical droplet under the influence of an external alternating electric field by conducting axisymmetric numerical simulations using a charge-conservative volume-of-fluid based finite volume flow solver. The mean amplitude of shape oscillations of a droplet subjected to an alternating electric field for leaky dielectric fluids is similar to the steady-state deformation under an equivalent root mean squared direct electric field for all possible electrical conductivity ratio and permittivity ratio of the droplet to the surrounding fluid. In contrast, our simulations for weakly conducting media show that this equivalence between alternating and direct electric fields does not hold for . Moreover, for a range of parameters, the deformation obtained using the alternating and direct electric fields is qualitatively different, that is, for low and high , the droplet becomes prolate under alternating electric field but deforms to an oblate shape in the case of the equivalent direct electric field. A parametric study is conducted by varying the time period of the applied alternating electric field, the permittivity and the electrical conductivity ratios. It is observed that while increasing has a negligible effect on the deformation dynamics of the droplet for , it enhances the deformation of the droplet when for both alternating and direct electric fields. We believe that our results may be of immense consequence in explaining the morphological evolution of droplets in a plethora of scenarios ranging from nature to biology.     

Three-dimensional square water in the presence of an external electric field

In this work we study a tridimensional statistical model for the hydrogen-bond (HB) network formed in liquid water in the presence of an external electric field. This model is analogous to the so-called square water, whose ground state gives a good estimate for the residual entropy of the ice. In our case, each water molecule occupies one site of a cubic lattice, and no hole is allowed. The hydrogen atoms of water molecules are disposed at the lines connecting nearest-neighbor sites, in a way that each water can be found in 15 different states. We say that there is a hydrogen bond between two neighboring molecules when only one hydrogen is in the line connecting both molecules. Through Monte Carlo simulations with Metropolis and entropic sampling algorithms, and by exact calculations for small lattices, we determined the dependence of the number of molecules aligned to the field and the number of hydrogen bonds per molecule as a function of temperature and the intensity of the external field. The results for both approaches showed that, different of the two-dimensional case, there is no maximum in the number of HBs as a function of the electric field. However, we observed nonmonotonic behaviors as a function of the temperature of the quantities of interest. We also found the dependence of the entropy on the external electric field at very low temperatures. In this case, the entropy vanishes for the value of the external field for which the contributions to the total energy coming from the HBs and the field become the same.     

Calculation of the Helmholtz potential of an elastic strand in an external electric field

We derive from statistical mechanics the Gibbs free energy of an elastic random-walk chain affected by the presence of an external electric field. Intrachain charge interactions are ignored. In addition, we find two approximations of the Helmholtz potential for this system analogous to the gaussian and Cohen-Pade? approximations for an elastic strand without the presence of an electric field. Our expressions agree well with exact numerical calculations of the potential in a wide range of conditions. Our analog of the gaussian approximation exhibits distortion of the monomer density due to the presence of the electric field, and our analog of the Cohen-Pade? approximation additionally includes finite chain extensibility effects. The Helmholtz potential may be used in modeling the dynamics of electrophoresis experiments.     

Response properties of AgCl and AgBr under an external static electric field: A density functional study

Density functional theory has been applied to investigate the effect of electric field on the electronic properties of AgCl and AgBr crystals using a static electric field perturbation. A reduction in the band gap value and widening of the band widths are observed with increase in the macroscopic field value indicating a considerable red shift in the absorption spectrum of AgCl and AgBr in the presence of an external electric field. Further, dielectric properties and lattice vibrations at the gamma point are calculated with three different functionals using the CPKS and the Berry phase approach as implemented in CRYSTAL09 code. Finally, the breakdown strength of AgCl and AgBr crystal is evaluated using Callen’s equation. In contrast to the case of alkali halides, it is found that the inclusion of the numerically calculated effective mass ratio into the Callen’s equation considerably improves the agreement between the calculated dielectric strength and the available experimental datum.     

Desorption of hydrogen from an electrode surface under influence of an external magnetic field – In-situ microscopic observations

The effect of a magnetic field in the perpendicular-to-electrode configuration on the hydrogen evolution reaction (HER) was investigated during the deposition of Co. An enhanced desorption of hydrogen in the form of numerous small bubbles was found by combining potentiostatic investigations, coupled with an electrochemical quartz crystal microbalance (EQCM), and simultaneous microscopic observations of the electrode surface. The results are consistent with the recently proposed qualitative model [J.A. Koza, M. Uhlemann, A. Gebert, L. Schultz, Electrochem. Commun. 10 (2008) 1330].     

Reproducibility in the unfolding process of protein induced by an external electric field

The dynamics of proteins are crucial for their function. However, commonly used techniques for studying protein structures are limited in monitoring time-resolved dynamics at high resolution. Combining electric fields with existing techniques to study gas-phase proteins, such as single particle imaging using free-electron lasers and gas-phase small angle X-ray scattering, has the potential to open up a new era in time-resolved studies of gas-phase protein dynamics. Using molecular dynamics simulations, we identify well-defined unfolding pathways of a protein, induced by experimentally achievable external electric fields. Our simulations show that strong electric fields in conjunction with short-pulsed X-ray sources such as free-electron lasers can be a new path for imaging dynamics of gas-phase proteins at high spatial and temporal resolution.

Controlled unfolding of proteins can reveal structural properties and give insights of the proteins'' dynamics. We show the feasibility of unfolding proteins in the gas phase using electric fields, with a well-defined path at high field strengths.     

Transient effects in electrolytic cells submitted to an external electric field

We analyse transient effects in an electrolytic cell submitted to an external voltage and determine the relaxation time of the redistribution of the ions and of the potential. We consider the case in which adsorption effects at the interface with the electrodes are present and show that the typical relaxation time, for applied voltage V ₀25 mV, is of the order of tens of seconds for commercial nematic liquid crystals. When V ₀>25 mV the linearized analysis is no longer valid. In this case, the relaxation time depends on the applied voltage. Increasing V ₀, but still remaining in the low amplitude limit, the relaxation time starts increasing. This indicates that the reduction of the actual field in the sample, for moderate values of V ₀, plays an important role. For large values of V ₀, the relaxation time is a decreasing function of V ₀. This result is interpreted in terms of a simple model, according to which the ionic charge is localized in a surface layer whose thickness depends on the amplitude of the applied voltage.     

Nuclear magnetic relaxation of ionic nuclei moving in an external electric field

We have experimentally investigated nuclear magnetic relaxation of some quadrupolar ionic nuclei (²³Na⁺, ⁸⁷Rb⁺ and ³⁵Cl⁻ ) in electrolyte solutions in non-equilibrium states. The measurements of relaxation rates 1/T₁ in the presence of a direct electric field, and thus also an electric current, revealed that differences can occur in comparison with relaxation in the absence of the field. In some systems no change in the relaxation rate was observed, but in certain other (non-aqueous) systems there was a change in the quadrupolar relaxation rate in the presence of the field.     

A molecular orbital study of the effect of an external electric field on methanol

We report the results of INDO-MO calculations to investigate the influence of an external electric field on methanol. We predict that during a field-ionisation experiment, ionisation will occur from a quite different molecular geometry than the field-free olie.     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.     

The influence of an electric and magnetic field in chemical reactions

We have shown that a simultaneous application of uniform and constant electric and magnetic fields cannot affect the equality of the equilibrium enantiomeric populations in a racemic reaction mixture. Hence, whatever the sources of the rotations reported, they cannot have had their origin in uniform applied fields if the reactions have gone to completion.     

Control of effect on the nucleation rate for hen egg white lysozyme crystals under application of an external ac electric field

The effect of an external ac electric field on the nucleation rate of hen egg white lysozyme crystals increased with an increase in the concentration of the precipitant used, which enabled the design of an electric double layer (EDL) formed at the inner surface of the drop in the oil. This is attributed to the thickness of the EDL controlled by the ionic strength of the precipitant used. Control of the EDL formed at the interface between the two phases is important to establishing this novel technique for the crystallization of proteins under the application of an external ac electric field.     

基于密度泛函理论的外电场下c-C4F8的结构及其特性

采用密度泛函理论CAM-B3LYP/DGDZVP2对c-C4F8进行优化计算,得到基态分子结构.在该结构基础上施加线性外电场(0~10.284 V·pm^-1),获得了c-C4F8的几何特性、能量、前线轨道能级、键能和红外光谱数据.结果表明:当电场沿x轴变大时,c-C4F8的点群从D2d变为C1,偶极矩和极化率不断增大,结构稳定性降低;分子总能量和能隙不断减小,且C(4)-F(10)键的键能降低速度最快,最有可能率先在外电场作用下断裂,导致c-C4F8结构和对称性被破坏.同时c-C4F8的绝热电子亲和能单调上升,分子吸收自由电子的能力增强;红外光谱中,吸收峰的个数增加,4个主要吸收峰发生了红移.     

Local order and shape of a polymer chain in an external electric field

A solution of polymer chains in the presence of an external electric field is considered. Dipole-like interactions between polymer chain segment-vectors and the electric field are assumed to be proportional to the cosine of the angle between the segment-vector and the direction of the electric field. Parameters characterizing the shape of the chain (i.e., the chain end-to-end distance and cross-section per chain), and parameters describing the local order at the segmental and chain level (i.e., moments of the first and second Legendre polynomials 〈P₁〉 and 〈P₂〉 are calculated. The optical anisotropy and the molecular shape change induced by the external electric field are discussed.     

Thermal desorption of cations from polysilicates and zeolites in an external electric field

The desorption of cations from crystalline polysilicates and polysilicic acids, A and Y zeolites, and natural mordenite in the NH₄, H, and dealuminized forms under the action of a strong electrostatic field at temperatures ranging from 20 to 600°C has been studied. The desorption of sodium and potassium cations was detected above a temperature of 150–200°C, and magnesium, calcium, and aluminum cations were not detected. Potassium cations are desorbed at lower temperatures than are sodium cations. Zeolite NaA retains cations more strongly than-does zeolite NaY. The observed spectra are consistent with the concentrations of the cations and the structural features of the samples studied.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 626–629, September–October, 1988.