Water vs. ethanol zinc-based nanoparticles synthesized via laser ablation under various uniform electric fields and aging effects

The electrohydrodynamic flow associated with a fluid drop in an electric field is a consequence of the tangential electric stress at the fluid interface. The tangential viscous stress due to the electrohydrodynamic flow arises to just balance the tangential electric stress at the fluid interface so that the traction boundary condition is satisfied. Influenced by both the local electric stress and viscous stress, the drop interface may exhibit various shapes. The presence of fluid flow also leads to charge convection phenomena. The relative significance of the charge convection effect is usually measured in terms of the electric Reynolds number, Re E , defined as the ratio of the timescales of charge convection by flow and that for charge relaxation by ohmic conduction. This work presents a quantitative analysis of the charge convection effects in a framework of the leaky dielectric model at finite Re E , which has not been considered in previous investigations. Axisymmetric steady flows driven by an applied uniform electric field about a deformable fluid drop suspended in an immiscible fluid are studied by computational means of the Galerkin finite–element method with supplementary asymptotic analysis. The results of finite–element computations are in general agreement with the prediction by the asymptotic analysis for spherical drops at vanishingly small Re E . A common effect of charge convection is found to reduce the intensity of electrohydrodynamic flow. As a consequence, oblate drops are predicted to be less deformed in an electric field when charge convection is taken into account. The prolate drops are often associated with an equator–to–pole flow, which convects charges toward the poles to form a charge distribution resembling that in a highly conducting drop immersed in an insulating medium. Therefore, charge convection tends to enhance the prolate drop deformation. In many cases, charge convection effects are found to be significant even at apparently small Re E , corresponding to the charge relaxation time–scale about 10 −3 s, suggesting that many experimental results reported in the previous publications could have been influenced by charge convection effects.

The purpose of this study is to elucidate flame propagation behavior under the application of uniform and non-uniform electric fields by using a constant volume vessel. Two electrodes are attached to the ceiling and the bottom of the combustion chamber and electric fields are applied in the direction of the chamber's vertical axis. A Nd:YAG laser is used to apply laser-induced breakdown for igniting the mixture at the center of the combustion chamber. A homogeneous propane-air mixture is supplied at three equivalence ratios of 0.7, 1.0 and 1.5 and ignited under atmospheric pressure and room temperature. Under a uniform electric field, the premixed flame rapidly propagates both upward and downward, forming a cylindrically shaped flame front. The maximum combustion pressure decreases with increasing input voltage because the flame front reaches the chamber wall rapidly and the heat loss to electrodes increases. However, the combustion duration is little affected by the input voltage. In a non-uniform electric field, the flame propagation velocity in the downward direction increases. Combustion is markedly enhanced when the input voltage is larger than 12 kV because a brush corona discharge occurs and intense turbulence is generated at the flame front. For both uniform and non-uniform electric fields, the horizontal flame velocity is almost the same.

Electric field plays a key role in producing required nanofibers in electrospinning. This study aims to achieve uniform electric field distribution in multijet electrospinning by designing the appropriate spinneret and collector geometry. Based on the three-dimensional electric field simulation, three kinds of spinneret and two kinds of collectors have been designed. The simulation results show that a flat spinneret creates a more uniform electric field distribution than the multineedle spinneret with an auxiliary plate. The two-step spinneret can intensify the electric field at the central area and create a rather uniform electric field. A smaller collector creates a more uniform electric field distribution, and a curved collector creates a more uniform surface electric field. The simulation results have been verified by experiments. The experiments show that thinner and more uniform fibers are collected when using the two-step spinneret and a smaller flat collector, and the thickness of fiber mat is mor...

The interband multi-photon absorption spectrum from a semiconductor superlattice induced by an intense optical wave in the presence of uniform magnetic and electric fields is analysed theoretically. The oscillating electric field of the optical wave and the uniform electric and magnetic fields are all directed perpendicular to the heteroplanes. The explicit dependences of the coefficient of the multi-photon absorption on the frequency and magnitude of the oscillating electric field, on the superlattice parameters and on the magnitudes of the uniform electric and magnetic fields are obtained. The uniform electric field is assumed to be sufficiently strong to provide Wannier - Stark localization of the carriers. The electron - hole cyclotron frequency and the frequency of the Stark oscillations are taken to be commensurate with their ratio being rational. It is shown that, under these conditions and in contrast to one-photon spectra, an enhancement of the series of resonances could arise. It is also shown that the form of the spectrum depends on the relationship between the cyclotron and Stark frequencies and on the number of photons involved.

To investigate the dielectrophoretic motions of multiple particles, we have performed the so-called direct numerical simulations on two-dimensional flows involving inertialess dielectric particles of two to five suspended in a viscous fluid under a uniform external electric field and then compared the results with those of the corresponding magnetophoretic counterparts. For the simulations, the electric field (or the force acting on each particle) is described by the numerical solution of the Maxwell equation (or Gauss’s law), where the smoothed representation technique is employed to tackle the jump of electric conductivity across the particle-fluid interface. The flow field, on the other hand, is described by the solution of the continuity and momentum equations, where one-stage smoothed profile method is employed to satisfy the no-slip condition at the interface. In all the simulations, the particles are initially equi-spaced on a circle with an origin at the center while a uniform electric field is externally imposed. Results show that all particles move with repelling or attracting one another depending on the locally nonuniform electric field formed due to the presence of multiple particles. Consequently, they become clustered largely into two groups, then revolve in the clockwise or counterclockwise direction, and finally get aligned in a line with the field direction. One exception is their initial configuration which is symmetric with respect to the axis perpendicular to the electric-field direction, where all the particles move eternally far away from one another with keeping the symmetry. In addition, it is found that the two-dimensional relative motions of dielectric particles under a uniform external electric field are qualitatively in fairly exact agreement with those of paramagnetic particles suspended in a nonmagnetic fluid under a uniform external magnetic field.

Applying the atomic characteristic boundary model, the boundary contours of inert atoms were evaluated in uniform strength electric field, whose strength was 5.292×10-5-5.292×10-3 a.u.. The calculated results by an ab initio method showed that the boundary of an atom in a uniform electric field was close to elliptical, and the variation of atomic boundary contour was increased with the increase of the electric field strength. In the same electric field, the larger the atomic number was, the bigger the variation of atomic boundary contour was. Further, it was shown that the mean variation rates of the atomic radial sizes of these atoms in the electric field of unit strength had a good linear relationship with the experimental values of atomic polarizability.

Interband optical transitions in a semiconductor superlattice induced by an intense optical wave in the presence of uniform electric and magnetic fields are analysed. Both the oscillating electric field of the optical wave and the uniform magnetic field are directed perpendicular to the heterolayers whilst the uniform electric field is in a direction parallel to the heterolayers. The superlattice potential is modelled by a periodic chain of delta -function-type barriers. Quasi-energetic time-dependent states are used. The explicit dependence of the coefficient of the multiphoton absorption on the frequency and magnitude of the light wave, the superlattice parameters and the magnitudes of the uniform fields is obtained. It is shown that the dynamical Stark effect induced by the strong oscillating electric field leads to a shift of the edge of absorption to shorter wavelengths. The form of magneto-absorption essentially depends upon the parity of the number of absorbed photons and the relationship between the separation of the Landau levels and the total width of the electron and hole minibands. It is found that the main effect of a uniform electric field is to shift the absorption edge to longer wavelengths (the Franz-Keldysh effect).

Continuum theory for ionic field charging of spheroidal aerosols in nonuniform electric field

Characterization techniques for a MEMS electric-field sensor in vacuum

Droplet deformation and mechanical behavior under external electric field are fundamental in electrohydrodynamic research. Based on the volume-of-fluid (VOF) method and adding electric force to Navier-Stokes equations as an additional source term, a simulation method considering fluid flow and electric field in two-way coupling is proposed. Using this method, the deformation/motion of leaky dielectric droplet and charged droplet under external uniform and non-uniform electric field is investigated respectively. The shape deformation coefficient calculated by the proposed method is close to the theory value of leaky dielectric droplet under uniform electric field in small deformation condition; thus the validity of the numerical method proposed in this study is verified. The results show that the charge redistribution modes of leaky dielectric droplet depend on the property difference between droplet and the around fluid, and the droplet may deform into either prolate or oblate shapes. The electric field strength only affects the droplet shape deformation coefficient. The external uniform electric field induces strong circulation motion inside the leaky dielectric droplet without moving the droplet. Because of the effect of Coulomb force, the charged droplet may deform into prolate and move along the electric field direction. However both leaky dielectric droplet and charged droplet may move along the electric field direction, resulting in different shapes simultaneously under the non-uniform electric field. The numerical method coupling fluid flow with electric field proposed in this paper could provide an effective approach to electrostatic spray, electrophoresis and other complex engineering electrohydrodynamic researches.

Enhanced evaporation and heat transfer of sessile droplets via coupling electric field and temperature field

This chapter is concerned with introducing a number of model problems, based on the relativistic motion of charged particles in static electric and magnetic field configurations. It discusses that these configurations include uniform dipole magnetic fields, uniform electric fields, quadrupole magnetic and electric fields, superpositions of uniform electric and magnetic fields, periodic magnetic dipole field or magnetic undulator. It explains that these model problems also allowed this chapter to introduce some rudimentary examples of analyses that are based on both relativistic and Hamiltonian formalisms. It adds that these analyses will help form the basis of more complex investigations of charged particle motion.

The changes in conformational structure of polyampholyte polypeptides adsorbed at the surface of a charged spherical gold nanoparticles polarized in a uniform external electric field have been studied by means of molecular dynamics. Distributions of the mean unidimensional density of the polypeptide atoms along the axis of the nanoparticle polarization and radial distributions of the mean density of the atoms of polypeptides adsorbed at the nanoparticle surface have been computed. When the surface charge of the charged nanoparticle in one of the near-pole regions are compensated by the charges induced at the nanoparticle by the external electric field, the polyampholyte skirt non-symmetric with respect to the equator has been formed. Compaction of the macromolecular layer at one of the near-pole regions has occurred, whereas the polyampholyte skirt at the other near-pole regions has been swollen with the formation of the macromolecule chain loops, their length depending on the spacing between the charged units in the macromolecule. When the total charge of the nanoparticle in the uniform electrical field is low, the polyampholyte skirt stretched along the polarization has been formed at the nanoparticle surface. At low strength of the external uniform electric field, the charged nanoparticle has been uniformly wrapped by a macromolecular skirt consisting of three layers: two oppositely charged ones and a neutral layer between them.

Using the closed orbit theory, we calculate the photodetachment cross section of H-ion in a uniform electric field near a metal surface. The results show that the photodetachment cross section of H- near the threshold has a significant change after the metal surface has been placed in the uniform electric field. Compared with the situation of the photodetachment of H- ion in a single uniform electric field, the oscillating amplitude of the photodetachment cross section of this system is increased and the oscillating frequency is decreased. If we keep the electric field strength at a given value, we find that with the increase of the distance between the metal surface and the H- ion, the oscillating amplitude of the photodetachment cross section decreases and the oscillating frequency increases. When the ion-to-surface distance increases to a certain value, the influence of the metal surface disappeared, and the photodetachment cross section approaches the photodetachment cross section of H- in a uniform electric field.

Numerical computations and order of magnitude estimates are presented for the periodic generation and coalescence of bubbles due to the injection of a constant flow rate of a gas through a circular orifice at the bottom wall of an inviscid dielectric or very polar liquid that is at rest and subject to a uniform vertical electric field far from the orifice. The problem depends on five dimensionless parameters: a Bond number based on the radius of the orifice; Weber and electric Bond numbers whose square roots are dimensionless measures of the flow rate of gas and the applied electric field; the dielectric constant of the liquid; and the contact angle of the liquid with the bottom wall. The bubbles that grow quasi-statically at the orifice for small values of the Weber number are always elongated vertically by the electric stress that acts on their surface when an electric field is applied. The volume of these bubbles at detachment may reach a maximum at a certain value of the electric Bond number, if the Bond number is sufficiently small, or decrease monotonically with the electric Bond number if the Bond number is larger. In both cases the bubbling ceases to be periodic beyond a certain value of the electric Bond number, apparently giving way to more complex bubbling regimes, which are not investigated here. Bubble interaction and eventually coalescence occur when the Weber number is increased keeping the electric Bond number in the range of periodic bubbling. Different periodic regimes are described. It is shown that a moderate electric field may increase the value of the Weber number above which coalescence occurs without changing the shape of the bubbles much. A large electric field may suppress coalescence but it also favours the development of upward and downward jets that cross the bubbles and may cause their breakdown.