Liquid dielectric

About: Liquid dielectric is a research topic. Over the lifetime, 3702 publications have been published within this topic receiving 45150 citations.

An electrokinetic model of drop deformation in an electric field

Abstract: An electrokinetic model is proposed to describe a slight drop deformation which is induced by a weak external electric field The fluids forming the system are considered Newtonian incompressible dielectric liquids containing free electric charge carriers According to the model, the charge carriers take part in migration, diffusion and convection transport and there is no solute adsorption at the interface Thermodynamic quasi-equilibrium at the interface is assumed for the charge carriers in the contacting liquids The interfacial thermodynamic equilibrium is described using a common distribution coefficient for all the carriers The problem is simplified by assuming equal diffusion coefficients for the different charge carriers within the same liquid An analytical expression is obtained for slight drop deformation which is proportional to the second power of the applied field strength magnitude The expression derived represents the drop deformation as a function of the parameters employed in previous theories (O’Konski & Thacher 1953; Allan & Mason 1962; Taylor 1966) as well as two additional parameters The additional parameters are the ratios of the drop radius to the Debye lengths of the outer and inner liquids, respectively The expression obtained for the drop deformation is valid for arbitrary values of these parameters According to the theory prediction, with an increase in the drop radius, the drop deformation monotonically changes from that obtained by O’Konski & Thacher (1953) and Allan & Mason (1962) for perfect dielectric liquids to that obtained by Taylor (1966) for leaky dielectric liquids Two simplified versions of the general expression are suggested to describe particular cases of a conducting drop in a perfect dielectric liquid and of a perfect dielectric drop in a conducting liquid

Electric-field effects on nematic droplets with negative dielectric anisotropy

Abstract: Using polarization microscopy, we have investigated the director configurations of droplets of a nematic liquid crystal with negative dielectric anisotropy and perpendicular boundary conditions subjected to electric fields. The droplets were suspended in liquid poly(dimethyl siloxane) and electric fields were applied both parallel and perpendicular to the viewing direction. The resulting director pattern is deduced by comparing the experimental transmission patterns with patterns calculated from various director models. For low fields, we observe a director field which is essentially radial, but with some azimuthal twist superimposed and a radial point (hedgehog) defect at the center. At intermediate fields, the hedgehog defect moves away from the center along the electric-field direction, while at the highest fields a line defect appears which lies along the diameter parallel to the field. Comparison of the transmission patterns with model calculations yields good agreement for the low- and intermediate-field cases, and reasonable agreement for the high-field case.

Electrohydrodynamic instability of the interface between two fluids confined in a channel

Abstract: The stability of the interface between two dielectric fluids confined between parallel plates subjected to a normal electric field in the zero Reynolds number limit is studied analytically using linear and weakly nonlinear analyses, and numerically using a thin-layer approximation for long waves and the boundary element technique for waves with wavelength comparable to the fluid thickness. Both the perfect dielectric and leaky dielectric models are studied. The perfect dielectric model is applicable for nonconducting fluids, whereas the leaky dielectric fluid model is applicable to fluids where the time scale for charge relaxation, $\epsilon \epsilon_o/\sigma$, is small compared to the fluid time scale $(\mu R/\Gamma)$, where $\epsilon_o$ is the dielectric permittivity of the free space,\epsilon and \sigma are the dielectric constant and the conductivity of the fluid,\mu and \Gamma are the fluid viscosity and surface tension, and R is the characteristic length scale. The linear stability analysis shows that the interface becomes unstable when the applied potential exceeds a critical value, and the critical potential depends on the ratio of dielectric constants, electrical conductivities, thicknesses of the two fluids, and surface tension. The critical potential is found to be lower for leaky dielectrics than for perfect dielectrics. The weakly nonlinear analysis shows that the bifurcation is supercritical in a small range of ratio of dielectric constants when the wavelength is comparable to the film thickness, and subcritical for all other values of dielectric constant ratio in the long-wave limit. The thin-film and boundary integral calculations are in agreement with the weakly nonlinear analysis, and the boundary integral calculation indicates the presence of a secondary subcritical bifurcation at a potential slightly larger than the critical potential when the instability is supercritical. When a mean shear flow is applied to the fluids, the critical potential for the instability increases, and the flow tends to alter the nature of the bifurcation from subcritical to supercritical.