Polar Dielectric Liquids Research Articles

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

The preparation of electrohydrodynamic bridges from polar dielectric liquids.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Clusters Formation in Salts Solution in Polar Dielectric Liquids and Electrically-induced Separation of Solvated Ions

The aim of study is to demonstrate that separation of solvated ions in solution of mix of salts under the action of external periodic electric field happens because of around ions there are formed clusters consisting of molecules of solvent and the sizes of such clusters have dimensions ~ 0.1 μm. In investigations the sizes of clusters theoretically were defined and experimentally value of frequency of external electric field which action excites the effect of separation of the solvated ions was defined. Experiments were done in the Technical Physics Chair of the National Research Tomsk Polytechnic University. At theoretical determination of the dimensions of clusters Poisson's equation was solved and was considered that polar molecules of solvent are oriented under the action of electric field of an ion. The chemical composition of samples of solutions was determined by means of the X-ray excited fluorescent radiation analysis method. Theoretical estimates and results of experiments confirmed the assumption that clusters which are formed around ions in solutions have the dimensions ~ 0.1 μm. Results of investigation testify that placing of volume distributed electric charge of ion in Original Research Article British Journal of Applied Science & Technology, 4(18): 2014 2539 dielectric liquid is accompanied by formation of the supramolecular particles, which we called “clusters”, linear sizes of which is significantly more than first and second radiuses of solvation (~ 1 Angstrom) and reach size ~ 0.1 μm. At such sizes inertial properties of clusters and their natural frequencies give the chance to operate their movement by means of action of external electric field on solution.

Formation of associates of solvated cations in salt solutions in polar dielectric liquids

Experimental results are presented on excitation of oscillations of polarization charges of solvated ions in an aqueous solution of a mixture of cerium and lead nitrates under an external asymmetric electric field and the directed motion of solvated cerium and lead cations, caused by this process. The applicability of the approximation of the existence of a self-consistent electric field in the solution volume to explain the observed frequency ranges of the manifestation of the effect of electroinduced selective drift of solvated cations is demonstrated. The results of a theoretical analysis of the possibility of forming associates from solvated ions are presented.

The effect of four torques on dielectric behavior

In his notable book 'Polar Molecules' published in 1929, Debye showed that for polar dielectric liquids, dispersion and absorption could be described by the operation of a relaxation mechanism characterized by a frequency-dependent complex permittivity. On the basis of certain assumptions, he developed an expression for that dependence. Among those assumptions was that the polar molecules were taken to have no inertia, and in consequence they can not have any net torque acting on any of them at any time. The polar molecules were taken to be present in a very dilute solution of a polar liquid in a non-polar solvent. Therefore dipole-dipole interactions were ignored, and the driving torque on any dipole was taken to be caused by the applied field alone. That torque was taken to be counterbalanced at all times by a frictional torque proportional to the instantaneous angular velocity of each particular polar molecule. This retarding torque arises from an inner friction, and is not the same as, but is in some way related to, the macroscopic viscosity of the liquid. However, the action of the frictional torque in cancelling the applied torque does not account for energy storage in the liquid. Debye establishes the necessary phase relationships by the postulate that the dipole moment of the polar molecules is complex. While this postulate is quite permissible, it does not give an insight into the physical mechanism involved. In addition to the two torques taken into account by Debye, in a paper published in 2005 Calderwood proposed that there is a third torque acting on the dipoles which is responsible for the electrostatic energy stored when a specimen of a polar dielectric liquid is charged, and which is released on specimen discharge. A detailed account of the behavior of this torque and its significance is given in that paper. One of the features of the third torque is that, in contrast to the friction torque which is dissipative, it is conservative. That is to say, it is spring-like in nature. It is that characteristic which enables the specimen to store and release energy. The presence of spring-like elements in any mechanical or electrical system can also significantly modify its behavior. In this paper a criterion is derived which indicates whether or not significant features of dielectric behavior might be attributed to the third torque. The treatment of Debye did not take the inertial effect of the polar molecules into account. However, these molecules do possess some inertia and so a fourth torque is necessarily associated with any acceleration to which they may be subjected. Account is taken of this in the present analysis by the introduction of the fourth torque. This treatment, like that of Debye, does not take account of dipole-dipole interaction. It is therefore only applicable to dilute solutions of polar molecules in a non-polar solvent.

The Mechanism of Electroviscosity. I. Electrohydrodynamic Effect on Polar Liquids

An electrohydrodynamic explanation of the electroviscous effect in relation with the conduction process in polar dielectric liquids is presented. The authors observed the instability of flow, the transition from the laminar convective motion to the turbulence in d.c.field and different stages of the conduction process (injection and bulk-conduction) according to the frequency in a.c.field.