Dielectric permittivity fluids

Dielectric films Dielectric fluids Dielectric insulators Dielectric masking Dielectric materials Dielectric permittivity Dielectrics... 

Guillot and Guissani [56] and Weiss and Schroer [221] went one step further. Guillot and Guissani considered the effect of unscreened DD interactions on the FL theory. They also performed an approximate treatment of unscreened DD interactions in the framework of the MSA. In contrast, Weiss and Schroer theory (WS) considers ionic screening of the DD interactions by the remainder of the fluid, the change of the dielectric permittivity caused by... 

The method used in determining the dense dielectric permittivity of a definite material consists in defining a fluid in which the material cannot dissolve and further to measure the effective permittivity of various particulate media/fluid mixtures corresponding to various porosity. The interception point of the curves representing the variation of the permittivity of the material with porosity (through the effective medium equation, see section 3.2) gives the dense state permittivity. 

Anisotropic fluids, of which nematic liquid crystals are the most representative and simplest example, are characterized by an anisotropic dielectric permittivity. The nematic phase has D,yuh symmetry, and in a laboratory frame with the Z axis parallel to the C , symmetry axis (the director) the permittivity tensor has the form ... 

Another class of systems for which the use of the continuum dielectric theory would be unable to capture an essential solvation mechanism are supercritical fluids. In these systems, an essential component of solvation is the local density enhancement [26,33,72], A change in the solute dipole on electronic excitation triggers a change in the extent of solvent clustering around the solute. The dynamics of the resulting density fluctuations is unlikely to be adequately modeled by using the dielectric permittivity as input in the case of dipolar supercritical fluids. 

A convincing but indirect proof indicating a close connection between the motions of hydrogen atoms and the dielectric properties of aqueous fluids follows from the comparison of the static dielectric permittivity ss of ice Ih and ice II. In the former, where the proton disorder is emphasized, ss 100, while in the latter, where such a disorder is lacking, ss = 3.66 [17]. 

Rather than an exhaustive comparison of different properties, the dependence of few key properties on the tetrahedral order of the hydration shell has revealed important features of the hydration [60]. In particular, the temperature of maximum density Tmd has been linked with the ability to show hydrophobic effects, the diffusion constant D sets the timescale with respect to the forces, and the dielectric permittivity e is a measure of the dielectric properties of the fluid. Comparing the series of water models, a linear regression of the calculated Tmd with gives... 

In (32.12), H/j, is a dimensionless parameter comparing the viscosity of the fluid used in an electrospray to other fluid parameters such as fluid surface tension, fluid density, dielectric permittivity of the fluid and also the dielectric permittivity of free space. When is much greater than 1 then viscous effects are negligible. 

The external static electric field applied to a dielectric material induces fire polarisation P, that is the dipole moment per unit volume. For low fields P is prt rtional to the electric field E [1>3], P = 8o(8s - 1) E, where 8s is the relative dielectric permittivity or dielectric constant and 8o is the dielectric permittivity of free space. All these quantities concom the macroscopic volume of the dielectric medium. In order to relate them to the relevant microscopic param ers (for example dipole moment and polarisability) the local electric field Eioc acting on a molecule must be known. The relation between Eioc and E is the crucial problem of the physics of dielectrics and has not been solved in general. For isotropic fluids the Onsager theory is commonly used [4]. 

Most rock-forming minerals have a permittivity in the order of =3—10 higher values show, for example, sulphides and some oxides. The dielectric permittivity of water is about 80. This results in a strong correlation between permittivity and the water content of a rock. Table 8.9 shows some more data for the permittivity of fluids. 

TABLE 8.9 Dielectric Permittivity of Some Pore Fluids, Including Contaminants... 

Sharma, M.M., Garrouch, A., Dunlap, HJ., 1991. Effects of wettability, pore geometry, and stress on electrical conduction in fluid saturated rocks. Log Anal. 32,511 526. SeptembCT lctober. Sherman, M., 1986. A model for the determination of water saturation from dielectric permittivity measurements. In SPWLA 27th Annual Logging Symposium Transactions, Housttm, Texas, June 9—13. Paper E. 

In Equation 19.12, Cq = 8.854 x j-i qi -1 jg jjjg dielectric constant in vacuum, e is the relative dielectric permittivity of the solvent (e = 78.5 for water at room temperature 298 K), and are the electrokinetic zeta potential defined at the shear plane (see Figure 19.3), r is the dynamic viscosity of the solvent (q = 8.91 x 10 kgm" s for water at room temperature 298 K), and E is the externally applied electric field. The first equation in Equation 19.12 represents the fluid motion in a stationary channel under the action of an externally appUed electric field. The motion is called electro-osmosis and the velocity is v. The second equation in Equation 19.12 gives the velocity v, of charged suspended colloidal particle (or a dissolved molecule) driven by the same electric field. This phenomenon is called electrophoresis. The EDL thickness 1/k depends on the concentration of background electrolyte [18,19,25,26]. 

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