Permeability, dielectric

Typically, large-scale gas filling makes the main characteristics of foam plastics — coefficients of heat and temperature conductivity, dielectric permeability, and the tangent of the dielectric loss angle — totally independent of the chemical structure of the original polymer [1],... 

The fundamental electrochemical event, that is, electron transfer, occurs at the electrode surface. Peculiarities of electrochemical reactions include an electrical field, which in a special way complicates the phenomena of adsorption and desorption at the surface. The first layer of the solution, which is in contact with the electrode, possesses a specific structure. It is important for charged particles that the orientation of medium molecules in the vicinity of the electrode produces a decrease in dielectric permeability in the compact part of the double layer (Damaskin and Kryshtalik 1984). 

In recent years investigations were begun in which the variation of adsorbent properties, such as electrical conductivity (1, 2), dielectric permeability (3-5), and linear sizes (6-11), were studied. In these systems the adsorbents were usually active carbons and porous glasses. Only a few studies were carried out on zeolites these studies are interesting because of the perfect porous structures (12-14) of zeolites. All these studies showed that during adsorption the properties of adsorbents do not remain constant. 

These are the Fourier components of the polarization vector which are connected with the oscillations of the ions that are present in eqns. (44)-(46). In addition to this polarization which results from the motion of the nuclei, purely electronic polarization (i.e. the polarization of electrons at equilibrium positions of the nuclei) is also of importance. In the frequency region below the optical range, the purely electronic polarization can be expressed through the optical dielectric permeability (i.e. the dielectric permeability corresponding to the frequencies which are less than those in the optical absorption region, but exceed those of the nuclei vibrations). Optical frequencies considerably exceed those of the nuclear vibrations therefore, in the optical frequency region the nuclei do not, in practice, contribute to polarization. The connection of the Fourier component of purely electronic polarization with that of the induction of the electric field has the usual form... 

Here, and in eqn. (50), summing runs with the fixed k value by the frequencies from various spectrum bands of the normal coordinates. The full polarization can also be expressed through the dielectric permeability s(k,ao)... 

The connection of the coefficients yk with the dielectric permeability i (k,oj) follows from eqns. (47)-(49)... 

Equations (50)-(53) allow one to express the probability of tunneling through the dielectric permeability of the medium. In particular, substituting relationship (54) into eqn. (30) we get the following general equation for the tunneling probability... 

If we further neglect the spatial dispersion of the dielectric permeability, then eqns. (56a) and (56b) are, respectively, transformed into the forms... 

In the right-hand side of this equation the first term takes into account the contributions to the exothermicity that are not associated with the medium, the second and the third terms the contributions from the interactions of the donor and the acceptor cores with the medium in the initial and the final states, respectively, and the fourth term the contribution from the unscreened Coulomb interaction between the donor and the acceptor, zx and z2 being the core charges of the donor and the acceptor, respectively. We must stress that, in the denominator of the last term of eqn. (59) the dielectric permeability of the medium is absent because the effect of the medium is contained in the terms E and E. If the distance between the donor and the acceptor considerably exceeds the sizes of the donor and the acceptor then, using eqn. (58), it is easy to obtain... 

It can be shown [24] that, in this situation, the dependence of the reaction exothermicity on if is also determined by eqn. (60) but with the following corrections for z one has to take not the core charge of the donor, but the full charge of the donor before the electron transfer has taken place for z2 one has to take the charge of the acceptor after the electron transfer has taken place. The dielectric permeability of the liquid solution should again be used as e, in eqn. (60). 

Critical distances [32] of ion stabilization in organic solids for the rectangular, Rrcr, and the Coulomb, Rccr, forms of the barrier for electron tunneling, and critical coefficients, -D, of ion diffusion as functions of the ionization energy, 7d, of the donor, and the static dielectric permeability of a solid,... 

Here, Nc is the number of conductivity electrons containing in unit of volume, cop = (Nce2/m)1/2 the plasma frequency of metal, and E — Eext exp —icot. The real part of coefficient at E in the formula (4) is the part of dielectric permeability s c caused by conductivity electrons (s c — —co2/co2 + r2). Total dielectric permeability s is equal to... 

As is specified in work [17], the system of conductivity electrons in a nanocrystal is similar to the resonator. Thereof electromagnetic field in a crystal can give rise to collective electronic excitations [17], which refer to as surface plasmons as they are caused by charges on a nanocrystal surface in dielectric [16]. At a>v dielectric permeability e (oj) according to the formula (5) is negative. It means that conductivity electrons in a nanocrystal oscillate out of phase with electric oscillations of an external field [16]. 

Optical absorption in M nanocrystals embedded in dielectric matrix depends on characteristics of matrix and interface between matrix and nanocrystals. In the classical model of Mie only macroscopical dielectric permeability of environment e 2 is taken into account [16]. In this model charges at the M nanocrystal surface are determined by s2 and so frequency coa corresponding to a peak of resonant absorption is defined from a relation [18]. 

It should be noted that the given sensor is much more sensitive than a sensor based on composite films CuS-polyvinyl alcohol prepared by a classical liquid-phase method [88]. In these films the sensor effect is caused by increase in probability of tunnel transitions between CuS semiconducting particles owing to increase in macroscopical dielectric permeability of a hydrophilic matrix absorbing water from the surrounding atmosphere [88]. 

Figure 57. In the case of current constriction induced by a partially contacted metal electrode (shown by electrical potential lines in the inset, contact in the center, separation by an air gap otherwise) the impedance response ideally consists of two semicircles. At high frequencies the air gap (cf. distance between curved electrode and plane surface) becomes dielectrically permeable.286 Reprinted from J. Fleig and J. Maier, Electrochim. Acta, 41 (1996), 1003-1009. Copyright 1996 with permission from Elsevier.

Methyltin halides dissolved in solvents of type (i) do not enter into a noticeable donor-acceptor interaction with the solvent the tin coordination number is, therefore, unaffected. At the same time, conductivity techniques (78, 79, 140, 141, 47, 24) show that methyltin halides do not ionize in solvents such as nitromethane and nitrobenzene whose dielectric permeabilities are high (35.9 and 34.8, respectively). In this section the halide structures are discussed only in solvents of type (i). When they are dissolved in solvents of type (ii), the halides enter into complex formation these systems are dealt with under complexation of methyltin halides (see Section IV). 

Of considerable interest is the use of silicone rubbers for insulation in electrotechnical equipment. This is accounted for by superior heat resistance of elastomers and their good dielectric properties. E.g., the dielectric permeability of polyorganosiloxane elastomers at 500 V and 60 Hz is 3.5-5.5, their electric strength at 60 Hz is 15-20 KV/mm, and the dielectric loss tangent, which characterises the losses of electric energy in insulation, at 500 V and 60 Hz amounts only to 0.001. It is very important that these characteristics are preserved in a much wider temperature range than in the case of natural and synthetic organic elastomers. 

In the dc case, the current has to flow to the electrochemically active sites close to the 3PB and a considerable current constriction results (Fig. 22b). Hence, the dc resistance consists of the resistance due to the electrochemical reaction and the bulk resistance, which includes the current constriction in the vicinity of the active ring. At higher frequencies, the inner part of the microelectrode becomes dielectrically permeable and the current flows to the entire microelectrode area (Fig. 22c). In other words, the current lines in the bulk, and thus the bulk resistance, are frequency-... 

With dielectric permeability for the region of crystal lattice vibrations of InSe (e1 = 6.8) and GaSe crystals (e1 = 6.2) [17] it is not difficult to show that appearance of a crystal layer between two H2 molecular sheets lead to screening of their interaction. It results in increase of parameter Ch2 in a matrix of a layered crystal, which becomes practically conterminous with parameter CGaSe and C rlSc in the given crystals. 

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