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Mechanisms of polarization

In general, there are five different mechanisms of polarization which can contribute to the dielectric response [3], [Pg.15]

The total polarization of dielectric material results from all the contributions discussed above. The contributions from the lattice are called intrinsic contributions, in contrast to extrinsic contributions. [Pg.15]

Each contribution stems from a short-range movement of charges that responds to an electric field on different time scales and, hence, through a Fourier transform, in different frequency [Pg.15]

The dispersion of the dielectric response of each contribution leads to dielectric losses of the matter which can be mathematically expressed by a complex dielectric permittivity  [Pg.16]

Dielectric losses are usually described by the loss tangent e  [Pg.16]


Wertheim M 1979 Equilibrium statistical mechanics of polar fluids Ann. Rev. Phys. Chem. 30 471... [Pg.558]

The dielectric constant is a measure of the ease with which charged species in a material can be displaced to form dipoles. There are four primary mechanisms of polarization in glasses (13) electronic, atomic, orientational, and interfacial polarization. Electronic polarization arises from the displacement of electron clouds and is important at optical (ultraviolet) frequencies. At optical frequencies, the dielectric constant of a glass is related to the refractive index k =. Atomic polarization occurs at infrared frequencies and involves the displacement of positive and negative ions. [Pg.333]

The fact that dynamic 13C polarization is only possible through the indirect way via tire 1H spins suggests the mechanism of polarization transfer. Since the polarization transfer between the electrons and nuclei are driven by the dipolar interactions between them, and the fraction of the guest triplet molecules was small, it would be natural to assume that the polarization of the electron spins in the photo-excited triplet state is given to those H spins which happen to be close to the electron spins, and then the 1H polarization would be transported away over the whole volume of the sample by spin diffusion among the 1H spins. [Pg.381]

The sorption of n-butyl alcohol and (err-butyl alcohol on phenyl modified MCM-41 type sorbent having pores of approximately 20 A diameter (i.e. in the microporous range), has been studied. Comparison of butanol sorption with nitrogen, water, and benzene sorption data indicates that steric hindrance significantly affects the sorption of n-butyl alcohol by the microporous silica, far more so than for tert-butyl alcohol. The different shapes of the isotherms obtained on the microporous material (Type I for fert-butyl alcohol, Type IV for 71-butyl alcohol) suggest that the preferred mechanism for adsorption of leiY-butyl alcohol is via organic interactions with surface phenyls, whereas for n-butyl alcohol, a mechanism of polar interaction is more likely. [Pg.617]

So far we have considered various radiational and collisional mechanisms of polarization of molecules. There exist earlier methods applying the action of an external stationary magnetic, later of an external electrostatic, field to beam molecules for producing anisotropic distribution of the angular momentum J and of the molecular axis. [Pg.231]

The inductive effect of an inorganic, organic or organometallic substituent, Y, is characterized quantitatively by several widespread constants, such as a and others (a, a, F etc.)34,57. The relationship ai(Y) = ct (Y) = F(Y) = 0.45inductive constant a of a certain Y substituent (Table 5) reflects several electronic interactions. The most important independent mechanisms of polarization of bonds between the substituent Y and the reaction centre are the field and the inductive interactions. The contribution of each mechanism depends on the type of substituent Y29. [Pg.140]

Of direct relevance to the debate described above, Skidmore examined extensively the mechanism of polarity reversal catalysis described in Scheme 11 and concluded that the key step (step 2, Scheme 11) in the proposed mechanism, namely the transfer of hydrogen atom from a trialkylsilane to a thiyl radical, is severely endothermic54,55. [Pg.359]

The mechanism of polar copolymerization (Figures 4-22 and 4-23) involves in the first step binding of the non-polar or polar monomer to the catalyst. In the standard Coose-Arlman mechanism117,118 for a-olefin polymerization the monomer insertion follows the complexation of the olefin by its double C=C bond (TT-complex,... [Pg.254]

The 1,5-biradicaI BRi formed during the Patemo—Biichi reaction of excited benzo-quinone B with quadricyclane Q (for the formulas, see Chart 9.4) provides one of the extremely rare examples of a short-chain biradical that produces CIDNP of the radical pair type. Extracts of the CIDNP spectra are displayed in Fig. 9.7. The occurrence of both absorption and emission in the same product is clear evidence for this mechanism of polarization generation. [Pg.200]

Fig. 20 Mechanisms of polarity inversion in a dielectric, (a) Electric polarization (b) ionic polarization (c) orientation polarization. Fig. 20 Mechanisms of polarity inversion in a dielectric, (a) Electric polarization (b) ionic polarization (c) orientation polarization.
Scheme 4.9 Proposed mechanism of polarity reversal catalysis using the (TMS)3SiH-thiol system. Scheme 4.9 Proposed mechanism of polarity reversal catalysis using the (TMS)3SiH-thiol system.
Several possible mechanisms of polar nucleophilic photosubstitution in an aryl derivative 238 are portrayed in Scheme 6.93. The first, unimolecular nucleophilic photosubstitution mechanism (SN1 Ar where 1 denotes first-order kinetics), in which an excellent leaving group (X) is heteroly tic ally detached from excited state to form a relatively unstable aryl cation and is subsequently attacked by a nucleophile, is rarely observed.836 838... [Pg.288]

FIGURE 3.2.3 Frequency dependence of the dielectric constant and mechanisms of polarization. [Pg.232]

FIGURE 2.24 Mechanisms of polarization. (Reprinted from Zlotorz3fnski, A., Crit. Rev. Anal. Chem., 25,43-76, 1995. With permission from Taylor and Francis Group.)... [Pg.67]

Almost all the formalism and the approximation schemes of Sections II and III have a natural extension to systems of polarizable dipolar particles, but the precise details of the extension depend on the way polarizability is introduced into the Hamiltonian. We refer to the two quite distinct Hamiltonian models that have been most thoroughly developed in this context as the constant-polarizability model and the fluctuating-polarizability model. The dielectric behavior of the former was first systematically investigated from a statistical mechanical viewpoint by Kirkwood and by Yvon, who considered the model almost exclusively in the absence of permanent dipole moments. (Kirkwood S subsequently pioneered an exact formulation of the statistical mechanics of polar molecules, but largely as a separate enterprise that did not attempt to treat the polarizability exactly.) The general case of polar-polarizable particles remained only very partially developed ... [Pg.273]

Peter, T. (1996) Formation mechanisms of polar stratospheric clouds, in Nucleation and Atmospheric Aerosols 1996, M. Kulmala and P. E. Wagner, eds., Elsevier, Oxford, UK, pp. 280-291. [Pg.202]

Weintraub, Goodman Akeson (2000). It is useful to present a short review of the primary mechanisms of polarization of light by young stars. [Pg.310]

The most polar components of an RP-HPLC mobile phase will often be water (HOH), acetonitrile (CH3—C=N), or methanol (CH3OH). The polarity of the mobile phase can be adjusted to values between these by mixing them in different proportions. Even less-polar compounds, such as ethanol, tetrahydrofuran, or diethyl ether, may be added to bring the overall eluent polarity down even more, or to introduce different interaction mechanisms of polarity which may increase the separation factor a between close pairs of analytes. Being at the extreme end of the polarity scale, water is often considered the fundamental component of the mobile phase mixture, and the other less-polar, organic solvents which may be added are termed organic modifiers ... [Pg.804]

Omelchenko, T, Vasiliev, J.M., Gelfand, I.M. et al. (2002). Mechanisms of polarization of the shape of fibroblasts and epithefiocytes Separation of the roles of microtubules and Rho-dependent actin-myosin contractflity. Proc. Nad. Acad. Sci. U.S.A. 99,10452-10457. [Pg.302]

Figure 3.58 shows a curve of the variation of the dielectric constant (relative permittivity) with firequency for a hypothetical solid dielectric having aU four mechanisms of polarization. Note that except at high frequencies the electronic mechanism makes a relatively low contribution to permittivity. However, in the optical range of firequencies, only this mechanism and the ionic mechanism operate they therefore strongly influence the optical properties of materials. [Pg.352]


See other pages where Mechanisms of polarization is mentioned: [Pg.337]    [Pg.149]    [Pg.132]    [Pg.289]    [Pg.316]    [Pg.304]    [Pg.36]    [Pg.15]    [Pg.189]    [Pg.193]    [Pg.126]    [Pg.183]    [Pg.200]    [Pg.177]    [Pg.182]    [Pg.1248]    [Pg.145]    [Pg.419]    [Pg.355]    [Pg.203]    [Pg.1120]   


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