Dipolar reorientation

Fig. 4 Dipolar reorientational time correlation function, Cw(t) for bound water molecules in the micellar solution, and for bulk water molecules.

There are at least two ways to obtain information by t.s.c. The first is that for the global spectra where the polymeric film is polarized by a static electric field at the polarization temperature Tp and then quenching down to the freezing temperature. With the field turned off and the sample short circuited the depolarization current due to dipolar reorientation is measured as the temperature increases from T0 to the final temperature Tf > Tp. 

Much of the research on solvation dynamics has been devoted to polar solute-solvent systems. In these media, it has been found that the response to a change in solute dipole is due primarily to collective solvent reorientation and that it can be predicted reasonably well using information on pure solvent dipolar reorientation, for example, from dielectric permittivity measurements, as input [1,6,7,9],... 

Thus, in dealing with a macromolecular solution exhibiting strong dipolar reorientation, we have a variation (319) of the form ... 

Because electrolyte relaxation, that is, the translational diffusion of ions, occurs at a slower time scale and is physically distinct from the dipolar reorientation, it is convenient to view it as a separate coordinate of the van der... 

Polarization current—caused by dipolar reorientation and accumulation of opposite charges at the electrodes and possible interfaces in the polymer (Friedrich et al. 1997, Wasylyshyn et al. 1996). Maxwell-Wagner-Sillars polarization arises in interfaces of heterogeneous systems like nanocomposites. 

If a dielectric material is suddenly placed in an electric field, the permanent molecular dipoles in the dielectricum will attempt to orientate. The orientation occurs by a random process, that is, via diffusion or jumps. The applied electrical field, of course, influences the mean orientation more than the reorientation of the individual molecular dipoles. Since molecular dipolar reorientation is coupled with reorientation of molecules or molecular groups, the time required for macroscopic reorientation corresponds to that for the reorientation of the molecules or groups. 

The suggestion by Cain that the effect occurs through an actual dipolar reorientation would require unusually large field strengths or extremely large dipole moments. The prediction of an inhibitory effect due to membrane hyperpolarization because of increased steady-state potassium conductance concomitant with decreased steady-state sodium conductance certainly should merit enough attention to design experiments to test the existence of such a response. 

A further crucial consideration is the possible, but unsubstantiated, effect of dipolar reorientation. Dorn (12) has suggested that the polar head group could reorient under the field of an ion. Such a process would yield a decrease of the overall barrier to ion transport. If the dipole is completely free to rotate under the influence of temperature, the interaction energy would be... 

Figure 13 shows the dependencies of the change in A eff and on frequency (/) of the imposed field for SNE-7 [18]. The two effects have a similar dependence on/. Neither EO nor EM effects are observed at frequencies above 10 Hz. When/is too high, it does not induce a dipolar reorientation of the mesogens, as in the case of LMM-LCs. At frequencies less than 10" Hz, the EO and EM effects become pronounced. At low frequencies, the deformation and the change in A eff increases with/. This may be because of a reduction in the effective voltage amplitude caused by an ionic current of impurities that becomes appreciable at low frequencies. 

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