Electric saturation effects

Electric saturation effects in the description of neutral solutes in polar media have been strongly advocated by Sandberg et al. [18], who worked out a complete continuum ab initio solvation code containing the e(r) feature and published results of good quality for a large number of solutes. Sandberg et al. remark that PCM calculations do not need corrections for electric saturation, this being due, in their opinion, to the cavity PCM uses. 

This approach has also been applied to saturated C(i) atoms. Due to the much lower polarizabilities of C-H and C-C single bonds, however, the effects are clearly smaller (82), though still detectable. Thus, some effects of substituents X on S-positioned carbon atoms in cyclohexanes and cholestanes were attributed to LEF effects of the C-X dipoles by Schneider and colleagues (76,77,85). The finding that only minor effects are to be expected in saturated molecules was confirmed by INDO-SCF calculations of electric-field effects on l3C chemical shifts of some model compounds performed by Seidman and Maciel (86). These authors conclude, further, that conformational studies on such systems are not promising (86). 

The change of the chemical potential of a component with the field at constant temperature, pressure, and mole numbers is given by Equation (14.75). We note that the electric susceptibility is a function of the temperature, pressure, and mole numbers. It is also a function of the field, but may be taken as independent of the field except for high fields when saturation effects may occur. 

The Mataga-Kakitani (M-K) theory is based on the rather general observation that e.t. processes which show the M.I.R. are mostly charge recombinations and charge shifts, whereas the photo-induced charge separations which start from neutral reactants follow Rehm-Weller behaviour. It is then suggested that the difference is due to the electric field which acts on the solvent in the field of ions or ion pairs, partial dielectric saturation of polar solvents would be reached, and this would restrict solvent motion. No such dielectric saturation effect would exist in the solvent shell of neutral reactants, so that solvent motion remains unhindered. 

In conclusion the contribution to the dielectric response given by the third order susceptibility has different sources with opposite signs. Molecular simulations on ions in solution show that both dielectric saturation and electrostriction effects are presumably present and that for ions with a high charge density electric saturation predominates. This suggestion is in agreement with the general consensus that dielectric saturation is the first element to consider in the description of nonlinearities. 

Beside the strength of electric field, the dynamic yield stress significantly depends on the amount of MWCNT in the composite particles. As can be seen in Figure 8.15, for different field strength the yield stress goes up with rising concentration in different ways. While for 1 and 2 kV/mm, it continuously increases with nanotubes content, at 3 kV/mm a saturation effect can be observed. The presence of MWCNT enhances the conductivity of the composite particles and thus influences their ability to be polarized. If the conductivity of the particles is above a certain limit, the current density in the... 

Electro-optical properties molar r raction and molecular correlation the Kerr effect its component terms and molecular theory molecular angular correlation non-linear polarizability generalized Kerr effect translational and molecular field fluctuations electric saturation. 

The Kerr Effect in Polymer Solutions and Colloids.— Strong electro-optical birefringence is observed in colloidal systems and in macromolecular solutions." Numerous theoreticed papers" have been devoted to the quadratic optical birefringence exhibited by solutions of small macro-molecules in weak electric fields. O Konski et al. and others < - have shown that complete alignment of macromolecules in a static electric field does in fact take place in various macromolecular solutions, permitting the observation of the electric saturation of opticed birefrin nce." ... 

Electric Saturation of the Kerr Effect. When calculating the dectric reorientation function of molecules (172) for molecular gases, it was justifiable to use the approximation (169a) for the perturbed statistical distribution function. In the general case, calcidations have to be carried out with a distribution function of the form (169) where, for axially... 

The imposition of an electric field on a liquid is always accompanied by a flow of electric current (due to conductivity) and dissipation of Joule heat. The ensuing rise in temperature of the liquid can lead to a change in permittivity much in excess of the saturation effect under investigation. 

Comidete Dielectric Saturation.— Our previous considerations have dealt essmtially with permittivity variations Ae( whidi vtere quadratic in the applied strong electric field Ep. The quadratic depraid ce is confirmed by As measurements performed on molecular substances, acted on by moderately strong electric fields. In macromolecular substances. As is no longer quadratic in the field strength as is the case with the Kerr effect," -" complete electric saturation sets in. 

Experimentally, complete electric saturation of electric pomittivity variations has been observed recently, in solutions of dipolar macro-molecules where the effect is negative," and in ones of non-dipolar and weakly dipolar macromolecules where it is positive in the entire range of variability of the electric field strraigth. >... 

In atomic and simple molecular liquids, the Kerr effect, electric saturation, etc., are caused not only by non-linearities directly induced in the atoms and molecules by the external electric field (the Voigt effect), but are primarily due to Yvon-Kirkwood fluctuational-statistical processes. One should keep in mind, however, that the intrinsic electric polarizability of non-dipolar molecules is subject to modification by at least three factors (i) the effect of translational fluctuations, (//) intermolecular attractive or repulsive forces, and (in) non-linearities induced by the tenq>oraIly and spatially fluctuating electric fields of neighbouring molecules. Thus, the Yvonr-Kirkwood process discussed in Section 4 leads, in dipolar approximation, to the following variation of the electric polarizability tensor of a molecule immersed in a statistically noit-uniform medium ... 

This complexity of the saturation phenomenon, though a drawbadr, is at the same time an asset from the theoretical point of view. The reader vrill have noted from the theory discussed above that electric saturation makes directly apparent the participation of reorientation of the electric poles of molecides and macromolecules. In this respect, saturation is unique, owing to the part played in it, in addition to the various molecular processes specific to other effects e.g. the Kerr effect), by entirely new processes provi ng valuable information on the interactions between molecules in condensed phases and their internal structure. We believe it... 

If, as is mostly the case in experiment, the analysing field E and polarizing field Ep are applied in the same direction, the electric permittivity variation tensor (12) possesses but one non-zero component, in the field direction, usually denoted by Ae,( p). This particular case is referred to as the effect of electric saturation in an dectric field. In molecular liquids Ae,( ) is in general a quadratic function of the field strength Ep, as proved r )eat y by Piekara and his co-workers. Lately, Davies has published a review on aspects of recent tfielectric studies, particularly dielectric saturation in liquids and molecular solutions, as well as in solutions of macromolecules where complete dielectric saturation has been observed. 

Obviously, in strongly dipolar substances, the purely dipolar constant will be the predominant one and consequently this treatment of gas theory results in a negative saturation effect. Numerical values of molar non-linear electric field constants (259) are listed in Table 15 for some of the more important non-dipolar as well as dipolar molecules. 

Piekara, A. A theory of electric polarization, electro-optical kerr effect and electric saturation in liquids and solutions, Proc. Royal Soc. London. Series A, Math. Phys. Sci. 172(950), 360-383 (1939)... 

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