Orienting effect of electric field

The likelihood of the medium being frozen by the electric field is given by the Lan-gevin function resulting from statistical theories which quantify competition between the orienting effect of electric field and disorienting effects resulting from... 

After consideration of the history and position of microwaves in the electromagnetic spectrum, notions of polarization and dielectric loss will be examined. The orienting effects of electric fields and the physical origin of dielectric loss will be analyzed, as also will transfers between rotational states and vibrational states within condensed phases. 

Effects of Electric Field Orientation of Molecules in a Magnetic Field... 

Observations between crossed polarizers of the effects of electric fields on the optical properties of butyl p-anisylidene-pf-amino-cinnamate (BA AC) have demonstrated the existence of a domain pattern which, in contrast to the cigar-shaped patterns of p-azoxyanisole, is circular. These circular domains have their optic axis parallel to the applied field, while in p-azoxyanisole the optic axis is essentially perpendicular to the field. Measurement of the polarization as a function of applied field in nematic BAAC has yielded hysteresis loops similar to those found in ferroelectric crystals. This evidence for a spontaneous polarization indicates that in a material such as BAAC with a dipole moment essentially along the molecular axis the molecules are predominantly oriented in one direction within the domains. 

An extension of rubber elasticity (i.e. of the description of large, static and incompressible deformations) to nematic elastomers has been given in a large number of papers [52, 61-66]. Abrupt transitions between different orientations of the director under external mechanical stress have been predicted in a model without spatial nonuniformities in the strain field [52,63]. The effect of electric fields on rubber elasticity of nematics has been incorporated [65]. Finally the approach of rubber elasticity was also applied recently to smectic A [67] and to smectic C [68] elastomers. Comparisons with experiments on smectic elastomers do not appear to exist at this time. Recently a rather detailed review of the model of an-... 

The primary molecular-mechanical effects of electric fields involve (a) the orientation of permanent dipoles or of dipolar parts in a more complex structure, in the direction of the applied field (b) the deformation of... 

Let us first give a qualitative picture of the Fredericks transition. When a plane light wave falls at normal incidence on a homeotropic cell the electric field of the wave is exactly perpendicular to the director. At a positive value of it would be energetically favorable to orient the director in the direction of the field. However, this is prevented by the homeotropic orientation of the director by the curvette walls. Furthermore, in the first approximation in the light intensity the orientational effect of the field on the unperturbed director is absent, in other words, for E=e,E,j the function exact solution to equation (5). 

Liquid crystalline solutions as such have not yet found any commercial uses, but highly orientated liquid crystal polymer films are used to store information. The liquid crystal melt is held between two conductive glass plates and the side chains are oriented by an electric field to produce a transparent film. The electric field is turned off and the information inscribed on to the film using a laser. The laser has the effect of heating selected areas of the film above the nematic-isotropic transition temperature. These areas thus become isotropic and scatter light when the film is viewed. Such images remain stable below the glass transition temperature of the polymer. 

The general problem of the orienting effect of a static electric field (orientation of polar molecules) was first considered by Debye [6, 7], Frolich [8], and more recently Bottcher [9,10]. 

This macroscopic theory justifies the complex nature of the dielectric permittivity for media with dielectric loss. The real part of the dielectric permittivity expresses the orienting effect of the electric field with the component of polarization which fol-... 

All of the interaction mechanisms described above are expected to produce electric fields in the solute cavity. In the case of specific interactions and reaction field effects these electric fields are expected to have some specific orientation with respect to the solute coordinate system. Dispersion forces and Stark effects are not expected to have any specific orientation with respect to the solute. Magnetic field effects seem unlikely to be important in light of the well-known invariance of coupling constants to changes of the external magnetic field. However, it is conceivable that a solvent magnetic reaction field might... 

Fluorine incorporation either increases the orientation polarization or has little or no effect on it. The former arises from nonsymmetric placement of fluorine atoms relative to an axis of rotation. 2 The nonsymmetric fluorine increases the overall dipole moment, and the groups to which the fluorine is attached can then orient in an electric field. Thus the dielectric constant of a polymer can actually be increased by fluorine incorporation in these instances (see Figure 13.3 and 13.4). 

Stuerga, D.A.C. and Gaillard, R, Microwave athermal effects in chemistry a myth s autopsy 2. Orienting effects and thermodynamic consequences of electric field, J. Microw. Power Electromagn. Energy, 1996, 31, 101. 

The dynamics of block copolymers melts are as intriguing as their thermodynamics leading to complex linear viscoelastic behaviour and anisotropic diffusion processes. The non-linear viscoelastic behaviour is even richer, and the study of the effect of external fields (shear, electric. ..) on the alignment and orientation of ordered structures in block copolymer melts is still in its infancy. Furthermore, these fields can influence the thermodynamics of block copolymer melts, as recent work has shown that phase transition lines shift depending on the applied shear. The theoretical understanding of dynamic processes in block copolymer melts is much less advanced than that for thermodynamics, and promises to be a particularly active area of research in the coming years. 

Second-order optical nonlinearities result from introduction of a cubic term in the potential function for the electron, and third-order optical nonlinearities result from introduction of a quartic term (Figure 18). Two important points relate to the symmetry of this perturbation. First, while negative and positive p both give rise to the same potential and therefore the same physical effects (the only difference being the orientation of the coordinate system), a negative y will lead to a different electron potential than will a positive y. Second, the quartic perturbation has mirror symmetry with respect to a distortion coordinate as a result, both centrosymmetric and noncentrosymmetric materials will exhibit third-order optical nonlinearities. If we reconsider equation 23 for the expansion of polarization of a molecule as a function of electric field and assume that the even-order terms are zero (i.e., that the molecule is centrosymmetric), we see that polarization at a given point in space is ... 

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