Orientation by an electric field

The integral over is carried out analytically by using the fact that K is large for example, 

Since rodlike polymers have a large optical anisotropy, they have a significant depolarized light scattering, which is particularly suitable for studying rotational diffusion. In the small-angle regime k L 1, the dynamic structure factor is written as  

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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. 

Linear dichroism data with DNA oriented by an electric field [53, 54] or a linear flow [55, 56], under linearly polarised light, lead to determinations of the angle between the absorbing transition dipole moment of the chromophore in the molecule and the DNA helix axis conclusions concerning intercalation may thus be drawn from this technique. Finally, with chiral compounds, circular dichroism is also an attractive method to determine the enantioselectivity in the binding of the molecule [48, 57,58]. 

Although the basic principle dates back to the early days of nonlinear optics [59], it was only implemented three decades later with chromophores oriented by an electric field in solution [60, 61]. The chromophore was Foron Brilliant... 

Positive Cotton effects (c.d.) are reported for both 3a- and 3/8-trimethylstannyl-5a-cholestanes, at 203 nm and 210 nm, respectively.35 The compounds were studied in connection with an evaluation of the effects of /3 -trimethylstannyl substituents in cyclohexanone analogues, which provide evidence of through-bond coupling to augment that already recognized for electronegative substituents.36 The circular dichroism associated with the enone systems of cholest-4-en-3-one and 3/3-acetoxycholest-5-en-7-one has been recorded for samples oriented by an electrical field in a nematic phase composed of cholesteryl chloride and cholesteryl laurate.37 New rules are proposed for the correlation of D-Iine molecular rotations with structures of steroid derivatives.38 This work extends an earlier analysis39 and in the present case relates mainly to data for substituents at C-3, C-5, and C-6. 

The polarization direction of an electronic transition may be determined by measurement of the absorption of polarized light by aligned molecules. (Cf. Michl and Thulstrup, 1986.) Orientation may be achieved in a number of ways. When single crystals are used or when the molecules of interest are incorporated into appropriate single crystals, a very high degree of orientation can be obtained if the crystal structure is favorable. Other methods accomplish orientation by embedding the molecules in stretched polymer films (polyethylene, PVA Thulstrup et al., 1970) or in liquid crystals further possibilities are orientation by an electric field (Liptay, 1963), or, in the case of polymers such as DNA, by a flow field (Erikson et al., 1985). 

Figure 1-5 If polar molecules, such as HF, are subjected to an electric field, they tend to line up very slightly in a direction opposite to that of the field. This minimizes the electrostatic energy of the molecules. Nonpolar molecules are not oriented by an electric field. The effect is greatly exaggerated in this drawing.

There is a good correlation between the strength of the attractive interactions and the amplitude of the electrical birefringence signals as well as the electrical conductivity variation around the percolation threshold [23]. This is because when attractive interactions are present, the formation of droplet aggregates is favored. These aggregates are anisotopic and are easily oriented by an electric field. They also promote percolation at lower volume fractions than for a hard sphere. This is discussed in more detail in Sec. II. B. 

Figure 5. Cell for thermal polymerization of a 50-fim film of a liquid crystal monomer orientated by an electric field...

Structure of dimethylsulfoxide and its orientation by an electric field. Polarized Raman spectroscopy can be employed for investigating the molecular orientation under the field. 

Polarizability p6-ls- rl-zo- lbi-lo-te n [F polariser, fr. NLpolfln spolar] (1811) The ease by which the particles of a substance may be distorted or oriented by an electric field. 

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