Polar alignment

Here we have used the zero-field nematic distribution function PQ( ) for convenience of notation. The degree of net polar alignment can be seen to be enhanced in the liquid crystal over the isotropic case. The limiting cases are isotropic distributions and the Ising model (in which only 6=0 and 6=n are allowed orientations). By retaining only the leading terms in the last equation one sees that in the high temperature limit... 

Figure 3. Time dependence of harmonic generation (of polymer/guest induced polar alignment and relaxation) when the laser intensity is overly strong. The poling-field time dependence is depicted at top. (Reproducedfrom Ref. 23. Copyright 1983, American...

Figure 5. Crystal packing of the 1,3-CHDMn(CO)3--(thiourea)3 complex illustrating the polar alignment. The qrstal structure is isomorphous with the chromium complex shown in Figures 2 and 3.

Churikov, V. M., Hung, M. F., Hsu, C. C., Shiau, C. W, and Luh, T. Y. (2000). Encoding of macroscopic second order nonlinearity via all-optical polar alignment in substituted nor-bornene polymer thin films. Chem. Phys. Lett. 3 2, 19-25. 

Polar alignment resulting from this process establishes C ov symmetry in the medium. There are two unique directions in the point group, the polar direction X and the direction perpendicular and cylindrically symmetric with respect to the X direction. When the common assumption that frequencies and the Cartesian axes along which they are applied can be freely interchanged in lossless media is invoked, only two nonequivalent tensor components exist. 

Polar alignment can be described physically through a knowledge of the orientational distribution function f ) (32). A related quantity that can be expressed as a single number is the order parameter. The order parameter describing the induced polar alignment G is given by... 

Therefore, an appropriately designed anisotropic medium could enhance (or retard) polar alignment. 

For LB multilayers, the main issue is the control of film symmetry through deposition characteristics. Polar alignment can be achieved through molecular design and synthesis. 

FIGURE 10.20. EL spectra of a thermally aligned ITO doped-PI PF2/6 Ca LED with the polarizer aligned parallel (filled circles) or perpendicular (open circles) to the rubbing direction. Inset Luminance-voltage characteristics for devices with doped (filled squares) and undoped (open circles) PI layers. (From Ref. 4.)... 

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