Electro-optic response

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

To achieve better control of the poling, we have developed an on-line electro-optic monitoring technique . The technique is based on the accumulated change of the electro-optic response when the domains grow through the crystal from the patterned side to the opposite side. A He-Ne beam polarized 45° to the z-axis is launched along the x-axis of the crystal (figure 9). When an electric field is applied, the output polarization state of... 

The classical cholesteric phase materials show only a weak anisotropic interaction with electric fields and hence are of limited use in electro-optical response applications. Cholesteric phases for these outlets are consequently produced by adding chiral dopants to nematic liquid crystals. 

Cowling SJ, Hall AW, Goodby JW (2005) Electro-optic response in a racemic smectic C liquid crystal. Adv Mater 17 1077-1080... 

Most reports over the past 4 years have dealt with the manipulation of display-related parameters such as electro-optic response and alignment, but increasingly also with thermal effects, pattern formation, nanoparticle-liquid crystal compatibility (i.e., enhancing the stability of dispersions), and to some degree with nanoparticle organization. 

Several other groups reported interesting combinations of experimental and theoretical results on the alignment and electro-optic response of CNTs in thermotropic nematic liquid crystals [ 467—469]. However, lyotropic liquid crystals should... 

In materials that possess both photoconductive and electro-optic responses, the photo-generation and trapping of charge carriers produces internal fields that modify the refractive index. A sinusoidally varying intensity caused by the... 

The field of photorefractivity in organic polymers and glasses has been in existence for less than a decade. The understanding of charge generation in these materials (which are often composites) is not yet mature, and the behavior of some of the more common constituents is understood better. Much of the literature on photo-refraetivity deseribes free earrier generation quantum efficiency measurements only briefly, before a more detailed discussion of other factors such as mobility and electro-optic response. Some of the relevant information pertinent to free carrier generation in these materials is presented here, to be followed by a review of this aspect of the amorphous photorefractives literature. 

AODCST, 2-[4-bis(2-methoxyethyl)amino]benzylidene malononitrile PTPDac-BA2, copolymer, 65% wt N-(4-acryloyloxymethylphenyl)-N -phenyl-N,N -bis(4-methylphenyl)-[ 1,1 -biphenyl]-4,4 -diamine, 35% wt A-butylacetate DOP, dioctyl phthalate DRl-DCTA, 4,4 -di(carbazol-cl-yl)-4"-(2- N-ethyl-N-[4-(4-nitrophenyldzo)phenyl]amine ethoxy)-triphenylamine other abbreviations are defined in the text and Figures, quantum effieieney of mobile charge photogeneration has been estimated where necessary, °a relative static dielectric constant of 3 and a linear electro-optic response have been assumed. 

Figure 24. Electro-optic responses as a function of frequency. (Reprinted with permission from (M. Thakur, A. Mishra, J. Titur and A.C. Atiyi, (2002) Appl. Phys. Lett, 81, 3738). Copyright (2002), American Institute of Physics)...

Fig. 17 Temperature dependence of electro-optical response time for the polymer-stabilized blue phases (polymer fraction a = 6.3, 10.5, 15.0 mol %) in the rise process (A) and decay process (B) [46]...

The colloid particle or polyelectrolyte molecule may possess a permanent dipole moment. Considerable influence of this moment on the magnitude and the sign of the electro-optical effect is expected in the range of particle rotation. Discrimination between the induced and the rotational relaxation of the particles can be reached, however, since the electro-optical response to a sinusoidal electric field is the sum of a time-independent term adc and a term a2rjJ that is sensitive to the particle rotation [24,45]. The critical frequency of the alrjJ relaxation depends on the rotational diffusion coefficient Dr of the particle, while the critical frequency of relaxation of the time-independent term adc depends on the translational diffusion coefficient of the ions moving on the particle surface. 

This reduction in the number of contacts comes, however, at a price. As the matrix increases in size (say, to n rows), the fraction of the frame time dedicated to each line decreases to 1/n. The rest of the frame time ((n— l)/n), each row sees signals intended for other pixels. This degrades the selection ratio and reduces the field contrast available for effecting the desired electro-optical response [129]. One solution to this problem is to introduce a latching... 

Ferroelectric liquid crystals (FLC) are of great interest due to their fast electro-optical response which is about 1,000 times faster than conventional twisted nematic cells [131]. The geometry used is called a surface stabilized FLC cell which utilizes a very thin gap (=2 pm) to unwind the FLC supramolecular pitch (=1-2 pm) since the bulk FLC materials do not show macroscopic polarization. This very thin gap, however, leads to difficulties in manufacturing large panels and very poor shock resistance. Researchers have proposed the concept of microphase stabilized FLC [79,109, 130] using FLC-coil diblock copolymers for electro-optical applications as shown in Fig. 15. This concept takes advantage of ferroelectric liquid crystallinity and block copolymer microphase separation since the block... 

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