Electrooptic Behavior

Knowledge of the electrooptic behavior of the FLCPs is of the utmost importance for display device applications. One relevant parameter in this respect is the response time. As for the spontaneous polarization, the determination of the response time requires a uniformly aligned sample. The test cell is placed between crossed polarizers so that one tilt direction is parallel to the direction of one polarizer. The electrooptic effect is achieved by applying an external electric field across the cell, which switches the side chains from one tilt direction to the other as the field is reversed. A photodiode measures the attenuation of a laser beam when the cell is switched between the two states. Generally, the electrooptical response time is defined as the time corresponding to a change in the light intensity from 10 to 90% when the polarity of the applied field is reversed ( 10-9o)- 

Several switching processes have been identified for FLCPs  

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This chapter describes the most important physical parameters which mainly determine the electrooptical behavior of liquid crystal cells. According to existing phenomenological theories we first ... 

The interaction of liquid crystals with neighbor phases (gas, liquid, solid) is a very interesting problem relevant to their electrooptical behavior. The structure of liquid crystalline phases in close proximity to an interface is different from that in the bulk, and this surface structure changes boundary conditions and influences the behavior of a liquid crystal in bulky samples. The nematic phase is especially sensitive to external agents, in particular, to surface forces, and the majority of papers devoted to the surface properties of mesophases have been carried out on nematics. In addition, the nematic phase is of great importance from the point of view of applications in electrooptical devices. Thus, in this chapter, we will concentrate on surface properties of nematics, though the properties of the other phases will not be skipped either. 

The polar order results in the appearance of the macroscopic surface electric polarization which is the dipole moment of a unit volume of a surface layer (and equal to the surface charge density). The electric polarization can influence the electrooptical behavior of liquid crystals via linear-in-field coupling of the polar director L and the electric field. 

In this section, we would like to discuss only the principal approaches to measurements of the anchoring energy. The best results have been obtained with field-on techniques. However, their consideration requires the knowledge of the electrooptical behavior of hquid crystals which is to be discussed in the following chapters. Here we will only list the most important approaches and show some interesting examples. 

The electrooptical behavior of quasi-homeotropic oppositely pretilted nematic layers has been investigated [11]. In these layers, due to the boundary conditions... 

The electrooptical behavior of PDLC films can be described as follows. 

In this section we will consider another type of nonuniform liquid crystal structures in nematics. These structures are created by a spatially nonuniform electric field, and have nothing in common with the modulated orientational and electrohydrodynamic patterns discussed above which, in fact, were created as a result of self-organization. A spatially nonuniform electric field exists in an electrooptical cell in many important cases such as, photosensitive liquid crystal cells [152-154], spatial light modulators with matrix addressing [152], liquid crystal defectoscopy of surfaces [155], liquid crystal microlens [156], etc. By analyzing the liquid crystal electrooptical behavior in a nonuniform field we can estimate different characteristics of the layer, in particular, sensitivity (i.e., the intensity of the optical response at a given voltage), spatial resolution, etc. 

The main physical parameters which define FLC electrooptical behavior are as follows ... 

Chiba, R. Nishio, Y. Electrooptical behavior of liquid-crystalline (hydroxypropyl) cellulose / inorganic salt aqueous solutions. Macromolecules. Vol. 36, No. 5, pp. 1706-1712. 

M. Ito, Y. Teramoto, and Y. Nishio, Electrooptical behavior of aqueous (hydroxypropyl)cellulose liquid crystals containing imidazolium salts. Biomacromolecules 13, 565-569 (2012). 

D. Kang, J.E. Maclerman, N.A. Clark, A.A. Zakhidov, R.H. Baughman, Electrooptic behavior of liquid crystal filled silica opal photonic crystals Effect of liquid crystal alignment, Phys. Rev. Lett., 86, 4052 (2001). 

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