Molecular orientation SSFLCs

In the sections on smectic liquid crystals, first the alignment and molecular orientation of surface stabilized ferroelectric liquid crystals (SSFLCs) are treated in detail. Next, the alignment technologies needed for the occurrence of bistability are detailed. Furthermore, liquid crystalline devices made of AFLC materials and the applications of FLC and AFLC materials to active matrix devices are discussed. 

Molecular orientational models of SSFLCs have previously been studied, so the orientational states of SSFLCs and their optical properties are fully understood. For example, the smectic layer structures of various SSFLCs have been studied by using higji-resolution X-ray diffraction and the relationship between the layer tilt angle and the optical molecular tilt angle has been confirmed. 

The molecular orientational states of SSFLCs are classified by the optical viewing conditions and the relationship between the directions of bend of the layer structure and the surface pretilt angle. The molecular orientational models of the states have been considered and illustrated with regard to the experimental results, and useful information has been obtained from optical simulations using the models. The influence of the surface pretilt angle on the orientational and the optical properties of SSFLCs has been described. 

The molecular orientational states of the SSFLCs have been analyzed by polarizing microspectroscopy and optical simulation. The X-ray studies indicated that the chevron layer structure is determined by the bulk properties of the FLC, but the molecular orientation in the smectic layer is strongly influenced by the surface properties. The effect of surface pretilt angle on the molecular orientation and the optical properties of SSFLCs have been studied by the optical simulation based on the molecular orientational models. 

Fig. 5.1.20 Molecular orientational models of SSFLCs with structure.

The orientations of the molecules of the FLC materials are classified by the presence or absence of a helical structure. The most famous FLC device is the SSFLC (Surface Stabilized FLC) [1], in which the helical structure of the FLC material is unwound. While a variety of molecular orientations have been applied in SSFLC devices, three molecular orientations appear to be the most useful in practical FLC displays.These are the bookshelf-layered structure and the Cl-uniform (CIU) and the C2-uniform (C2U) orientations [2]. Each of these structures shows monostability or bistability, depending on the material and its alignment properties. The monostable orientations are applicable to active matrix FLC displays while the bistable orientations are applicable to passive matrix FLC displays. FLC displays with a helical orientation have also been investigated. One useful FLC mode with the helical orientation is the DHF (deformed-helix ferroelectric) mode [3]. This mode is monostable and is thus suitable for an active matrix drive method. 

In a sense, the bookshelf layer structure (shown in Fig. 6.1.3) is the ideal molecular orientation for an SSFLC. One of the greatest merits of the bookshelf layer structure is its wide memory angle. The ideal memory angle in an SSFLC is 22.5° because the transmission of light of a wavelength A is given by the following equation. 

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