The Surface-Stabilized State

To obtain fast LC photoresponse, a new guest/host system was developed, in which ferroelectric LCs (FLCs) were used as a host LC. FLCs exhibit spontaneous polarization (Ps) and show microsecond responses to change in applied electric field (flip of polarization) in a surface-stabilized state.1261 If a flip of polarization of FLC molecules in the surface-stabilized state can be induced by light in the presence of an applied electric field, photoresponse in the microsecond time region might be achievable. 

A mixture of an azobenzene derivative and an FLC (Figure 2), in which the concentration of the azobenzene guest was 3 mol%, was prepared in the surface-stabilized state in a very thin LC cell. Then the mixture was irradiated with light at 366 nm to cause trans-cis photoisomerization of the azobenzene guest molecule. It... 

Photochemical control of properties of SmC LC phase was achieved by doping azobenzene A-4 possessing a chiral carbon atom to a ferroelectric LC A-5 [61]. When the SmC LC is in the surface stabilized state, the bulk dipole moment can be flipped by an external electric field. As the hysteresis curve for the Z form is narrower than that of E form, irradiation of UV light to cause E-... 

Ferroelectricity in SmC liquid crystals is directly observed in the surface-stabilized state in which macroscopic domains of opposite tilt direction are connected to opposite directions of the spontaneous polarization cf. Sect. 1.2). An electric field-induced reversal of the direction of spontaneous polarization also reverses the direction of tilt and thus leads to a polar bistable electro-optic response. In thermotropic SmC liquid crystals this unique combination of a fluid ferroelectric material was and is extensively studied. 

The SmC analog nature of the lyotropic phase was demonstrated by the observation of characteristic textures associated with the thermotropic SmC phase, such as broken fan-shaped texture, schlieren texture, zigzag defects, spontaneous tilt domains in the surface-stabilized state and pitch lines. Further evidence was provided by X-ray experiments. The two-dimensional dififaction pattern of an aligned sample confirms that the phase is lamellar, tilted and fluid. 

Figure 17. Spontaneous ferroelectric domains appearing in the surface-stabilized state.

Macdonald, R., J. Schwartz, and H. I. Eichler. Laser-induced optical switching of a ferroelectric hquid crystal. Int J. Nonlinear Opt Phys. 1 103 Ouchi, Y., H. Takezoe, and A. Fukuda 1987. Switching process in ferroelectric liquid crystals Disclination dynamics of the surface stabilized states. Jpn. J. Appl. Phys. 26 1. 

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