Frustration between Ferro- and Antiferro-Electricity and its Application to Liquid Crystal Displays

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The V-shaped switching has attracted attention because of its potential applications to fast-response AM-LCDs. Two companies have developed a group of materials, which are closely related to the prototyped antiferroelectric liquid crystals. This research aims at understanding what are essential to the emergence of the practically usable V-shaped switching. Two essentials are: ( 1 ) the frustration between ferro- and antiferro-electricity, and ( 2 ) the "biaxial anchoring", i.e. a tendency that the more easily polarizable short axis (intuitively, the averaged direction of phenyl ring planes) is liable to become rather perpendicular than parallel to the substrate plates. Since it is parallel to the tilt plane in the V-shaped switching materials, the melatopes may emerge parallel to an electric field even in ferroelectric SmC*, and the biaxial anchoring on polyimide aligning films plays an important role, destabilizing the SS states; the total anchoring becomes almost independent of the a … More zimuthal angle specifying the position on the SmC* tilt cone. The relatively weak anchoring due to rubbing must force to align directors. When the chiral twisting power is large, the distribution around the rubbing direction may become broad. The first essential, i.e. the frustration assures the extreme softness with respect to the tilting direction and hence the hysteresis-free characteristics by easily forming invisible microdomains in the whole switching range. The biaxial anchoring may destroy the antiferroelectric SmC_A* structure. The local director shows a variety of orientational distributions at the tip of the V; neither Langevin-like reotientation nor highly collective azimuthal angle rotation of in-layer directors is essential to the V-shaped switching. Extremely large spontaneous polarization and the resultant polarization charge stiffening of the orientation field is not necessary. Any twisting structure of the smectic layer as well as the director caused by interface effects rather degrades the practical performance of the V-shaped switching. Less