Interpretation of the Appearance of the Antiferroelectric Phase in Smectic Liquid Crystals and the Application for Display Device

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To clarify the cause of the appearance of the antiferroelectricity in smectic liquid crystals, we perfored two kinds of experiments : (1) We drew phase diagrams of binary mixtures which show the antiferroelectric phase in order to discuss the strength of antiferroelectricity. (2) We measured the higher order X-ray diffraction due to smectic layr order, determined the layr order parameter and discussed the cause of the antiferroelectricity from the microscopic point of viewWe constructed conoscopic observation system using CCD camera and image processor. Using this system, we drew phase diagrams of binary mixtures, one of which has stronger antiferroelectric strengh and the lest of which has stronger ferroelectric strengh. Based on the diagrams, we proposed the model of "devil's staircase", i.e., emergence of various subphases due to the competition of ferroelectricity stabilized by excluded volume effect and antiferroelectricity stabilized by molecular dimerization.We accurately measured the higher order X-ray diffraction due to the smectic layr structure and determined the layr order parameter, then found that the order parameter increases discontinuously at the phase transition point from smC** to SmCA**. This fact suggests that the layr structure is no longer sinusoidal as usual, but is somewhat one-dimensional lattice in the antiferroelectric phase. We also clarified that the layr thickness in SmCA** is thinner than that in SmC**. These facts supports the model of molecular dimerization as the cause of the appearance of antiferroelecticity