The Magnitude of the Spontaneous Polarization in Two Ferroelectric Liquid Crystals

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Abstract
The spontaneous polarization was measured for two chemically isomeric ferroelectric smectogens that have different phase sequences. The two compounds, S-4-(3,‘7’-dimethyloctyloxy) phenyl 4-n-decyloxybenzoate and S-4-n-decyloxyphenyl 4-(3,‘7’-dimethyloctyloxy) benzoate differ only in the direction of the central ester linkage. Thus, both materials have similar dipolar characters. The first material exhibits a smectic A to smectic C* phase transition, whereas the second exhibits a cholesteric to smectic C* phase change. The optical tilt angle for the first compound saturates, close to 22 degrees in the smectic C* phase, whereas the second has a relatively large temperature independent value of approximately 45 degrees. Concomitantly, the magnitude of the spontaneous polarization of the first material is less than that of the second. The temperature dependence of the polarization of these materials was also measured. It is concluded for materials that are isomeric that the relative size of the polarization is dependent on the magnitude of the tilt angle in the ferroelectric phase, however a quantitative relationship could not be established.