Glass-forming low-molecular-mass ferroelectric liquid crystals

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Abstract
For the first time, glass forming low molar mass liquid crystals were synthesized exhibiting ferroelectric properties. This goal was achieved using derivatives of 2,5-dihydroxybenzoic acid with lateral aromatic branches. Several of the compounds prepared show a glass transition near room temperature occurring either in the SmA or in the SmC* phase. In the SmC* phase high values of the spontaneous polarization up to PS approximately equals 200 nC/cm2 are observed. With decreasing temperature the switching time increases by five orders of magnitude from 1 ms to 10 s. Correspondingly, Goldstone mode dielectric relaxation frequencies as low as 10-1 Hz can be observed. In the SmA phase some of the compounds exhibit a very strong electroclinic response, i.e. tilt angles up to 10 degree(s) can be induced near the SmA/SmC* phase transition. The temperature dependence of the soft mode dielectric strength and the relaxation frequencies show strong deviations from simple critical behavior. It is demonstrated that the electrically controlled switching angle can be frozen in. The combination of this strong effect with the distinct second order optical susceptibility exhibited by the materials can be of interest for NLO-applications.

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