Influence of spacer length on dielectric properties of polymeric liquid crystals

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Abstract
For a liquid-crystalline side chain polymer with cyanobiphenyl mesogenic groups and a spacer length of four methylene groups the dielectric properties over a wide frequency range are studied. They are compared with a previously published analogous compound with six spacer groups in order to get the spacer length dependence of dielectric relaxations. Both compounds have been analysed in terms of theoretical relaxation curves. The δ-relaxation is more asymmetrically broadened and shifted to longer relaxation times for shorter spacer. This is consistent with its molecular interpretation as end-to-end rotation around the short molecular axis. The relaxation in perpendicular orientation is strongly shifted to longer relaxation times and shows another temperature dependence for shorter spacer. This behaviour is attributed to superposition of up to three separate relaxation processes.