Collective and Molecular Dynamics in Ferroelectric Liquid Crystals: From Low Molar to Polymeric and Elastomeric Compounds
Broadband dielectric spectroscopy (10−2Hz – 1010Hz) is employed to analyse the collective and molecular dynamics in low molar weight and polymeric ferroelectric liquid crystals (FLC). Below 106Hz two collective dielectric relaxation processes are observed having the character of a soft — mode and that of a Goldstone — mode. The soft — mode is assigned to fluctuations of the amplitude of the helical superstructure, while the Goldstone — mode corresponds to fluctuations of the phase of the ferroelectric helix. In the frequency range between 106Hz and 1010Hz one dielectric relaxation process is observed, the β — relaxation, which is assigned to the libration (hindered rotation) of the mesogenes around their long molecular axis. At the phase transition smectic A / smectic C* this process does not show any deviations from an Arrhenius — like temperature dependence. In comparing low molecular mass and the polymeric side group FLC, the collective and molecular dynamics is found to be qualitatively similar. This open new possible applications for FLC as sensors, actuators or (polymeric) flexible displays.
KeywordsDielectric Loss Soft Mode Bias Field Molecular Axis Dielectric Strength
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