Collective fluctuation in chiral smectic phases of main-chain liquid crystalline polymers

We have investigated the collective fluctuation in the chiral smectic phases of main-chain polyesters having a mesogenic p,p'-dibenzoate unit via dielectric and dynamic electrooptical measurements. A relaxation due to the Goldstone mode was observed at several tens of Hz in the chiral smectic C (SmC*) phase in both measurements, where another relaxation associated with the soft mode was also confirmed around the SmA-SmC* phase transition temperature. Although the mesogens are linked together in a main-chain liquid crystalline polymer, the observed soft mode is associated with the tilt fluctuation of the average direction of the mesogens.