Theory of Ferroelectric Liquid Crystals

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Abstract
In the ferroelectric helicoidal smectic C* phase the chiral molecules are tilted with their long axes from the normal to smectic layers. The direction of the tilt precesses as one goes from one smectic layer to another resulting in a helicoidal structure. The order parameter of the phase transition from the smectic A to the smectic C* phase is the two component tilt vector, which breaks the axial symmetry around the long molecular axis and induces the ordering of transverse molecular dipoles. The extended thermodynamic model is reviewed, which includes the bilinear as well as the biquadratic coupling between the tilt and the transverse polarization and describes in a unified way the thermodynamic properties of these systems. A microscopic model is introduced, which is consistent with the extended thermodynamic model, and the effect of the shape of molecules on the macroscopic properties of ferroelectric liquid crystals is estimated.