Dielectric Spectroscopy of the Electroclinic Effect in the Ferroelectric Liquid Crystal Materials

We present the dielectric properties of two pure ferroelectric liquid crystal materials (C11 and C12) exhibiting cholesteric (N*), paraelectric smectic A (SmA*), and ferroelectric chiral smectic C (SmC*) phases. In the dielectric measurements carried out without a DC bias field, we studied the soft-mode relaxation in the SmA* phase. From experimental data and using the results of a Landau model, we evaluate the electroclinic coefficient in the SmA* phase. A soft-mode-like mechanism was also observed in the N* phase for a compound with a shorter chain (C11). This relaxation process is not detected for the homolog with a longer chain (C12). The observation of this mechanism is linked to smectic order fluctuations within the N* phase whose amplitude is more enhanced close to the SmC*-SmA*-N* multicritical point.