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We report the influence of the polymer network density formed in short-pitch ferroelectric liquid crystal (FLC) on the soft and the Goldstone dielectric relaxation modes. The experimental results of the pure FLC and the FLC stabilized by a polymer network with various densities are presented and compared. These results reveal that in the SmC;{ *} phase, when the polymer concentration increases, the Goldstone dielectric strength gradually decreases and the relaxation frequency is shifted to higher values. In the SmA;{ *} phase, the results show that close to the SmC;{ *}-SmA;{ *} transition temperature, T_{c} , the soft relaxation mode is largely influenced by the polymer network: a sharp decrease in the dielectric strength and an increase in the relaxation frequency when the polymer density increases were observed. The soft mode is relatively weakly affected by the network for higher temperatures (T> or =T_{c}+0.5 degrees C) . This indicates that the behavior of the soft mode for this temperature domain is dominated rather by thermal effects than by the network. A simple phenomenological approach was proposed to explain the behavior of the soft-mode dielectric strength versus polymer concentration. This model takes into account the anisotropic interaction between the polymer network and the liquid crystal, and the elastic interaction resulting from the anchoring of the liquid crystal molecules at the polymer surfaces. The experimental results are in agreement with the proposed model.

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Chiral liquid crystal material (C12 homologue of biphenyl benzoate series) exhibiting the cholesteric (N*), smectic A (SmA) and ferroelectric smectic C (SmC*) phases have been studied by structural, thermodynamic, electrooptical and dielectric investigations. The helical pitch, tilt angle and spontaneous polarization have been determined. In the dielectric measurements, we have studied the soft mode in the SmC* and SmA phases. From experimental data, we have evaluated the soft-mode rotational viscosity and the electroclinic coefficient in the SmA phase. All results are discussed and compared with previous studies performed on other homologues of the same series. The main result is that the relaxation process detected in the N* phase for the C8, C10 and C11 homologues and explained as a soft-mode-like mechanism, is not observed for C12. This corroborates the idea that this mechanism is related to the appearance of smectic order fluctuations within N* phase, the amplitude of which is increased when approaching the SmC*-SmA-N* multicritical point.