Effect of the network density on dynamics of the soft and the Goldstone modes in short-pitch ferroelectric liquid crystals stabilized by an anisotropic polymer network.

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.