Electro-optical and dielectric characterizations of the Goldstone mode relaxation in ferroelectric chiral smectic C liquid crystals

Linear and non-linear dielectric properties of a short-pitch ferroelectric liquid crystal stabilized by a polymer network

Linear and non-linear dielectric measurements were carried out on a ferroelectric liquid crystal stabilized by an anisotropic polymer network. The polymerization process was achieved at room temperature. It was performed from an achiral monomer in the ferroelectric chiral smectic C phase, exhibiting a very short helical pitch and a large polarization. The linear and non-linear dielectric spectroscopy were also completed by textural morphology as well as structural and ferroelectric characterizations. All these measurements were carried out on a pure ferroelectric liquid crystal material and on composite films containing two polymer concentrations. The increase of the polymer network density leads to a decrease of the dielectric strength determined in the linear and non-linear dielectric spectroscopy. The complementarity between the linear and non-linear dielectric measurements and their confrontation with a theoretical model allowed the simultaneous determination of some physical parameters such as macroscopic polarization, rotational viscosity and twist elastic energy. We also discuss the effect of the polymer network density on the obtained physical parameters.

Second-harmonic dielectric response of an antiferroelectric liquid crystal under dc electric fields

Second-harmonic dielectric response under dc fields in an antiferroelectric liquid-crystal 4-(1-methyl-heptyloxycarbonyl)phenyl 4-octylcarbonyloxybiphenyl- 4-carboxylate (MHPOCBC) has been investigated. The second-harmonic response from the amplitude mode in the smectic- Calpha* phase was observed due to the symmetry breaking by the application of dc electric fields. A Landau theory was developed in order to analyze experimentally obtained frequency dispersions. From the analysis we found a softening of the amplitude mode with increasing the dc field at a temperature close to the smectic- Calpha*-smectic- A phase transition point. It was turned out that the relaxation frequency of the amplitude mode decreases linearly with the applied electric field.