We have studied the effect of an anisotropic polymer network on the coupling of molecular tilt to applied electric field in the chiral S{A} phase. The polymer network is formed from a photoreactive achiral monomer in a thin planar S{C}{*} cell. Experimental data, obtained from electro-optical measurements near to the S{A}-S{c}{*} transition temperature, T{c} , of the induced molecular tilt, switching time, as well as induced polarization as a function of temperature and electric field strength are presented. The results clearly show that, close to T{c} , the electroclinic effect is largely controlled by the polymer network. The experimental results are discussed in the framework of a simple phenomenological model, extended from the Landau model, which includes the bulk free energy arising from the anisotropic interaction between the polymer network and the liquid crystal director, and the elastic free energy resulting from the anchoring (supposed rigid) of the liquid crystal molecules at the polymer boundaries.

We report the effect of an anisotropic polymer network formed from an achiral photoreactive monomer in a short-pitch chiral SmC* phase on the distortion and the unwinding of the helical structure of the ferroelectric phase. The electro-optical behaviour and ferroelectric properties were experimentally determined for films containing various polymer concentrations. The critical field, E(u), for the transition from the distorted structure to the homogeneous state was measured as a function of polymer concentration. A linear increase of E(u) versus polymer concentration was observed, showing that the helical structure of the short-pitch SmC* phase was stabilized by the polymer network. This behaviour was expected to be a consequence of the increase of the apparent elastic constants of the ferroelectric liquid crystal stabilized by the anisotropic polymer network films. The polymer network morphology was investigated using atomic-force microscopy, revealing a twisted structure of the polymer fibers. This twisted structure was transferred onto a polymer network during the polymerization process within a short-pitch SmC* phase. The increase of the apparent elasticity can then be interpreted by a strong interaction between polymer network and the liquid-crystal molecules. From our experimental data, the coupling coefficient, W(p), characterizing this interaction was evaluated for all studied polymer concentrations.

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.