# Helix-Free Ferroelectric Liquid Crystals: Electro Optics and Possible Applications
## 2 Ferroelectric Liquid Crystals Compositions Used and Their Basic Properties  
The basis of the new FLCs is the same optically active additives used in known FLC and based on derivatives of terphenyl-dicarboxylic acid. The difference is only in the specific compositions of FLCs, which is the object of know-how. In spite of the great difference in the rotational viscosity coefficient \(\gamma_{\varphi}\), which in various compositions changes by practically an order of magnitude (from 0.15 to 1.5 P), and in spite of the manifestation of essentially different optical properties (to be discussed below), the values of the spontaneous polarization \(P_{S}\), the initial tilt angle of molecules in smectic layers \(\Theta_{0}\), and the sequence of phase transitions for all new FLCs differ insignificantly (see Table 1).  
The sequence of phase transitions for these compositions is the following:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compositions** & \(\mathbf{\Theta_{b}}\)**, grad.** & \(\mathbf{P_{s}}\)**, \(\mathbf{n}\)/\(\mathbf{c}\)\(\mathbf{c}\)\(\mathbf{m}^{2}\)** & \(\mathbf{\gamma_{op}}\)**P** \\ \hline HF-32B & 21.7 & 40 & 0.7 \\ \hline HF-32C & 22 & 40 & 1.0 \\ \hline HF-32D & 23 & 42 & 0.15 \\ \hline HF-32E & 22 & 45 & 1.5 \\ \hline HF-32F & 21 & 42 & 0.75 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Investigated helix-free ferroelectric liquid crystals (FLC) compositions.  
Figure 2: Alternation of light and dark bands, illustrating the spatially periodic deformation of smectic layers: (**a**) observed experimentally and (**b**) calculated (see Section 5).  
A deformation occurs at a certain ratio between the values of FLC essential parameters, as follows:
* The rotational viscosity is in the range of 0.3 \(<\gamma_{\varphi}<\) 1.0 P. If it is less, the transition to the shear viscosity \(\gamma_{\psi}\) is not achieved, and the soliton mechanism of reorientation of the FLC director is not realized; if it is more than 1 P, the optical response time increases significantly at higher frequencies, and the transition to the soliton mode is not observed;
* The magnitude of the spontaneous polarization \(P_{S}\) is less than 50 nC/cm\({}^{2}\). If it is greater, the saturation voltage increases, the ferroelectric domains begin to form, and residual light scattering takes place after the electric field is turned off.  
The periodical deformation of smectic layers is responsible for the properties of the novel FLCs indicated above. In fact, the fast electro-optical response with continuous gray scale in a transparent mode, which could be used in display devices, is observed in the FLC compositions with a rather long deformation pitch of more than 3 \(\upmu\)m. For example, for the composition HF32F, the deformation pitch is of 4 \(\upmu\)m. Intensive light scattering in FLC, which could be used in polarization-free devices, manifests in compositions with rather short deformation pitch of 1.5 \(\div\) 2.0 \(\upmu\)m (this value for HF32 is about 1.5 \(\upmu\)m). A fast-changing phase delay (initiated by light scattering switching on), which could be used for suppressing speckles in laser images, is realized more preferably in FLC compositions with a deformation period of about 3 \(\upmu\)m. Although the periods of spatial deformation for HF32F and HF32B are different, other essential parameters of these compositions are almost the same (see Table 1).