A series of novel low molecular weight organosiloxane compounds have been investigated using a number of techniques such as: texture, birefringence measurements and dielectric spectroscopy. Some materials under investigation are shown to have a direct transition to de Vries SmA* phase on cooling from the isotropic phase, whereas the others show first a transition from isotropic to orthogonal SmA*, followed by a transition from orthogonal SmA* to de Vries SmA* phase.

An achiral compound, DIO, known to exhibit three nematic phases namely N, N_X and N_F, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic N_F shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.

Two homologue achiral bent-core liquid crystals (LCs), BCN66 and BCN84, in their nematic phases are studied by dielectric spectroscopy in the frequency range 10 Hz–10 MHz. In each of these compounds, two relaxation processes are identified and assigned to (i) collective dynamics of molecules in nanometer-sized cybotactic clusters and (ii) individual molecular relaxations, in the ascending order of frequency of the probe field. The temperature and the bias electric field dependence of the dielectric strength and relaxation frequency for these processes are shown to give rise to sharpness in cluster boundaries, increased size and volume fraction in the LC nematic phase. The effect of the bias field on the LC cell is similar to reducing its temperature; both variables increase the cluster size and volume fraction and give rise to sharp cluster boundaries. The findings confirm that dielectric spectroscopy is a powerful and an extremely useful technique to provide a deeper understanding of the mechanism of cybotactic cluster formation in the isotropic liquid and the nematic phase of LCs as a function of temperature and the bias field.

We report on the observation of an electro-optical effect for a linear rotation of the optical axis as a function of the electric field in a tilted liquid crystalline smectic phase of an achiral bent-core compound, attributed to a spontaneous helical state in its SmC _S P _F phase.

The fundamental parameter of the uniaxial liquid crystalline state that governs nearly all of its physical properties is the primary orientational order parameter ($S$) for the long axes of molecules with respect to the director. The biaxial liquid crystals (LCs) possess biaxial order parameters depending on the phase symmetry of the system. In this paper we show that in the first approximation a biaxial orthogonal smectic phase can be described by two primary order parameters: $S$ for the long axes and $C$ for the ordering of the short axes of molecules. The temperature dependencies of $S$ and $C$ are obtained by the Haller's extrapolation technique through measurements of the optical birefringence and biaxiality on a nontilted polar antiferroelectric (Sm-$A{P}_A$) phase of a homologous series of LCs built from the bent-core achiral molecules. For such a biaxial smectic phase both $S$ and $C$, particularly the temperature dependency of the latter, are being experimentally determined. Results show that $S$ in the orthogonal smectic phase composed of bent cores is higher than in Sm-$A$ calamatic LCs and $C$ is also significantly large.

The authors study the effect of the spontaneous polarization $\left(P_S\right)$ of a ferroelectric liquid crystal mixture with compensated helix and of the thickness of the alignment layer $\left(d_a\right)$ on the analog switching in a cell. The quality of analog switching is established in terms of its contrast ratio, texture in the dark state, and the electrostatic energy. The latter approximates to $P_S^2{d}_a$ for $d_a⪡d$ (thickness of the ferroelectric liquid crystal cell layer).