A state of matter in which molecules show a long-range orientational order and no positional order is called a nematic liquid crystal. The best known and most widely used (for example, in modern displays) is the uniaxial nematic, with the rod-like molecules aligned along a single axis, called the director. When the molecules are chiral, the director twists in space, drawing a right-angle helicoid and remaining perpendicular to the helix axis; the structure is called a chiral nematic. Here using transmission electron and optical microscopy, we experimentally demonstrate a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend. The oblique helicoids have a nanoscale pitch. The new twist-bend nematic represents a structural link between the uniaxial nematic (no tilt) and a chiral nematic (helicoids with right-angle tilt).

Hydrocarbon linked mesogenic dimers are found to exhibit an additional nematic phase below the conventional uniaxial nematic phase as confirmed by x-ray diffraction. The phase produces unusual periodic stripe domains in planar cells. The stripes are found to be parallel to the rubbing direction (in rubbed cells) with a well-defined period equal to double the cell gap. The stripes appear without external electromagnetic field, temperature or thickness gradients, rubbing or hybrid alignment treatments. Simple modeling proposes a negative sign for at least one of the two elastic constants: splay and twist, as a necessary condition for the observed pattern.

Infrared absorbance measurements have been carried out on two liquid crystalline organo-siloxane tetrapodes. Results unambiguously show the existence of a biaxial nematic phase below a uniaxial nematic phase. The three components of IR absorbance are used to calculate the various order parameters. On cooling, a weak first-order transition from isotropic to nematic is observed, followed by a second-order phase transition to biaxial nematic where the biaxiality parameters are found to be significantly large. Results are supported by observations from conoscopy and texture. Temperature dependences of the order parameters are well explained by the mean-field model for a biaxial phase.

Some hydrocarbon linked mesogenic dimers are known to exhibit an additional nematic phase (N_x) below a conventional uniaxial nematic (N_u) phase. Although composed of non-chiral molecules, the N_x phase is found to exhibit linear (polar) switching under applied electric field. This switching has remarkably low response time of the order of a few microseconds. Two chiral domains with opposite handedness and consequently opposite responses are found in planar cells. Uniformly lying helix, electroclinic, and flexoelectric effects are given as possible causes for this intriguing phenomenon.

Wide band dielectric and electro-optic spectroscopy of an antiferroelectric liquid crystal (AFLC) has been carried out over a range of frequencies from 1 kHz to 1 GHz. The AFLC sample under investigation possesses a variety of different ferri-, ferro-, and antiferro-electric phases. Dielectric spectroscopy of the LC cells in the antiferroelectric phases reveals both collective and individual dynamics of molecules. In the antiferroelectric SmCA phase, three dielectric relaxation processes are found in the absence of the bias and an additional relaxation process appears under the bias field. A solution of the dynamical equation of the director subject to a weak alternating field for the anitferroelectric helix has been found. A comparison of the results of electro-optic and dielectric spectroscopy with a theoretical study enables a determination of the origin of the relaxation processes in antiferroelectric phases. The mechanism for the distortion of the antiferroelectric helix has been determined using dielectric spectroscopy and a non-linear electro-optic technique.