Schlieren textures in smectic liquid crystals

The details of well developed schlieren textures have been observed at smectic C and B modifications. In these textures whole numbered point singularities occur and inversion walls with strong similarities to nematic schlieren textures. It is shown that the occurrence of smectic schlieren textures is due to suppositions derived theoretically by Nehring and Saupe. These suppositions are: tilted structure and plane layers with the layers parallel to the supporting glass slides. In smectic B inversion walls occur which allow to conclude on variable tilt angles of the structure.     

Energy criteria for orientation of smectic C* liquid crystals in electrooptic elements

Energy analysis of the types of orientation of smectic C* liquid crystals is performed. Criteria for the type and quality of their orientation in electrooptic elements with surfaces of orientants of different nature are revealed. An energy parameter of the optical quality of planar orientation of a smectic C* liquid crystal is proposed, which determines the contrast ratio of electrooptic elements independent of the type and nature of the smectic C* liquid crystal and the orientant.     

The Electrohydrodynamical Transient instability region in Smectic C liquid crystals

The hydrodynamical instability transient region between conducting („initial”︁ domains) and dielectric („fundamental”︁ domains) regimes in smectic C is investigated. Two-dimensional domain structure and two-dimensional coherent light diffraction is observed in the transient region. A comparison with electrohydrodynamical instability transient region in nematics is presented.     

Structure and thermal fluctuations in thin films of smectic liquid crystals

Thermal fluctuations of the smectic layers in freely suspended thin liquid crystalline films have been studied by the methods of X-ray diffraction and reflectometry. The fluctuation dynamics is studied by the methods of photon correlation spectroscopy with the use of a source of coherent synchrotron radiation. In freely suspended smectic films, the typical relaxation times are of the order of several microseconds. In thin liquid crystalline films, the simultaneous damped and oscillatory behavior was observed for the layer undulations.     

A special shear method of alignment for smectic liquid crystals

A special shear method is presented for the planar alignment of smectic liquid crystals. The shear was applied at the isotropic-smectic A or cholesteric-smectic A phase transition temperature, when the “batonnets” floated freely in the isotropic or cholesteric fluid. This type of shearing provided good alignment in the broad range of sample thickness (up to 100 μm) with monodomain areas of about one square centimeter.     

Thermo‐morphological properties of the smectic C* mesophase in new chiral salicyaldimine liquid crystals

Specific textures and their temperature transformations in large temperature interval for the chiral smectic C* mesophase of new liquid crystalline materials, synthesized by our group, have been investigated in detail. Temperature dependences of the pitch of helical structure of the smectic C* mesophase have been determined for these materials. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phenomenological model of phase transitions between isotropic, nematic, and smectic phases in liquid crystals

The existence of the biaxial smectic phase SmA _b has been proved in the model of the Landau potential with two (nematic and smectic) interacting order parameters.     

Discontinuous Freedericksz transition in the smectic C phase

The threshold field of the Freedericksz transition in planar oriented S_C monocrystals possessing positive dielectric anisotropy is calculated for two boundary conditions. It is shown that the threshold field is relatively low when a discontinuous transition is taken into consideration. The effective elastic constant is determined from the experimental data.     

Phase transition of nematic to smectic C through an intermediate boundary induced smectic A structure

An intermediate phase has been observed at the transition nematic to smectic C where a smectic A structure induced by the boundaries and a nematic phase exist simultaneously. The temperature interval of existence of the intermediate phase is of the order of one tenth of degree. Several conditions are necessary for its appearance: the latent heat L of the phase transition nematic-smectic C of the liquid crystal should be sufficiently small (L < k_BT_c); the nematic phase should undergo a bend deformation by the boundaries (possibly a twist one as well) and the transition nematic-smectic C should be carried out as slower as possible.     

Thermal and optical studies on induced smectic phases of inter molecular hydrogen bonded liquid crystals between decyloxy benzoic acid and citric acid

Hydrogen bonded liquid crystal complex (HBLC) is prepared from mesogenic 4-decyloxy benzoic acid (10OBA) and aliphatic nonmesogenic citric acid (CA). Liquid crystal (LC) phases are investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) studies. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR) validate the intermolecular complementary, cyclic type of hydrogen bond (HB) and molecular environment in the designed HBLC complex. Mesomorphic phases like nematic, smectic X (Sm X) and smectic G (Sm G) are characterized by various textures and using different techniques such as POM, DSC and optical tilt angle measurements. Thermal span width and thermal stability factor for the observed phase is calculated. The complexes are prepared in different mole ratio and their corresponding influences on the phase transitions are discussed. Also it is observed that the HB units play a vital role in stabilizing the new Sm X phase. The variation in thermal stability of smectic phases due to the influence of aromatic cores and length of end chain in the different mole ratio of the present HBLC complexes are also discussed. The variation of tilt angle with respect to temperature in the smectic phase has been experimentally calculated and analyzed. The lowered melting and clearing transition temperatures and extended thermal span width in the Sm X phase are also reported.     

High-frequency acoustic domains in liquid crystals

A mechanism for the formation of one-and two-dimensional domains in planar nematic and cholesteric liquid crystal samples in an ultrasonic field is discussed. A new approach to the analysis of this phenomenon based on the concepts of nonequilibrium hydrodynamics and taking into account the relaxation properties of the mesophase is experimentally substantiated.     

Measurement of optical biaxiality and tilt angle in A smectic c liquid crystal

We present a new method of measuring the tilt angle and the optical biaxiality in liquid crystals (LCs). The method uses a fitting procedure of the optical path difference in specially prepared LC cells. Measurements are performed in the S_C phase of 4-n-hexyloxyphenyl-4n-decyloxybenzoate (HOPDOB) by means of microscopic observations in a rotary heating stage.