The effects of sequential change of trans-cyclohexane in three-ring and four-ring molecules on their thermal behavior and the phase transition, threshold voltage (Vth), birefringence (Δn) of their mixtures were investigated. The structure with alternate phenyl and cyclohexane go against the stability of the mesomorphic phase, but favor to the decrease of Vth and Δn.

Three new series of cubane-1,4-dicarboxylic acid derivatives have been prepared as bis[(4'-alkyl)phenyl]cubane-1,4-dicarboxylates, bis[(4'-alkoxy)phenyl]cubane-1,4-dicarboxylates, and two chiral derivatives as bis(cholestenyl)cubane-1,4-dicarboxylate and (S)- bis{4'-[(2-methylbutyl)oxycarbonyl}phenyl}cubane-1,4-dicarboxylate. These ester type compounds have the bulky cubane skeleton as a central building block in their core system. The lower homologues of the alkoxyphenyl ester series exhibited nematic, the higher ones smectic A phase. The mesophase formation was supressed in case of the (4-alkyl)phenyl- and chiral derivatives.

New series of chiral liquid crystalline materials with the same rigid core with keto group and a various number of (S)-lactate groups in the chiral part of the moelcule have been studid by DSC, X-ray, electro-optics and dielectric spectroscopy. All compounds contain branched terminal alkyl chain derived from (S)-2-methylbutanol. The influence of the lactate number on mesogenic behavior of those compounds has been studied. All compounds show the paraelectric SmA phase and the ferroelectric SmC* phase in a rather wide temperature range. The antiferroelectric SmC*_A phase was detected for the compound possessing two lactate groups. A polar field-induced smectic phase have been observed by electro-optic studies.

We report the synthesis procedures, phase transition temperatures, optical and dielectric properties of the fluoro and chloro -- substituted two rings and three rings isothiocyanatotolanes. Three eutectic mixtures comprising of these isothiocyanatotolane compounds showing a wide nematic range, low viscosity and high birefringence (~0.4) are formulated.

A series of new liquid crystalline cyclic siloxane oligomers was prepared to investigate the influence of the long alkyl chain as an end substituent on their mesomorphic behaviour. Liquid crystalline properties of the new cyclosiloxanes were examined by DSC, polarized optical microscopy and X-ray diffraction methods.

A series of novel ester imides and thioimides have been synthesized from N-substituted trimellitimides and 4-hydroxybiphenyl or 4'-alkoxy-4-hydroxybiphenyls. The correlation between structure and behavior of the obtained compounds was studied. It has been found that imides without alkoxy tails are nonliquid crystalline while compounds possessing 4'-O-substituted biphenol moieties exhibit smectic phases. An introduction of sulfur atoms into an imide ring instead of oxygen atoms resulted in the fact that appropriate thioimides show monotropic SmA phases while the parent imides were nonliquid crystalline. Compounds with short aliphatic substituents (C₁ - C₄) show only SmA phases. The longer tails (C₅) induce also SmC phases.

The novel banana-shaped liquid crystal materials namely 4-methyl-1,3-benzenedicarbonic acid esters have been synthesized and their mesomorphic properties have been studied. The differential scanning calorimeter investigation showed that these compounds decomposed at temperature above 200°C, so the thermograph measurements in regime of cooling from isotropic liquid have not made. Data of polarizing microscopy show that all prepared compounds are mesomorphic and form mesophase in narrow temperature interval, which have not identified.

Our investigation purpose is the determination of the molecular structure peculiarity of banana-shaped compounds, which promotes the formation "banana" phase or prevents from it. The homologous series of the 4-methoxy-1,3-benzene-dicarbonic acid esters have been synthesized and their mesogenic properties have been studied. On the basis of the polarization microscope it is shown that compounds containing 5,6 or 12 carbon atoms in the lateral alkyl chain are non-mesomorphic. But compounds with 7 - 9 carbonic atoms in the lateral alkyl chain form smectic phase. On the base of differential scanning calorimeter measurement and X-ray diffraction investigation this phase may be preliminary attributed to "banana"-smectic phase, we kind of which we have not identified.

The synthesis and investigation of mesomorphic properties of 5,10,15,20-tetra(aminophenyl)porphin derivatives on the basis of 3,4,5-trihydroxybezoic acid were carried out to study the influence of molecular structure geometry on thermotropic and lyotropic mesomorphism in a number of organic solvents. Introduction of two bulky fragments into R₁ position (X, XI) or four bulky fragments into R₁ and R₂ (XII, XIII) positions (in case of meta- or ortho-substitution of benzene rings) leads to emerging of monotropic mesophase. Tetra-substitution of porphyrine cycle in the para-position of the benzene ring (compound XIV) reveals the enantiotropic mesophase. The influence of bulky fragments on the glass-forming capacity of the compounds was researched.

A connection between chirality at the molecular and mesoscopic scales and the corresponding macroscopic chiral structure of liquid crystalline phases is one of key issues of soft matter research. The most appropriate theoretical tools to study chirality-induced structures are statistical field theory of correlation functions and computer simulations. The correlations are calculated for the order parameter fields that enter phenomenological description of a given chiral phase, like two-point correlations for cholesterics as constructed out of the alignment tensor field. A quantity that could subsequently be derived from such correlations and used to measure chirality is, for example, the optical activity tensor or, as for bent-core systems, the traceless and symmetric third-rank tensor. In this paper we explicitly show a relation between chirality and two-point correlations of the alignment tensor field. The correlations are determined from Monte-Carlo simulations for a model isotropic liquid of chiral Gay-Berne fluid. The calculated molecular quantities are consistent with recent predictions of statistical field theory.

Dielectric spectroscopy of the ferro- and antiferro-electric phases of an antiferroelectric liquid crystal namely [4,4-(1-methyloctyloxycarbonyl)phenyl]-4'-[3-(butanoiloxy)prop-1-oxy]biphenyl carboxylate (MOPB(H)PBC) has been carried out in the frequency range of 1 Hz to 10 MHz. Typical behavior of soft mode relaxation in SmA* has been observed. Two-dielectric relaxation modes: FM1 (Ferroelectric mode 1) and FM2 (Ferroelectric mode 2) have been recognized in SmC* phase. The relaxation frequencies for FM1 lie between 2 and 25 Hz and those for FM2 lie around 3.5 kHz (Goldstone mode). Also two dielectric relaxation modes AFM1 (Antiferroelectric mode 1) and AFM2 (Antiferroelectric mode 2) have been observed in antiferroelectric SmC_A* phase. AFM1 lies between 3 and 10 kHz and its relaxation frequency decreases with decrease in temperature. AFM2 lies above 400 kHz but the temperature dependence of its realization frequency is opposite to that of AFM1.

Tristate regular mixtures with different electro-optical properties such as threshold voltage, saturation voltage, holding ratio and response time are presented. The relation of properties with the structure of compounds is discussed. All of mixtures show only moderate dynamic and static contrast but big gray level scale without hysteresis for positive and negative field driving.

Mesomorphic properties (phase transitions enthalpies and temperatures) and the dependence of smectic layer spacings upon reduced temperature for eight homologous series of three ring ester such as: (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl or (S)-(+)-4-(1-methylheptyloxycarbonyl)-3-fluorophenyl or (S)-(+)-4-(1-methyl-heptyloxycarbonyl)-2-fluorophenyl 4'-(perfluoroalkanoyloxyhexyloxy)biphenylates and 4'-(alkanoyloxyhexyloxy)-biphenylates, and (S)-(+)-4-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4'-(perfluoroalkanoyloxyhexyloxy)benzoates and 4'-(alkanoyloxyhexyloxy)benzoates were described. The terminal chain fluorinated compounds have SmC*_anti-SmC*-SmA-Iso phase sequence and a high tilted (orthoconic) antiferroelectric phase in broad temperature range.

Bi- and multicomponent mixtures consisted of two groups of synclinic chiral esters: first one with a partially fluorinated terminal chain and the second one with hydrogenated terminal chain have been used for investigations. For some systems the induction of the anticlinic smectic C_A* phase was observed. Enthalpies of the phase transitions for the systems with induced smectic C_A phase upon compositions and specific heat were measured by DSC method.

The molecular dynamics of a recently synthesized chiral antiferroelectric liquid crystal (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl-4'-(3-butanoiloxyprop-1-oxy)biphenyl-4'-carboxylate (in short MHPB(H)PBC) exhibiting SmA* and SmC_A* phases have been studied in the frequency range of 1 Hz to 10 MHz. In the SmA* phase only one doubly degenerate soft mode relaxation exists which becomes critical at transition temperature and its splits into two modes in SmC_A* phase, one at high frequency about 500 kHz, the other at low frequency about 40 kHz. Relaxation frequencies of both modes decrease slowly with decrease in temperature. These two observed modes are due to the anti-phase and in-phase azimuthal angle fluctuations of the molecules in the anti-tilt pairs. The temperature dependence of the dielectric strengths and relaxation frequencies, determined by Cole-Cole plot clearly reveals that SmA* to SmC_A* transition is weakly first order.

The convenient synthesis method and mesomorphic properties of novel liquid crystalline homologous series of the chiral thiobenzoate in which the chiral branched chain (S)-(1-methylheptyloxy) was attached to the biphenyl have been presented. They are liquid crystals compounds of the general formula MHOBSn (S)-(+)-4-(1-methylheptyloxy)-biphenyl-(4'-alkylphenyl)-thiobenzoate, where n denotes number of carbon atoms in the alkyl chain). DSC and polarization microscopy and X-ray diffraction measurements shoved that (S)-MHOBSn possess a rich phase polymorphism: two high ordered tilted smectic phases SmG* and SmI* as well as ferroelectric smectic C, SmC* and chiral nematic phase (N*). All compounds containing stabile enantiotropic SmC* and N* phases. The influence of chemical purity of final compound on phase behavior has been studied. The existence of weak intermolecular hydrogen bonds of (S)-MHOBSn was confirmed by FTIR method.

Rotational potential of molecule in smectic phases, introduced by Zeks, includes two important parts: dipolar as well as quadrupolar ones. The first part is valid for chiral molecules only, whereas the second one is important for chiral and achiral molecules. The question arises: "Whether shape of rotational potential changes when the phase transition between SmC* and SmC_A* appears?" In our opinion, close to the temperature of phase transition (FLC-AFLC) magnitudes of both, dipolar and quadrupolar parts change. Quadrupolar coupling is more important for antiferroelectric phase, while dipolar factor overwhelms quadrupolar one, for ferroelectric phase.

Recently the investigation in the field of LCD technology has been boosted by the availability of new materials. The new group of fluorinated mesogens has been recently synthesized in Poland. In this work we have been focused on investigations of properties of materials having the broad temperature range of antiferroelectric phase. Such key factors as apparent tilt angle and structural properties and electro-optical performance have been studied by means of electro-optical and X-ray methods. The bend molecular shape and the presence of fluorinated tail has been assumed as a factor leading to an extremely high apparent optical tilt. The length of the fluorinated chain seems to affect th mesogenic behavior.

Precise measurements of physical macroscopic properties such as temperature dependencies of the spontaneous polarization, the tilt angle and the electric permittivity were performed (S)-4-(1-methyloctyloxycarbonyl)phenyl 4-octyloxybiphenyl-4'-carboxylate and their mixtures. Some of these results as well as the results of DSC and X-ray studies were presented by us earlier. On based above and calculations of molecular structure of investigated compounds the aim of this work was to explain the ability for induction an anticlinic SmC_A phase in bicomponent mixtures composed of these.

In the mixtures of chiral compounds in which smectic A phase exists in limited range of concentration the selective reflection of light for compositions without smectic A phase can be from red to blue the same as above smectic phase or from blue to red as in mixtures without smectic phase. To check either the type of smectic A phase of the phenomenon of phase induction are responsible for the difference in the light colour sequence polar compounds having chiral nematic phase were mixed with compounds having nonpolar ('classic') smectic A phase or polar A₁ or A_d smectic phases in lower temperatures than chiral nematic phase (in these systems the smectic phase was destabilized) or with compounds having nematic phase chosen in such a way that smectic A₁ or A_d were induced in the system. It was found that the light colour sequence depends on the distance of compositions giving the selective reflection of the light in temperature-concentration scale from smectic phase.

In the mixture of two nonpolar compounds with the destabilization of smectic A phase the selective reflection of the light is from red to blue with increasing temperature and in the mixture of two polar compounds with the induction of smectic A_d phase the selective reflection of the light is from blue to red with increasing temperature. To check if the polarity of compounds are responsible for the differens in colour changes of the selectively reflected light two nonpolar, two polar, and polar and nonpolar compounds were mix together. It was found that the polarity of compounds do not influence the colour sequence only the distance of the compositions giving selective reflection of the light in the temperature-concentration scale from smectic phase.

Recently synthesized in Institute of Chemistry, Military University of Technology (Warsaw), antiferroelectric liquid crystal compound (MHPOPOPC) has been studied by means of low frequency dielectric spectroscopy. This compound shows very broad temperature range of ferrielectric subphases: the SmC*_α, the SmC*_β, and the SmC*_γ in cooling process. The dielectric characteristic of these subphases are presented. In the SmC*_α phase only soft mode was observed which suggest the antiferroelectric nature of this subphase in the investigated compound. In the SmC*_β, phase relaxation process of characteristic antiferroelectric ordering was observed. In the SmC*_γ ferrielectric Goldstone mode was registered. The temperature dependence of parameter of these modes were presented.

Molecular theory of the ferroelectric and antiferroelectric smectic phases is developed taking into account the distribution of dipole moment in molecule of liquid crystal. Very important role are played mutual dislocation different fragments molecules inside smectic layer and play key role in dipole-dipole interaction between neighboring layers. Microscopic theory is constructed using the dipole-dipole interaction of the permanent molecular dipole moments. Three ordered phases are found, one has synclinic, second is anticlinic and third is twisted structure. In twisted structure the angle between two layers is 90 degree. Discuss specific ordering which is necessary for formation every phase.

We report measurements of the temperature dependences of the birefringence of a number of nematogens under high pressures. In a compound whose molecules have large longitudinal dipole moments, we detect a nematic to nematic transition when the order parameter is sufficiently high. We also describe a technique of subjecting aligned liquid crystal droplets to large negative pressures and measuring the temperature dependence of birefringence under isochoric conditions. The temperature range of the partial bilayer smectic A_d phase gets shrunk at elevated pressures but gets enlarged under tension.

Results of dielectric studies (static and dynamic) carried out on several new synthesized substances (in most cases the tolane derivatives) are presented. Apart from pure substances the mixtures of two or more components were also studied. The dielectric properties: tensor components of the permittivity, the dielectric anisotropy, low and high frequency relaxation times are analyzed in view of dipole structures of molecules and the liquid crystalline phases occurred.

Several linearly conjugated isothiocyanato (NCS) tolanes, biphenyl-tolanes and bistolanes were synthesized and their properties evaluated. Eutectic mixtures compromising these compounds were formulated. The temperature dependent birefringence, visco-elastic coefficient and figure-of-merit were measured. These isothiocyanato tolane mixtures exhibit a favorably high figure of merit at elevated temperatures. Potential applications of these mixtures for laser beam steering, tunable-focus lens and telecom variable optical attenuator are emphasized.

Density functional theory (DFT) calculations for 6020CB cyano biphenyl derivative were performed (using StoBe code). Total energy was calculated for different possible conformations of the rod-like molecule and the optimal conformation was found for the terminal chain lying in the plane of attached phenyl ring, whereas the rings of biphenyl were twisted ca. 35°. The calculation of molecular geometry with removal of restrictions for all atoms changed rod-like shape of molecule towards banana-like with the angle between axes of phenyl rings and chain ca. 150°. Electron densities for the lowest energy conformations were studied showing the decay of electron cloud at 2 Å. Finally the interactions of two molecules both rod-like and banana-like were also analyzed for different positions of rigid cores vs. terminal chains. Minimum energy criterion was used for each geometry of the system. It was found that rod-like conformations has reached the lowest energy for slightly shifted position of molecules whereas banana-like were packed close together. Many conformations with similar energies may give some hints towards interpretation of rich polymorphism of 6020CB which has been observed experimentally.

Recently photonic crystals with a three-dimensional ordered structure with periodicity of the optical wavelength have attracted attention from both fundamental and practical points of view. The physics and applications of photonic crystals have been active topic of research now. The application of photonic crystals is to create tunable band gap materials especially in visible spectra region, where the gap could be controlled by an external parameter. We have studied transmission and linear dichroism spectra of synthetic opal, refractive index n = 1,342, infiltrated with nematic liquid crystal with averaged refractive index n = 1,596 or with water n = 1,30 and alcohol n = 1,28. We demonstrating that the position of the stop band in the visible spectra is shifted by changing of refractive index of the infiltrated material or by changing the filling factor or by variation of an incidence angle of light.

Temperature driven first order transition from isotropic to nematic phase in liquid crystals with and without random and quenched orientational disorder is investigated employing multicanonical Monte Carlo simulation. A lattice model with periodic boundary conditions is employed with the pair wise interaction of two nearest neighbor liquid crystal molecules given by the Lebwohl-Lasher potential. The transition temperature decreases with increase of disorder; also the transition appears to soften under strong disorder.

Bistable director configurations are of great interest in liquid crystal display technologies, offering the possibility of higher resolution combined with reduced power consumption. One way to achieve such bistability is to use the cell geometry. As part of an ongoing programme to analyze quasi-stable configurations of liquid crystals in polyhedral geometries, we construct a topological classification scheme of unit-vector fields in convex polyhedra subject to tangential boundary conditions and obtain a general lower bound on the energy of these configurations. We also study the specific case of a unit cube, where we obtain lower and upper bounds for the energies of a family of topological types.

Elastic deformations of nematic liquid crystal layers subjected to d.c. electric field were studied numerically. Nearly planar alignment with 1° tilt angle and with finite surface anchoring strength was assumed. The flexoelectric properties of the nematic material as well as the ionic space charge were taken into account. Perfectly blocking electrodes were adopted. The director orientation, the electric potential distribution and the space charge density were calculated. The optical transmission of the layer placed between crossed polarizers was also determined. The deformations had nearly threshold character due to the low value of the surface tilt. It was found that the threshold voltage strongly depended on the parameters of the system. When the nematic was not flexoelectric, the value of the threshold voltage was independent of the ion concentration and was equal to about 1 volt. In the case of a flexoelectric nematic, the threshold as low as a few tenths of a volt occurred when the ion concentration was sufficiently high, and given sufficiently large magnitudes of the flexoelectric coefficients. These results can be explained as the effect of the inhomogeneous electric field arising in vicinity of the surfaces created by the ionic space charge redistributed by the external voltage.

Langmuir and Langmuir-Blodgett films of various dyes, namely derivatives of: 3,4,9,10-perylenetetracarboxylic acid, 3,4,9-perylenetricarboxylic acid, naphthalenebicarboxylic acid and naphthoylenebenzimidazole as well as of their mixtures with a liquid crystal were investigated. The dependence of the surface pressure -- on the mean molecular area for Langmuir films was measured, from which the molecular organization and the miscibility of components in the monomolecular layer at the air-water interface were determined. For Langmuir-Blodgett films the absorption and emission spectra were recorded and information about the spectral properties and molecular alignment of dyes and liquid crystals in ultrathin layers at solid substrates was obtained.

The orientational behavior of some liquid crystals with various molecular structure was studied by means of classical methods of optical spectroscopy: absorption of the polarized light in the visible region, fluorescence depolarization and Raman scattering depolarization. The dichroic dye dimethylamino-nitrostilbene was added to liquid crystals and acted as guest probe reflecting the host orientation in absorption and fluorescence measurements. The absorption, emission and Raman scattering spectra of the linearly polarized light were recorded as a function of temperature in the nematic phase. On the basis of these spectra the order parameters <P₂> and <P₄> as well as the molecular distribution function were determined. It was found that the molecular structure of liquid crystals affects the orientational order of molecules. Moreover, the effect of the dye presence on the orienting properties of liquid crystalline hosts was discussed.

Proton Magnetic relaxation dispersion (PMRD) measurements were made, at several temperatures, in the nematic phase of the liquid crystal 80CB employing field cycling NMR technique. PMRD data show that pretransitional effects dominate the relaxation mechanism within about two degrees from the isotropic -- nematic transition temperature. The nematic director fluctuations essentially determine the relaxation mechanism at lower temperatures. The presence of short range smectic organizations, and a rapid increase in the size of these clusters at the nematic-smectic transition, could be observed through these PMRD studies. While in the mid-nematic phase these clusters are relatively smaller and isotropic in shape, their size grows by more than an order of magnitude and they become anisotropic in shape as nematic -- smectic transition is approached. The information regarding the other dynamic processes, such as molecular self-diffusion and reorientations, which also contribute to the spin relaxation, is also obtained through these studies.

The influence of the wavelength of light on values of polarisability tensor components α_parallel, α_{perpendicular}, polarisability anisotropy (α_parallel - α_{perpendicular}) and the order parameter S of liquid crystal molecules was verified. The refractive indices are functions of temperature and light wavelength. The values α_parallel and α_{perpendicular} of a liquid crystal molecule can be calculated from refractive indices, density, and coefficient in the Valentova equation. Here, it was found that there is a relation between the wavelengths of the light and values of (α_parallel - α_{perpendicular}) and α_parallel, α_{perpendicular} of p-(p-ethoxyphenylazo)phenyl heptanoate molecule. The values of the order parameter S obtained for the studied material are identical for all wavlengths of light.

The creation reasons of liquid crystal state have not explained up to now. This article is devoted for the elaboration a new solution of this problem. Author found the new calculation method of expression Σ(r_i)² which is a function of temperature, molecular weight and light wavelength. The Σ(r_i)² characterize the molecule of liquid and is connected with the distance polarizability tensor components α_parallel1, α_{perpendicular1} by the formula. Σ(r_i)² = (Z r_o)^½ [(α_parallel1)^½/2 + (α_{perpendicular1})^½]. For liquid crystal one can obtain two values of Σ(r_i)². First the Σ(r_i)²_To for the transition temperature T_o the isotropic liquid state of liquid crystal and second Σ(r_i)²_Tc for the transition temperature to the solid state of liquid Crystal. These quantities must to satisfy the relation Σ(r_i)²_To < Σ(r_i)²_Tc for all liquid crystals. If it is inversely the liquid does not possess the liquid crystal properties.

AFM studies of mixtures with different smectic A, B and E phase were done. Compounds with terminal NCS group were used. AFM images were obtained for liquid crystals samples spread on mica surface or mica covered by polyvinyl alcohol in order to examine the influence of molecular orientation.

Three wedge cells of the wedge angle of order of few milliradians were used to measure the phase shift between ordinary and extraordinary ray of transmitted light, for the stationary states, induced by magnetic or electric field. A nematic liquid crystal PCB, filling the cell, was of the planar alignment enforced by the previous treatment of the flat boundary plates. Two polyimides, MP9 and PM2, and clean glass were used as aligning substances. A system of interference fringes appeared in each cell placed in normally incident light between analyzer and polarizer crossed. In the neighborhood of each fringe a cell was considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness. The dependence of the phase shift on applied external fields was measured for twenty-six interference fringes. The nematic liquid crystal material parameters (the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility and the boundary tilt angle as a function of torque) were determined by comparing the calculated characteristics to the measured ones i.e. by solving the inverse problem simultaneously for all measured characteristics as input data. Each of studied cells represented distinct case of anchoring: strong, medium or weak.

A wedge cell of the wedge angle of order of few milliradians was used to measure threshold magnetic fields for the magnetic Freedericksz transition. A nematic liquid crystal filling the cell was of planar orientation enforced by the treatment of the flat boundary plates. A system of interference fringes appeared in the cell placed in normally incident light between analyzer and polarizer crossed. In the vicinity of each fringe the cell could be considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness. The threshold magnetic field magnitudes were interpreted as eigenvalues of the boundary eigenvalue problem for the operator of second derivative; the interaction between the nematics and the substrate was described by the Rapini-Papoular formula (i.e. weak coupling was considered). The resulting formulae were used to determine the polar anchoring energy coefficient and the anisotropy of diamagnetic susceptibility after the threshold fields measured. The method was applied to characterize the nematic liquid crystal PCB and the coupling between it and the substrates made of poly(amic acid) MP2. The estimates of material parameters agreed pretty well with those determined by the composite method.

Wedge cells of the wedge angle of order of few milliradians were used to measure the threshold voltages for the Freedericksz transition in electric and magnetic fields crossed. A nematic liquid crystal, PCB, filling cells was of planar orientation enforced by the treatment of the flat boundary plates, covered with poly(amic acid) PM9. A system of interference fringes appeared in each cell placed in normally incident light between analyzer and polarizer crossed. In the vicinity of each fringe a cell could be considered as a flat-parallel one and hence it was equivalent to the system of flat cells of different precisely determined thickness. Threshold voltages, parameterized by magnetic field magnitudes were interpreted as the eigenvalues of the boundary eigenvalue problem for the operator of the second derivative; the interaction between the nematics and the substrates was assumed very strong with the anchoring direction parallel to the cell boundaries. The resulting formulae were used to determine the anisotropy of diamagnetic susceptibility and the splay elastic constant of PCB after the threshold magnitudes measured. The estimates of material parameters agreed well with those determined by the composite method.

Octyl and decyl members of the homologous series 4(4'-n-Alkoxybenzoyloxy)phenyl azo-4"-isoamyloxy benzene have been studied by optical microscopy, DSC and X-ray diffraction techniques. Transition temperatures of the compounds are determined by observing texture by a polarizing microscope while transition enthalpies and entropies are determined by DSC studies. X-ray diffraction photographs of magnetically aligned samples indicate that the octyl member has cybotactic nematic phase while decyl member has cybotactic nematic and monotropic smectic A phase. X-ray photographs are analyzed to calculate intermolecular distance, apparent molecular length in nematics, layer spacing in smectics and orientational order parameters (<P₂> and <P₄>). Temperature dependence of these parameters has been discussed. Values of <P₂> and <P₄> are found to be consistent with Maier-Soupe theoretical values. Lengths of the molecules (L) in most extended conformation are found to be greater than the apparent molecular lengths in nematic phase which suggest that the molecules are tilted in the plane of cybotactic groups. Calculated tilt angles are found to be in between 41.8° to 43.3°.

We perform a numerical study of the annihilation of nematic radial and hyperbolic point defect. Both the pre-collision and post-collision stages are taken into account. Initially a pair of defects is induced at the axis of the cylindrical capillary. A semi-microscopic interaction potential and the Brownian molecular dynamics are used. In the early stage the cores of defects are negligibly mutually influenced. Their relative velocity is inversely proportional to the separation d between defects. As d becomes comparable to the nematic correlation length, the cores significantly deform. During the collision the defects merge and become indistinguishable. In the post-collision regime the order parameter at the collision site gradually recovers the equilibrium configuration.

The structural transitions in thermotropic ferronematic, i.e. nematic liquid crystal (8CB) doped with fine magnetic particles (d~10 nm), exposed to combined electric and magnetic fields, were studied within the Burylov and Raikher's theory. Using the found formulas for the threshold fields of studied transitions and their values obtained by the capacitance measurements, the anchoring energy W of liquid crystal molecules on the magnetic particles surfaces, as well as parameter ω, determining the type of anchoring, were calculated. The calculated values indicated the presence of soft, or some intermediate state between soft and rigid anchoring, in studied ferronematic. These results are in agreement with the Burylov and Raikher's theory of thermotropic ferronematics.

The actuality of liquid crystal (LC) materials with supermolecular helix structure studies is caused by their wide using for information display and processing devices, such as large information boards, portable reflective displays etc. The main studies directions are synthesis of new compounds, surface stabilization development, design of new concepts of electronic driving circuits. For a wider use of these materials use it is necessary to solve the problem of complex influence of dielectric anisotropy, supermolecular helix pitch, elastic constants and viscosity on electro-optic effects and phase transitions in these materials. The multicomponent mixtures studies are the most interest and perspective.

Was synthesized two copper (II) complexes and one nickel complex of N-benzylidene-aniline derivatives and their ligands. We have performed polarized FTIR spectroscopy and X-ray diffraction measurements in wide temperature range (0-220°C) in order to establish correlation's among molecular, crystal and mesophase structures. We provided comparison of the FTIR and X-ray diffractometry results between well known metallo-organic copper (II) complexes, which crystallizes in the monoclinic space group C2/c, with similar nickel complex. Investigated ligands and their metallo-mesogens are displaying the same sequence of the liquid crystalline phases -- only with higher melting temperature for metallo-complexes.

A small angle neutron scattering study on the mixture of non-deuterated and deuterated PAA (50%/50%) was performed in the temperature region containing the nematic phase. The measurements were performed with the time-of-flight small neutron scattering spectrometer. The existence of the anomalous increase of the scattered neutron intensity below the clearing point was confirmed. The possibility of attributing that anomaly to the phase transition between uniaxial and biaxial ordering is discussed.

The contrast of antiferroelectric liquid crystal (AFLC) displays working on transmissive mode is degraded by the presence of pretransitional effect. Contrast is significantly enhanced by the use of orthoconic materials, i.e., AFLC mixtures with 45° smectic cone half angle. However, current orthoconic materials usually show short helical pitch (<1 μm), what hinders the surface stabilization of the material with standard alignments. Indeed, cell thickness should be small compared to helical pitch, in order to surface-stabilize the material. Cell thickness nonetheless cannot be arbitrarily chosen, since AFLCs behave as linear retardation plates whose performance is a function of optical path. In the case of transmissive cells, thickness is fixed about 1.5 - 2 μm, i.e., wider than helical pitch. As an alternative, the use of reflective cells has been proposed. In these cells, the optical path is doubled; therefore, the same optical performance can be obtained, in principle, with 0.8 - 1 μm reflective cells than with transmissive cells twice as thick, whereas surface-stabilization is improved. In this work, the electro-optical behavior of orthoconic reflective cells is studied. Multiplexed seven-level driving schemes have been employed for dynamic analysis of orthoconic displays, allowing video-rate multiplexed analogue grayscale.

In this work, the use of antiferroelectric liquid crystals for high-end passive displays has been explored. Antiferroelectric gray levels arise from a double symmetric hysteresis loop that can be stabilized by a constant holding voltage. This driving scheme is passive multiplexing compatible, but limitations appear when the multiplexing rate increases. We have developed new waveforms and driving schemes for high multiplexing level at video rate. The problem of accumulated voltage on bias level arising from data voltages is tackled as well.

A lot of significant discoveries and inventions in the field of technology of displays were made in the latter part of the twentieth century. Apart from well-known CRT, the plasma-, luminescence- and liquid crystal-displays are commercially available. One can notice that a leading position on that flat panel displays market belong to LCD. But the progress in Organic LED materials and devices is impressive. Threshold voltage for light emission have fallen from several thousands V to just 2 - 3 V for today's OLEDs (polymer and small molecule). Luminous efficiency has increased from 0,01 to more than 10 lm/W. These improvements have brought PLED technology to the point where serious consideration is being given to OLED graphic and video display product. The question given some years ago by Dr. M. E. Becker, [Display Metrology and Systems]: "...is the current OLED enthusiasm justified because OLED displays feature significant improvements in visual and ergonomic performance, and because they are much cheaper to manufacture; Or it is just another hope for those who missed the LCD train?...," is trite. During SID Conference in Baltimore in 2003 two companies claiming to have built the largest organic LED. International Display Technology demonstrated a 20 inch display driven by "super amorphous silicon" technology; Sony showed off its 24 inch screen, which consists of a 2x2 tiled array of OLED displays. The presented work will be oriented towards specifying the characteristic features of liquid crystal and electro luminescence organic compounds which make these groups of displays so attractive and prospective among other imagery systems devices existing nowadays.

The prospects of application of polymer-dispersed liquid crystals in information displays are discussed. The brief information regarding methods of preparation of such composites is given. The main electro-optical effects observed in different LC dispersed phases and the effect of PDLC morphology on their electro-optical properties are presented. The advantages and disadvantages of PDLC as materials for construction of different kinds of displays are discussed and the promising applications are shown.

A novel mechanism of photorefractivity in nematic LC cells is presented. Dynamic photorefractivity is based on temporal quasiperiodic modules excitation in the liquid crystal layer by applied external alternating electric field, and their reorientation due to charges induced by interference optical field on a surface of photoconducting orienting layer.

A novel liquid crystal display (LCD) driving concept for light shutters is shown here, based on driving signal polarity reversal controlled by the driving voltage integral across the LCD switching element electrodes, as opposed to plain periodic polarity reversal. This driving scheme optimizes the DC driving signal voltage balancing and guarantees compensation of the long-term (DC) component of the driving voltage within one polarity reversal cycle, irrespectively of driving voltage amplitude variations. The possibility of using low driving frequencies reduces the LCD switching elements power consumption significantly compared to standard driving techniques, which is important for portable devices such as welding light shutters.

Dynamic optical data storage and other applications in the field of optical data processing would be enabled by the development of suitable nonlinear optical materials. In this paper we present an experimental investigation of the orientation photorefractive effect in nematic liquid crystal mixtures with different optical anisotropy and various cell construction layers.

Metal-organic ionic smectices (MOIS) have investigated to find their photorefractive properties. For the first time the multiplexing holographic recording of permanent gratings is obtained in pure lyotropic MOIS. It is proposed new mechanism of holographic recording in ionic smectics involving photo-chemical processes associated with multi-photon absorption. Dynamic grating recording has obtained in MOIS doped by electrochromic impurity (viologen) and in ionic smectic glasses composed by decanoate Co²⁺. A regeneration of viologen from radical state to initial molecule state becomes the main recording mechanism in MOIS with viologen impurity. Electronic absorption of Co²⁺ determines the recording of dynamic gratings in the ionic smectic glasses.

As the phenomenon "color" is involved in almost each production where is a great demand for inexpensive and precise colorimeters. Today there are in principle two kinds of colorimeters: three-channel colorimeters (which are cheap but not accurate) and array spectrometers (which offer a high accuracy at a high price). Liquid crystals have the potential to allow accurate color measurements at a low price. We show three different schemes of colorimeters and actual measurements. The accuracy of our colorimeters is better than 0.005 for each color coordinate.

The sticking effect on photoaligning surfaces was investigated. We demonstrated that additional irradiation of photoaligning polymers with cinnamoil side groups with not-polarized UV-light strongly decreases their sticking parameter. We associate this effect with cross-linking of the flexible side-groups by UV light and, as a consequence, with light-induced strengthening of the photoaligning surface. Restriction of mobility of the flexible groups on the photoaligning surface (surface strengthening) resulted in depressing the sticking effect. The method of the decrease of the sticking effect by the light-induced strengthening is rather general, and it can be applied for any photoaligning materials undergoing a light-induced cross-linking of polymer fragments. For fluoro polyvinyl-cinnamate the light-induced strengthening allowed us to get the record value of the sticking parameter, S₀ = 0.2%, which is better than traditional rubbed polyimide surfaces provide. Such a value of the sticking parameter along with other aligning characteristics allows considering fluoro polyvinyl-cinnamate as very prospective material for modern liquid crystal display technologies.

Multiple pass liquid crystal devices have potential applications as wavelength selective elements for both illumination and measurement systems, the peak in the wavelength transmission of a single birefringence device when repeatedly applied gives a narrow peak in transmission. Most liquid crystal display devices are optimized for operation at 550 nm where the effects of dispersion are of secondary importance, however in applications using multiple devices to create a tuneable filter the effects of dispersion are particularly significant. Typically birefringence data is only available at a specific wavelength or at a specific temperature, this is especially true of commercial liquid crystal that are characterized for 550 nm device operation. To allow computation of both temperature and wavelength dependence the variation of liquid crystal refractive indices over a two dimensional temperature -- wavelength plane has been extrapolated from single wavelength or single temperature data. The effect of this variation in the birefringence of the liquid crystal material in possible filter configurations to determine the wavelength dependence has been evaluated. Though reducing the effective operating range of a given device design a useful tuneable filter function is still achieved. To achieve the same tuning range as would be predicted without the effects of dispersion a more complex stack of devices is required.

According to classical method polyimides were obtained in two-step polycondensation process via 10% solutions of poly(amic acid)s in dimethylformamide (DMF). The indium tin oxide (ITO)-glass plates or glass plates were spin-coated with the 1% (w/w) poly(amic acid)s solutions and then the solvent was evaporated. The aligning polyimide layers were prepared by thermal imidization. Polyimide layers on indium tin oxide (ITO)-glass plates were prepared by thermal imidization at 250°C for 4 h. Their surface free energy and its components were determined. Polyimide films on soda glass with various degree of imidization were prepared by thermal treatment at 180°C, 200°C, 220°C and 250°C. Evaluation of rubbed polyimide layers wettability by four nematic liquid crystals (5CB, 6CB, 6CHBT and 8CHBT) was carried out.

Poly(amic acids) were prepared from chosen aromatic dianhydrides and diamines in dimethylformamide. The glass or the indium tin oxide (ITO)-glass plates were spin-coated with the poly(amic acids) solutions and dried. A thermal imidization process was then carried out. The polar anchoring energy coefficient of 6CHBT molecules on polyimide and poly(amide imides) surfaces was determined by wedge cell method for. The surface free energies and its components were found from van Oss, Fowkes and Owens equations. It was shown that wettability of polymer layers with the 6CHBT and PCB liquid crystals depend on the imidization temperature. The worst wettability was observed for polyimide layers prepared at 250°C, whereas the best for baked at 350°C.

Orienting properties of thin inorganic oxide films created by the method of reactive cathode sputtering in glow discharge plasma are demonstrated. The quality of homogeneous and twist alignment of nematic LC was evaluated by polarization microscopy methods. For comparison of orienting properties of silicon oxide films, the parameter of twist orientation quality was used, and its dependence on technological parameters of sputtering (such as cathode voltage, discharge current density, deposition angle, content of gas atmosphere) was shown. The morphologies of SiO_x orienting layers deposited on substrates with different coatings are demonstrated.

Taking into account that ionic-doped liquid crystals are conductive and the conductance depends on dopant concentration, we suggested using ionic-doped liquid crystals as a electrolytic medium in a described configuration of cell. The application of an ionic doped liquid crystal as electrolytic medium in electrochromic device were investigated. Polyaniline is a conductive polymer and has electrochromic effect in an electrolytic medium under the applied voltage. The spectral investigation of the electrochromic effect of polyaniline was carried out in a new cell. The spectral dependences of such structure were presented on paper. An appearance of electrochromic effect was observed in a structure SnO₂ -- liquid crystal -- polyaniline -- SnO₂.

In this paper the effect of steric hindrance, crosslinking and the use of multipode mesogenic moieties is presented as a part of studies directed on the architectural modification of silicon containing SLCP's. Trist(trimethylsilyl)methyl(trisyl) groups have been attached to liquid crystalline comb-like polysiloxanes by hydrosilylation reaction in order to increase their thermal stability. It was found that attaching trisyl group to 10% of monomeric units led to a decrease in mass loss at 330°C by a factor of 2. The thermo-optical studies of linear and crosslinked LC polycarbosilanes exhibiting SmC* phase proved that crosslinking stabilizes the generated mesophases, especially during isotropisation process. The new synthetic route for polysiloxanes with pendant "triple-fork" mesogenes has been developed. It was found that such the structures are able to generate stable mesophases even if their molecular mass is relatively low.

Laser-induced change in refractive index and optical limiting effect peculiarities have been studied in the liquid crystal systems based on fullerene-doped 2-cyclooctylamino-5-nitropyridine, polyimide, N-(4-nitrophenyl)-(L)-prolinol compounds. Experiments have been made under nano-, pico- and femtosecond pulsed laser irradiation at the wavelength of 532 nm and 805 nm. From the results obtained, both the optical limiting level and nonlinear refractive index n₂ as well as the third-order susceptibility χ⁽³⁾ have been determined. Potentials of the systems studied to attenuate laser irradiation and to record thin amplitude-phase hologram over the visible and near-infrared spectral ranges have been evaluated.

Liquid Crystal Filled Polymer Structure (LiCFiPS) Devices consist of a polymer structure, which performs the desired spatial phase modulation of the incident light, filled with lqiuid crystal to permit modulation of this optical function. Potentially fabrication of this type of device, by established polymer hot rolling or embossing techniques, may be carried out at very low cost. Devices incorporating a complex polymer structure will inevitably have liquid crystal aligned at varying orientations to the surface. Switchable gratings with the liquid crystal aligned in the plane of the grating but either parallel or perpendicular to the grating rulings have been investigated as the two extremes of alignment. Good results have been achieved for parallel aligned devices, however devices with the liquid crystal aligned perpendicular to the grating lines show defects and inhomogeneities. Computational models of these devices show features that correspond well with the observed switching characteristics and have been used to explore routes to the design of improved devices. While such devices might not offer the ultimate versatility of matrix addressed SLM devices they do offer switchable optical devices at very low cost.

The effect of preparation method and properties of components on the polymer-dispersed liquid crystal (PDLC) composite morphology is described. Three different methods of PDLC preparation -- encapsulation, solvent-induced phase separation and photopolymerization-induced phase separation have been studied. Especially designed nematic and chiral nematic mixtures have been used as liquid crystal (LC) materials fulfilling requirements for mutual solubility and refractive index matching of composite components. In all cases the effect of LC concentration and the rate of solidification of polymer binder has been analyzed. It has been confirmed that the mean size of LC droplets is approximately proportional to the LC concentration and inversely proportional to solidification rate. The shape of droplets is usually close to spherical but using special methods one can obtain ellipsoidal droplets. The effect of morphology on electro- and thermooptical properties of obtained PDLC systems has been studied. The correlation between PDLC morphology and possible applications is discussed.

Aqueous solutions of hyaluronic acid (hyaluronan, HA) were studied. The HA compound is a natural polysaccharide, bipolymer. It plays an important role in numerous biological processes as a component of the extracellular matrix, connective tissues and, especially, human and animal synovial joints. Natural and artificial solutions of the HA have demonstrated the viscoelastic nature. These properties are shown to be related to the microstructure parameters (bulk concentration, molecular weight) and external parameters (temperature, stress, shear rate). We emphasize the role of the flow properties of polymeric systems. It is found a liquid crystalline "order" can be "induced" during the material flow. The dynamic properties, such as the elastic shear modulus and viscous shear modulus, are given. These results are discussed in relation to the postulated function of hyaluronic acid in synovial joint and with respect to possibilities o their application in medicine and pharmacology.

New fullerene-doped nematic liquid crystal spatial light modulator with Mg-phthalocyanine nanocrystals has been investigated. Temporal characteristics of this device have been studied. Based on complex formation between fullerene and phthalocyanine, it has been shown that new structure exhibits high speed and operates at supply voltage pulse frequency of more than 100 Hz. A mechanism of a liquid crystal mesophase orientation has been discussed. Potentials of the system for display application have been examined.

The water structure existing in (2-hydroxypropyl)cellulose-poly(acrylic acid)-water (HPC-PAA-H₂O) hydrogel, exhibiting liquid crystalline (LC) organization of the polymer network (anisotropic hydrogel), was assessed by means of Raman spectroscopy. It was shown that the LC-network of HPC-PAA-H₂0 exerts significant influence on the structure of liquid water present in the hydration shells around polymer chains of the anisotropic hydrogel. Due to poor stability of LC-ordering of polymer network, observed in HPC-PAA-H₂O) after its long-term water immersion, the process of crosslinking of the anisotropic hydrogel was considered. The results of Raman measurements revealed that, during immersion of HPC-PAA-H₂O in calcium ions (Ca²⁺) solution, formation of a salt by poly(acrylic acid) of HPC-PAA-H₂O and Ca²⁺ takes place. This results in crosslinking of the anisotropic hydrogel, leading -- in a consequence -- to significant improvement of its mechanical toughness, as well as to stability of LC-ordering of the investigated network in the swollen state. However, during crosslinking of the anisotropic hydrogel (by Ca²⁺), apart from formation of the salt by Ca²⁺ and PAA, the ions influence additionally the structure of the water existing in hydration shells round polymer chains of both polymer constituents (HPC and PAA) creating the anisotropic hydrogel network.

In this paper we present the estimation of average droplet radius in the polymer dispersed liquid crystal (PDLC) film by using optical transparency measurements in electric fields and following calibration by means of the Rayleigh-Gans approximation.