During the last two decades, the number of publications dealing with the synthesis of metallomesogens and the study of their physical properties has increased enormously. The interest is based on new features of these materials that combine the optical and electrical properties of conventional liquid crystals with the magnetic and electronic properties of transition metal complexes. In this paper, we present some aspects concerning the magnetic properties of metal-containing liquid crystals.

The strategies and methods of syntheses of liquid crystalline cyclohexylbenzenes, cyclohexylbiphenyls and bicyclohexylbenzenes are reviewed. The convenient methods for preparations of terminally as well as laterally substituted compounds are recommended.

The novel type of side chain liquid crystal polymers (SCLCPs)--poly(vinylsilanes) with 4-methoxyphenyl-4'- alkenyloxybenzoates were made via polymerization of dimethylphenylvinylsilane and trimethylvinylsilane, followed by functionalization of linear polymers and hydrosilylation of the respective mesogenic alkenes. They form smectic A phase in a broad range of temperatures and their thermal behavior resembles that of SCLCP based on linear polycarbosilane backbone.

A series of new dimeric systems in which various rigid cores are coupled by polar oligoxyethylene and non polar oligomethylene units were synthesized to demonstrate that the internal incompatibility inducing the formation of mesophase may be strongly affected by polarity and volume fraction of the spacer and the mesogenic groups.

The basic structure of 4-[(4'-decyloxybiphenyl-4-yl)-oxycarbonyl]-phthalimide acetic acid methyl ester forming the modulated smectic C phase was modified by introducing changes into the biphenyl group or the substituent attached to the nitrogen atom. The decyloxy chain has been also changed to the carbonyldecyloxy chain. The liquid crystalline phase behaviour of the new ester imide derivatives was examined by DSC, polarized optical nilcoscopy and X-ray diffraction methods. It was found, that addition of a polar group suppressed the smectogemc properties. The compounds having —COO- or —CHN- group inserted between the phenyl rings, formed the nematic phase only.

Liquid crystalline isothiocyanatocompounds have been investigated as components of mixtures for TN as well as STN displays. It was shown that mixtures with low viscosities and short response time can be formulated for both kind of display modes.

A new synthetic approach for the preparation of two- and three ring liquid crystalline compounds possessing trans,trans-dicyclohexyl moiety is proposed and realized. Recently discovered reaction of Grignard reagents with esters leading to 1-substituted cyclopropanoles in the presence of tetraisopropoxytitanium was used as a key stage. Starting from ethyl trans-4-alkylcyclohexancarboxylates the corresponding 6-(4-alkylcyclohexyl)-3-alkyl (or aryl) cyclohex-2-en-1-ones have been prepared. Their catalytic hydrogenation in the base media gave mainly saturated trans, trans-ketones which are liquid crystalline and have been used also as a promising intermediate products for the preparation of different kinds of other LC compounds.

The influence of the polar compound added to the binary mixture with the phase transitions N_re-induced A_d-N was tested by thermomicroscopy. The enhancement or the destabilization of the induced smectic A_d phase was observed after adding 10TPCHB, 6TPCHB, 10CPCHB, 6CPCHB, 10.CN and 10.NCS. It correlates with the behavior of these compounds in binary mixtures with 7BCB.

For many years scientists have tried to study `improper' spontaneous polarization occurred in ferroelectric liquid crystals. In this work we present our theoretical and experimental results concerning behavior of the spontaneous polarization P<sub>S</sub> of several compounds with the `ordinary' spontaneous polarization as well as P_S with sing inversion.

Spontaneous polarization and threshold voltages have been measured for four multicomponent mixtures based on new MHPOBC analogues. Electrooptic measurements were performed using ITO cells having thickness 7 and 10 micrometers . Spontaneous polarization has been measured by reversal current method. It was found that the spectrum of polarization currents depends strongly on the frequency of voltage applied as well as on temperature. Temperature dependencies of spontaneous polarization and threshold voltage have been analyzed using the mean-field theory of the second order transition.

Investigations of a mixture possessing induced antiferroelectric phase are described. This mixture exhibited large thermal hysteresis of the transition between ferroelectric and antiferroelectric phases, which was demonstrated using dielectric and optical methods. Very slow kinetics (ranging from minutes to days) of the transition smectic C^* $ARLR smectic C_A^* was revealed. The coexistence of ferroelectric and antiferroelectric states was noticed. In the investigated mixture the V-shaped switching was observed. The observed phenomena: hysteresis, slow kinetics and threshold-less switching are probably caused by competition of ferroelectric and antiferroelectric interactions acting between smectic layers.

In some mixtures composed of ferroelectric components the induced antiferroelectric phase was observed. Two mixtures of this kind, both exhibiting antiferroelectric order in a broad concentration range, were investigated. The effect of electric field of various strengths on optical properties of these mixtures was studied. In small electric fields the modulation of light intensity occurred, which amplitude in ferroelectric phase was much higher than in the antiferroelectric one. In mixtures with induced antiferroelectric phase we detected a large hysteresis of the transition temperature between ferroelectric and antiferroelectric sates. In high electric fields thresholdless switching was observed in the hysteresis range. The presence of the thermal hysteresis of the C_A^* - C^* phase transition can be considered as a mark of the V-shaped switching. In bulk samples the C^*- phase is stable in, this temperature region, where the V- shaped switching was observed in thin samples.

The measurements described in this paper were carried out in smectic A and C phases of the chiral mixture named W98a. The results of measurements of the tilt angle and the electric permittivity were used to determine the components of the dielectric tensor as function of temperature. The values of the electric anisotropy (Delta) (epsilon) enable us to discuss dielectric torque (Gamma) ^D and its changes caused by temperature and frequency.

Thermal properties of four liquid crystalline substances exhibiting antiferroelectric SmC_A* and ferroelectric SmC* phases were studied using differential scanning calorimetry, texture observation, electrooptic measurements and dielectric spectroscopy. The measurements were performed both on heating and cooling of the samples. All four substances studied in this work are characterized by a complex polymorphism. The temperatures of phase transitions and enthalpy changes associated with them were determined. The transition from the liquid crystalline to the crystalline state showed significant hysteresis for all four substances studied. Textures observations and electrooptic measurements were performed using ITO cells having thickness from 6 to 10 micrometers . The measurements of spontaneous polarization were performed by means of reversal current method. Spontaneous polarization was measured for a few frequencies of the triangular voltage applied. Temperature dependencies of spontaneous polarization have been studied as a function of the side chain structure.

The electrooptical properties of antiferroelectric liquid crystal displays have been investigated. Furthermore it has been observed, that the shape and size of the double hysteresis depend on both the amplitude and the frequency of the applied triangular waveform. Different addressing schemes have been tested to produce analogue grey scales in the display. The influence of the holding voltage, the amplitude of the bipolar waveform and the width of the reset pulse on the switching was investigated. All applied waveforms showed grey scale in the test cells. However, if the holding voltage is too low, the transmission decays with time. Moreover, for optimal holding voltages the transmission remained constant during the frame time. Formation and growth of different domain textures on applied waveforms have been studied.

The aim of our work was the investigating of compounds not having SmC_A* phase, but in their mixtures for some concentration ranges induced smectic SmC_A* was observed. Physical macroscopic properties such as temperature dependencies of the spontaneous polarization P_S, the tilt angle (theta) and the electric permittivity (epsilon) _{(perpendicular}) were measured for three compounds and their mixture. The investigated mixture exhibited antiferroelectric order in a broad concentration range. The large thermal hysteresis of the transition between ferroelectric and antiferroelectric phases for this mixture was demonstrated using dielectric method. We have tried to explain the origin of the induced SmC_A* phase on the basis of the molecular structure of molecules of investigated compounds obtained from theoretical study by using semi-empirical quantum mechanical calculations method MINDO/3.

A compound consisting of banana-shaped molecules was synthesized and well purified. The sample shows the B₂ phase which was characterized by dielectric spectroscopy. Two relaxation ranges were detected. The high frequency one, related to the reorientation about the long molecular axis, was observed in the isotropic phase, too. The increments point to a strong positive dipole correlation in the B₂ state. There are arguments that low frequency mechanism can not be connected with the reorientation about the short molecular axis. AFM-investigations give no hints to a super- structure. Therefore, this absorption was related to a collective response of ferroelectric clusters.

We have made concurrent measurements of ionic current and optical transmission between crossed polarizers on several nematics with positive dielectric anisotropy under the action of applied low frequency (< 1 KHz) square wave voltages. When the field E is low, the measured current is linear in E and there is no electrooptic response. Beyond some value of the field (E₀ approximately 100 esu), the current becomes independent of the field (phenomenon of limiting current). Further an electrooptic signal is measured at twice the frequency of the applied voltage, which exhibits a peak as a function of the field. The width of the peak is 3 to 4 times the value of E₀, and the signal level at the peak decreases as the frequency is increased. These measurements have been made on three highly polar compounds with cyano end groups. Careful observations do not show any evidence of electrohydrodynamic instabilities in the sample. It is argued that the observations can be understood if at the onset of the phenomenon of the limiting current, a strong electric field gradient is established near one of the electrodes due to the sweeping of an ionic species with high mobility. The field gradient produces a flexoelectric deformation of the director field, which in turn gives rise to the electrooptic effect. At higher fields, the stabilizing dielectric torque takes over to suppress this instability.

The following spectroscopic methods used to study of liquid crystals have been discussed: infrared, visible and ultraviolet absorption spectroscopy, fluorescence depolarization. Raman scattering, nuclear magnetic resonance and electron paramagnetic resonance. It has been shown, that using these methods the long-range orientational order in uniaxial liquid crystalline phases as well as some direction-dependent spectroscopic molecular properties of the compounds under investigation can be determined.

According to the papers, liquid crystalline mixtures of achiral mesogen matrix and chiral mesogen additive area of great interest for the investigations of structural and physical properties of twist-grain-boundary (TGB) phases. Such systems allow studying the changes of the structure and properties of TGB phases resulting from the difference in the chiral additive concentration. We used liquid crystalline systems, polymorphism, structure and some physical properties of which had been investigated earlier. Of particular interest was to investigate selective reflection spectra and optical activity of helical smectic A (SmA*) in comparison with the same properties of the neighboring mesophases--a chiral nematic liquid crystal (N*) and a smectic C (SmC*)--with the different temperatures and chiral agent's concentrations. A comparative analysis of obtained spectral and optical characteristics of described mesophases and some conclusions on the peculiarities of the packing structure of these phases have been made in this paper.

The aim of this contribution is to discuss the problem of low frequency electrical conductivity of mesomorphic materials. The subject may be studied in Time Domain technique by means of the excitation of the sample by step voltage pulse. The application of alternating voltage wave is nowadays realized by means of the use of Frequency Range Analyzers. Thus, one can compare the results obtained by means of the methods indicated above. It is assumed that in `small signal case' the results should be equivalent. There exists considerable experimental evidence, that these methods are producing results, which are not in agreement, even, at lowest signals used in experiment. A possible explanation of this discrepancy is proposed.

Preliminary results of the dielectric studies of seven members of the nBT (4-alkyl-4'-isothiocyanatobiphenyl, n equals 4 divided by 10) homologous series are presented. The dependence of the static permittivity (epsilon) _S, the longitudinal relaxation time (tau) _(parallel) and (Delta) H_(parallel)) indicate a hardening of this solid-like smectic phase with shortening of the alkyl chain.

Change in the phase of thermotropic liquid crystals occurs at definite phase transition temperatures. A spectroscopic technique using the Fabry-Perot etalon coupled with a spectrometer has been used to determine the mesophase transition temperatures of the liquid crystal-Cholesteryl myristate. New mesophase transitions have been detected and classified at the temperatures of 52 degree(s)C, 74.5 degree(s)C and 87 degree(s)C in addition to those reported by earlier workers at 71 degree(s)C, 81 degree(s)C and 90 degree(s)C. These findings have been corroborated by the analysis of the thermal runs of the same samples using differential scanning calorimetry.

The molecule of liquid crystal can change its polarizability tensor components in two manners. First, the part of molecule rotates around the other one, and second the electron proton distance in molecule atoms decreases when the temperature of liquid crystal sample increases. The polarizability tensor components (alpha) _(parallel) or (alpha) _{(perpendicular}) include the both changes in their values. In this article we want to separate the both changes. It is possible because the first change is a linear function of temperature. In order to do it we must calculate the quantity (alpha) _{(perpendicular})/(alpha) _PLL which is a linear function of temperature. Knowing the inclination coefficients of these linear functions we have a possibility to calculate (alpha) _(parallel)-(alpha) _(parallel)`) or ((alpha) <sub>PRP</sub> - (alpha) <sub>(perpendicular</sub>)`) in order to obtain the change of polarizability tensor components connected with rotational part of molecule conformation.

Refractive indices n_e, n_o were measured and Lorentz tensor L_(parallel), _{(perpendicular}), anisotropy parameter (tau) equals 1/3 - L_{(perpendicular}), local field tensor f_(parallel),_{(perpendicular}) and order parameter S were calculated for the thirteen tolane derivatives with multiple different configurations in both substituents.

In a matrix of an oligomeric liquid crystal hydrophilic aerosil particles form agglomerates of about 1 (mu) length which consist of aggregates with a diameter of about 150 nm, observed by AFM. In the same matrix, but with hydrophobic aerosil, smaller aggregates with a length-to-breadth ratio 100 nm/60 nm appear. In thicker areas of both samples after heating to clearing temperature and cooling down the cholesteric fingerprint texture occurs, where the lower pitch is observed for the sample containing the hydrophilic aerosil.

The paper presents the results of the measurements of the dielectric relaxation of nematic 6-CHBT performed for different values of the angle between the directions of the macroscopic orientation of the same (director n) and the probing electric field E. Analysis of the evolution of the relaxation spectrum from (epsilon) _(parallel)^*((omega) ) (E (parallel) n) to (epsilon) _{(perpendicular})^*((omega) ) (E (perpendicular) n) allowed one to explain the inconsistency in the molecular interpretation of the spectra. A model of the molecular dynamics in the oriented nematics is proposed.

The paper presents the results of measurements of the static and dynamic electric permittivities (epsilon) _(parallel)^*(T,(omega) ) and (epsilon) _{(perpendicular})^*(T,(omega) ) of 4-(trans-4'-n-hexylcyclohexyl)isothiocyanato- benzene(C₆H₁₃-CyHx-Bz-NequalsCequalsS, 6-CHBT). On the basis of the temperature dependence of the static permittivities, using the Maier-Meier equations, the angle (beta) between the dipole moment vector and the long axis of 6-CHBT molecule, the square of the molecular apparent dipole moment (mu) ²_app and the nematic order parameter S(T), were determined. The dielectric relaxation spectra were interpreted in the frame of the molecular model proposed recently.

The method for the determination of polar anchoring energy coefficient is presented. This method is based on the measurement of the threshold and saturation voltages for electrical Freedericksz transition in the wedge cell. This is a modification of the method described. The method makes use of the fact that thresholds of the Freedericksz transition may be considered as eigenvalues of the operator of the second derivative, corresponding to the boundary eigenvalue problem with different boundary conditions. The method under consideration has been applied to determine anchoring energy of the 6CHTB liquid crystal on various polyimide surfaces. Results have been compared with those obtained by other methods.

The static deformations of a flat nematic liquid crystal cell (modelled as a planar layer infinitely extended in two directions) may be quite precisely described in the frame of the theory proposed subsequently by F.C. Frank, J.L. Ericksen and--in final form--by F.M. Leslie. The deformations are forced by cell boundaries and by external magnetic and electric fields. The quantitative prediction of phenomena is not possible until the nematics material parameters are known; such as the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility, the electric permittivities and the tilt angle of nematics molecules at the boundaries. A stable method for the determination of them is proposed in the work.

The practical applications of the composite method of determination of nematic liquid crystal material parameters (namely the splay and bend elastic constants, the anisotropy of diamagnetic susceptibility and the boundary tilt angle) is presented in the article. The director field value at the nematics cell boundaries is described as a function of the torque transmitted from the deformed bulk, modeling the coupling between the nematics and the substrate. The method is based on approximate solving the coefficient inverse problem. The applied procedure of determination of material parameters may be divided into three stages.

The frequency dependence of the nonlinear dielectric increment was studied for dilute benzene solutions of nematogenic molecules of different polarity: 4,4'-n- hexylcyanobiphenyl (C₆H₁₃-Ph-Ph-CequalsVN, 6CB, (mu) equals 4.8 D) and 4-(trans-4'-n-hexyl- cyclohexyl)isothiocyanatobenzene (C₆H₁₃-CyHx-Ph- NequalsCequalsS, 6CHBT, (mu) equals 3.5 D), at 25 degree(s)C. The increment was induced by the quasi-static electric field of high strength (10⁷ V/m) and its relaxation was detected by the alternating field of low intensity (10² V/m) in the frequency range 1 MHz - 3 GHz. The results were discussed in the framework of Coffey's theory.

The periodic deformations induced by magnetic field in planar nematic layers, which can be observed as stripes, were studied numerically. Two types of deformations were distinguished corresponding to two directions of the field: (1) perpendicular to the layer, (2) parallel to the layer but perpendicular to the initial director alignment. The rigid surface anchoring conditions were assumed. The calculations were performed for various magnetic field strength and elastic constants ratio. Sinusoidal form of the spatial dependence of the angles determining the director orientation, predicted in earlier theoretical works, was confirmed only for sufficiently small deformations. Quite different structure of the stripes was found at high field strengths. The deformation in each half of the stripe was nearly homogeneous. The deformations in neighboring halves had opposite sense. The homogeneously deformed halves were separated by thin `walls' of highly distorted medium. The width of the stripes increased infinitely when the field approached to some critical value. This effect is equivalent to the transition from the periodic to the homogeneous deformations, since an uniformly deformed half of the stripe spreads over the whole layer.

Results of the thermodynamic study of the molecular interaction in Langmuir films of mixtures of 4-n-octyl-4'- cyanobiphenyl (8CB) and 4-pentyl-4'-cyanoterphenyl (5CT) are presented. Both mixed materials are thermotropic liquid crystals and as a single component material is able to form a monolayer at the air-water interface. We demonstrate the effect of interaction of two similar liquid crystal molecules and how the surface pressure is affected by mixing the components in different mole fractions. The surface pressure-area isotherms indicate that 8CB and 5CT are immiscible in whole mole fraction range.

The first seven members of homologous N-(4-n- hexyloxybenzylidene)-4-n-alkylanilines were synthesized, purified and characterized by calorimetric and dielectric measurements during cooling. There are phase transitions between high temperature phases (nematic, smectic A) and the solid-like smectic modifications B and G characterized by different transition entropies and different steps for the relaxation times which can be related to each other. Furthermore a change of sign of the dielectric anisotropy with increasing number of carbon atoms in the alkyl chain was detected. There is also a strong dependence of the activation energies for the reorientation about the short molecular axis on the temperature range of the nematic phase.

The dielectric properties of some liquid crystalline cyanobiphenyls were investigated using dielectric spectroscopy methods in a wide frequency range from 10^-4Hz to 10⁵Hz. There are several significant parameters that can be obtained using this method, such as dielectric permittivity and electrical conductivity. Additionally, nature of the tested material at a given frequency range and for a given electric field range (to 7(DOT)10⁴V/m) was investigated. This nature seems to be rather resistive. However, a capacitive nature becomes significantly responsible for the material behavior in low frequency range--below 1 Hz.

Results of the investigations on PCB liquid crystal as a representative of the nematic simple phase are described in here. Sound speed and sound attenuation the phase transitions (nematic mesophase-isotropic liquid) are measured. Methods of molecular acoustics are used in this research project. Measurement of the sound speed and sound attenuation were performed at 2.5 MHz frequency with an application of the external magnetic field directed perpendicular to the ultrasonic wave propagation or without an acoustic field. These measurements were realized for the phase transitions like mesophase-nematic isotropic liquid and also liquid-isotropic mesophase nematic. Experimental data were analyzed by an application of Fisher method, which allows to find the critical parameters. For same numeric reason we combined two Fisher curves (interpolating curve of the experimental points in nematic mesophase with an interpolating curve for isotropic liquid in mesophase) to obtain a resulting curve. This connection allowed to determine the parameters of a resulting curve and especially the critical exponents and a temperature of phase transition.

The traditional method of evaluation of activation energy leads to its significant underestimation. The correct value of this energy can be obtained using a new method. It is almost doubled in comparison with the old value. This proper value enables to calculate free energy of secondary nuclei. Knowing this quantity value allows calculating other parameters of secondary nucleus like: density of the free surface energy, size and the number of particles in the nucleus.

Liquid crystals have been shown to align on polarized ultra- violet (PUV) exposed polyimide films with the liquid crystal director oriented perpendicular to the polarization direction. Uniform pretilt is generated by a second oblique PUV exposure. Our results indicate that the liquid crystal has uniform pre-tilt with no preferred alignment direction on unexposed polyimide films. Normal exposure aligns the director but the pre-tilt is degenerate, pointing either to the plus or minus direction. Oblique exposure breaks the degeneracy producing a unique pre-tilt direction. The pre- tilt angle is related to the degree of imidization of the polyimide film. By adjusting the chemistry of polyimide, the pre-tilt angle can be varied continuously. Varying the structure of polyimide results in liquid crystal aligning either parallel or perpendicular to the PUV direction. Uniform alignment and pre-tilt can be produced with a single oblique exposure if the liquid crystal aligns parallel to the polarization direction. The photoalignment of liquid crystal on thin films of the azo dye methyl red spin coated on indium tin oxide glass surface is observed for the first time. Methyl red molecules are believed to first adsorb on the substrate with an isotropic orientation. After exposure with polarized visible light, the elongated structure of the molecule results in dichroic absorption of the light by molecules oriented parallel to the polarization direction. Our study shows that photo induced cis/trans isomerization process produces the preferred alignment of methyl red and therefore the liquid crystal perpendicular to the polarization direction.

A method of preparation of polymeric substrates with a given surface relief is proposed. While elongating a polymer matrix with a hard coating at temperature lower than the glassing point a periodical structure is generating. The influence of structure period, depth and material on LC alignment is considered. Advantages of LC cells proposed are light weight, chemicals and shock stability, wider range of viewing angles.

A new one-side-rubbing in-plane switching (OSRIPS) mode has been developed. We discuss the displaying structure and mechanism, introduce the process of experiment and measurement. The result expresses that the OSRIPS mode has good viewing angle and grey level characteristics, especially it completely suppresses the color shift.

We studied electro-optical characteristics of the liquid crystal (LC) cell with weak planar anchoring of the director with bounding substrates. The weak surface anchoring let us to decrease the cell driving voltage. Moreover, because of the absence of the strong subsurface director deformations, the cell could operate in the Mauguin regime. Using these we proposed a new type of the LC switching mode--the in-plane sliding mode. We realized this mode in the LC cell comprising of one reference substrate with strong director anchoring and one photoaligning material-covered substrate with weak anchoring.

Polyimides from four selected dianhydrides and seven diamines were synthesized by two-step polycondensation method. During the first step 10% solutions of poly(amic acid)s in N,N-dimethylformamide and 1-methyl-2-pyrrolidinone were obtained. The thin polyimide layers on soda glass were prepared by thermal cyclodehydration. Contact angles of series of standard liquids for tested polyimide films were measured. The values of surface free energy and its components were calculated accordingly to Zisman, Owens et al. and van Oss equations. Some correlation between the surface properties and the chemical structure of polyimide aligning layers were presented.

The group of poly(ester imide)s characterized by various chemical structure has been synthesized by reaction of carboxyimides (or their chlorides) and diols (or their derivatives). Some properties of the obtained polymers were examined. Among them the adhesion to glass, through reluctance and thermal resistance were tested. The quality of model nematic liquid crystal alignment of the polyimide layers by using the interference wedge method was tested. The relationship between the chemical structure of examined polyimide aligning layers and their properties was discussed.

In the work consideration is being given to inhomogeneity of LC orientation at the profiled-surface relief gratings. Its effect on the diffraction characteristics of gratings is analyzed. It is demonstrated that for switchable diffraction elements with LC this effect may be neglected in quite a number of cases.

Accurate optical method for measuring twist angle in TN LC cells is developed. Deviation of the measured values at different orientation of the cell and polarizes have been analyzed. The method allows to determine twist angle with high accuracy for cells with rubbed surfaces as well as for cells where at least one surface is grooved.

A new method for making displays with well defined thickness of the liquid crystal layer is described. This method is capable of making rigid displays with variable gap and is distinguished by simplicity and reliability. Display color variation with the observation angle is studied for different electrooptic effects.

The paper describes the application of a Surface-Stabilized Ferroelectric Liquid Crystal (SSFLC) cell as a polarization switch in a frequency stabilization system of a Zeeman laser interferometer. The FLC cell is used as a field-controlled (lambda) /4 plate in which the optic axis can rapidly alternate between two positions, thereby alternatively switching either of two orthogonal radiations into the same measuring channel. The high switching speed of the FLC is here a key feature as it allows several thousand such calibration measurements to be performed in a second.

The paper presents further development of a high-voltage multichannel waveform generator especially designed for driving all kinds of liquid crystal devices. In its basic mode of operation the instrument offers full freedom of on- line editing of the addressing waveform down at the pulse level. The connected liquid crystal cell is protected from undesired transient signals by utilization of two memory banks. With its eight channels, the generator can physically drive a 4 X 4 matrix as if it was a part of a much larger display.

The absorption spectra of some dichroic dyes: derivatives of naphthalenebicarboxylic acid and of naphthoylenobenzimidazole in nematogenic liquid crystalline mixture ZLI 1695 have been studied in details using polarized light. On the basis of these spectra the order parameters S and D have been determined by using the theoretical relation D equals f(S) and proper calculation procedure. Moreover, the absorption transition moment directions with respect to the long axis of the dye have been assigned.

The present work contain the studies on optical parameters (contrast ratio, viewing angle, birefringence and brightness) of twisted nematic display with black dichroic dye which is designed for an application in large-area information and advertising systems. The numerical optimization of display with a dye has been done. The absorption characteristic of the dye has been obtained. Birefringence of doped mixtures (Delta) n has been measured. The contrast ratio of doped mixtures has been measured in wide temperature range from -25 degree(s)C to +70 degree(s)C. The angle characteristics of contrast ratio for +20 degree(s)C have been obtained. In the work the detailed results describing the effect of a dye on temperature dependence of birefringence and contrast ratio, moreover, the effect of dye on the viewing angle for the first and second transmission minimum will be presented. Additionally, the dielectric characteristics of different mixtures will be shown.

Mechanism of holographic dynamic grating recording in a thin cell with dye doped nematic liquid crystal under laser light has been proposed. Nematic liquid crystal with dye is sandwiched between two coating glass plates covered by ITO conductive and polyimide orientation layers. In this experiment, two interfering laser beams induced spatial modulation of refraction index and form interference pattern in the liquid crystal cell. The recording mechanism is linked with DC electric field driven reorientation of nematic director and induces the bulk photoconductivity of the system.

We have described the relation between LC parameters and induced diffraction gratings recorded by light intensity pattern in dye-doped nematic liquid crystals sandwiched between two coating glass plates covered with ITO conductive and polyimide orientation layers. In our investigations we used the LC cells containing planary oriented nematic mixtures (low-angle rubbing, tilt 1.5 - 2%) doped with the antraquinone dyes (0.1 - 1% w/w). Nematic liquid crystal mixtures with different electrooptical threshold, optical anisotropy, viscosity and conductivity have been investigated. The influence of resistivity, optical anisotropy of LC mixtures and polyimide layers on diffraction efficiency and other parameters have been discussed.

Induced by nanosecond pulses of second harmonic generation from Nd:YAG laser the hydrodynamical instabilities in planar- and twist-oriented layers of the nematic 6CHBT doped with anthraquinone dyes under dc electric field in the region above the Freedericksz threshold were revealed. The dependence of diffraction efficiency on voltage is characterized by the two maxima which are corresponding to the two types of EHD-instabilities that have two characteristic decay times, one of them is of the order of 100 ms and second one is equal to several milliseconds.

Orientation of director field can be obtained by liquid crystalline (lc) waveguide application. The method has been described earlier. As it is new approach verification of the results in an independent experiment is presented here. The retardation measured in tunable lc retarder has been used to do such verification. Calculations of the retardation made with director field profile measured in the lc waveguide has been compared with measurement results obtained in the lc retarder.

Effects of curing temperature and UV intensity on electro- optic properties of polymer stabilized cholesteric texture reverse-mode light shutters have been studied. Scanning electron studies indicate that increasing the curing temperature generally results in a larger average mesh size within polymer networks. The cell polymerized at correspondingly low temperature has a stable OFF state (planar texture) while the driving voltage is high. Increasing the curing intensity results in a more dense network and the strands are smooth and thin. The cells prepared with low UV intensity exhibit high contrast and low driving voltage, while the response time is slower than those prepared with high UV intensity.

We present a design scheme for new type of color reflective Liquid Crystal Displays. In our scheme, the ambient light is collimated by micro-pyramid structure and high reflectivity can be obtained by using Optic Interference Film. It is clear from calculation and analysis that high reflectivity and excellent chromatic characteristics are obtained. In this paper, we will give out the simulative calculation and analysis results of this scheme.

The microstructure of the polymer composite based on the LC- cellulose derivative and poly(acrylonitrile) was investigated. The polymer composite was obtained by photopolymerization of the mechanically oriented (shearing) lyotropic LC-solution of the (2-hydroxypropyl)cellulose (HPC) in the acrylonitrile (AN). The use of multiple techniques: dielectric, thermogravimetric, mass spectroscopies, and thermooptical analysis enabled to overcome resolution problem related to behavior of the non- mesogenic polymer network of poly(acrylonitrile) in the mesogenic environment of the HPC. The results of the investigation of the composite microstructure show that the polymer composite is composed of two subsystems: mesogenic system of cellulose derivative and oriented fibril-like polymer network which is formed by non-mesogenic poly(AN). The polymer network of poly(AN) influences the optical anisotropy relaxation of the mesogenic HPC in the composite.

The temperature dependences of the elastic splay K₁ and bend K₃ constants and birefringence (Delta) n of a comblike combined side- and main-chain polymer near nematic (N)--smectic A (S_A) phase transition were investigated using the method of the Freedericksz threshold transitions. Experiments were performed on a series of fractions in the range of molecular weight from 900 to 10200. The splay constant K₁ and birefringence (Delta) n have practically normal `nematic' temperature dependence in the investigated temperature range. For some fractions near the N$ARLRS_A transition, the bend constant K₃ exhibits a rapid increase with decreasing temperature, which is explained by the fluctuations of smectic order in the nematic phase. For high molecular weight fractions, the fluctuation-dependent part of K₃ varies as (T - T_N-SmA)^-(rho ) according to theoretical predictions. Hence, the values of critical exponent (rho) are very large (1.1 - 1.4). For low molecular weight fractions, no agreement is observed between the results obtained and theoretical predictions. The features of critical behavior of bend elastic constants of liquid crystal investigated may be explained by the molecular weight polydispersity of polymer fractions.

This paper presents a synthetic pathway leading to a new class of materials--crosslinked acrylic-polydiethylsiloxane copolymers. They combine the mesomorphic properties of long alkyl-substituted siloxanes with well defined acrylic/siloxane networks. In order to obtain telechelic bis(3-aminopropyl)-oligodietythylsiloxanes, the equilibration reaction of nexaethylcylotrisiloxane with bis(3-aminopropyl)-tetramethyldisiloxane has been studied. The next synthetic step of the synthesis involved the addition of amino terminated oligosiloxanes to vinyl isocyannates leading to UV-crosslinkable vinyl macromonomers. Several crosslinking reactions of the vinyl terminated oligosiloxanes in acrylic matrix have been carried out. Variable proportions of siloxane and acrylate components led to the mesomorphic elastomers with different mechanical properties.

The aim of this study is presentation of thermodynamic analysis of polymerization induced phase separation for a previously investigated (8 - 11) PDLC consisting of nematic LC mixture (W-52a and 6CB) dissolved in unsaturated oligoester resin. That is polymerized by UV radiation to form photosetting polymer matrix. The analysis of the separation is focused on polarized optical microscopy determination of cloud-point. The separation temperature is dependent on weight fraction of LC in the blend with oligoester. The value (for the same weight fraction) depends strongly on polymer conversion. Flory-Huggins interaction parameter (chi) (calculated from spinodal equation) is dependent on temperature according to equation: (chi) _(T) equals C_(p) + D_(p)/T; where C_(p) and D_(p) depend on a conversion degree of the polymer. Additionally T_g and T_NI of LC changing in the course of matrix polymerization were found.

A new method is proposed for increasing contrast and modulation depth of liquid-crystal electrooptical materials on the basis of the production of a polymer dispersed liquid crystal monolayer in which the interference effect of quenching for coherently scattered light is realized. A dramatic increase in the contrast ratio at viewing angles up to 5 degree(s) is predicted theoretically. The results of calculations for surface ferroelectric liquid crystal droplets films in the anomalous diffraction approach are presented.

The results of studies on a preparation of new thermosensitive polymer-dispersed liquid crystal films are presented. The studied chiral nematic materials and polymer systems are described. Obtained results are compared with conventional systems containing cholesterol esters and discussed from an application point of view.