Ferroelectric liquid crystals (FLC) are to conventional liquid crystal what Gallium Arsenide is to Silicon in the semiconductor area. The first generation of FLC displays in now present on the market and has some outstanding features based on the symmetric bistability which may be achieved in these materials. One of the greatest challenges for the next generation is to achieve an analog grey scale out of an essentially digital principle. We will analyze in some detail which major problems had to be solved to reach the present state and show how the final steps could be taken toward a new state-of-the-art level in liquid crystal devices. In the last decade university research and industrial R and D have almost equally contributed to treat the very serious complications caused by the so-called chevron structures We will review this important topic in particular detail.

Dielectric dispersion has been studied in the frequency range of 10Hz divided by 1MHz in liquid crystals with 2- alkoxypropriate chiral group. Two of them exhibit the spontaneous helix twist inversion in the SmC* phase. The dispersion reveals two modes, dielectric strengths as well as relaxation frequencies of which exhibit a strong dependence on the sample thickness. Mode 1 with the relaxation in the kHz range is the Goldstone mode, which is combined with a thickness mode, but it becomes the pure thickness mode in the temperature range near the helix twist inversion temperature, where the helicoidal structure is unwound. This situation is reflected in the temperature dependence of characteristics parameters of mode 1. The lower frequency mode 2 is attributed to a mode connected with a non-homogeneous distribution of ionic space charge, which is localized near the sample surface.

A new method for investigating the dynamics in free-standing films of ferroelectric liquid crystal in the range of 5 Hz to 10⁵ Hz by means of optical reflectivity is presented. The experimental results were obtained by applying electric AC fields up to 43 V/cm to the films. By measuring the magnitude and phase of the dynamic reflectivity, a relaxation process was found at frequencies below 1 kHz originating from the Goldstone mode. In a 73 layer film the process is still detected several degrees above the bulk phase transition temperature S_C* to S_A, which can be understood by a surface ordering effect.

For the relation between the sign and size of the helical twisting power (HTP) and the absolute configuration of a chiral molecule, a couple of different effects are responsible which contribute with different weighting factors to the induction of the pitch of a cholesteric phase. With the concept of decomposition of the chiral induction in an intramolecular and intermolecular chirality transfer two of these effects, the independent contribution of chiral groups within the dopant - far away form each other - to the HTP and the dependence of the HTP on the orientation of the orientation axis with respect to the molecular skeleton of the dopant have been analyzed.

Application of both the conservative rapid scan and a novel step-scan Fourier-transform spectroscopy enables us to follow the intra- and intermolecular motion of ferroelectric liquid crystalline polymers and elastomers during electro- optical switching on a time scale from seconds down to microseconds. It has been detected that although all molecular parts move synchronously in course of the switching, the amplitude of such motions is different. The obtained results are discussed in terms of the role played by the molecular segments during the process of reorientation.

The discrete phenomenological model of antiferroelectric liquid crystals is reviewed that takes into account interlayer interactions up to next nearest neighboring layers. Possible predicted tilted phases are presented and compared with experimentally observed phases: the ferroelectric SmC* phase, the antiferroelectric SmC_A* phase, the ferrielectric SmC_(gamma )* phase and the short pitch SmC_(alpha )* phase. It is also shown that various observed sequences of phases in dependence of temperature can be obtained by properly choosing the model parameters.

In this paper some electrooptic properties such as the spontaneous polarization Ps, and tilt angle and dielectric measurements are described for a novel ternary ferroelectric liquid crystal mixture based alkoxyphenyl esters and alkoxy- benzoic acids. A theory of dielectric response is presented and the suggested model is in good accordance with the values of elastic constant and switching time respectively.

Some multicomponent ferroelectric mixtures have been prepared and characterized. Novel non-chiral and chiral non- mesogenic fluorine containing ester derivatives were mixed with chiral compounds and binary mixtures exhibiting smectic C phase. The physical and electrooptical properties such as tilt angle and switching time were also measured.

The dielectric response of thin surface stabilized ferroelectric liquid crystal cells with different aligning materials and filled with the same FLC mixture are studied and compared in the low frequency dielectric regime. For the measurements we adopted an improved cell structure with metallized pixel connections. In the FLC material in question, Merck SCE 13, only one absorption appears corresponding to a collective mode.It is ascribed to the Goldstone mode in the bulk FLC. From our measurements we calculate the surface anchoring energy density for the different aligning materials and discuss changes induced in dielectric spectra by a DC bias field.

Two kinds of twist grain boundary (TGB) phase have been observed until now: TGB-A and TGB-C, which are composed of grains, possessing the local structure of smectics A and C, respectively. According to Renn's theory, the third TGB phase may exist in the vicinity of the chiral NAC-point: the TGB-C* phase with the local smectic C structure. We investigated several mixtures possessing chiral NAC-point. In few systems of this kind we observed two TGB phases in place of the N*AC* point. One of these phases was the TGB-A phase. The other phase exhibited textures typical for both TGB and smectic C* phases. Texture observations and light diffraction experiments suggest that the low-temperature TGB phase might have the TGB-C* structure predicted by Renn.

In the present work the dielectric relaxation related to non-collective motion of liquid crystal molecules has been studied. In the first pace we observe the relaxation around the short axis for a choice of ferroelectric and antiferroelectric materials.Additionally, for some material the non-collective motion around the long axis has been investigated. We found that for all investigated compounds, except one, the relaxation obey an Arrhenius las f equals f=0) exp(-E_a/kT) and we were able to map the activation energy changes between different smectic phase. The changes of the activation energy E_a are related to the parallel correlation between the molecules. For most of the investigated ferroelectric material we observed that the correlation increase both along the long and short molecular axes at the phase transition to the smectic C* phase. For antiferroelectric materials the parallel correlation along the long axis weakens in the smectic C_a* phase. It thus seems that antitilt layer structure is related to the low degree of molecular correlation.

Dependence of SSFLC electrooptic switching characteristics and matrix addressing capabilities on cell materials was investigated. Four test cells were made with two FLC mixtures, ZLI 4851-000 and BDH SCE8, in combination with two alignment materials, rubbed polyimide and friction deposited teflon. The cells show a good bistability characterized by memory and symmetric switching. Delay and rise times have been measured and fitted using a uniform director model, allowing a determination of all parameters within this model. Based on this, computed regions of operation of normal and fast addressing modes are reported. For both mixtures, teflon aligned cells, compared to polyimide aligned cells, show higher elastic restoring torques in the model. For normal addressing modes, teflon cells feature a higher minimum and a lower maximum operating voltage. Furthermore, they allow higher addressing speeds for both normal and fast modes.

Investigations of the features of thickness dependence of optical activity of dye-doped chiral liquid crystals (DCLC) were accomplished on the wedge and parallel cells filled with either pure or dye-doped nematic chiral mixtures. A method of precise calculation of spectral dependences for both angle of polarization plane rotation and ellipticity for the light passed through the DCLC film was developed. Nonlinear thickness dependence of the angle of polarization plane rotation was established with differing proportionality coefficients for the bigger and smaller LC layer thickness. Changes of polarization state of light while passing through the CLC film were observed for both types of circular light polarization. The influence of the dopant absorbing within selective reflection band on different optical characteristics is discussed.

Two mixtures: W-90 and W-91 containing an epoxy compound as a chiral dopant have been studied using dielectric and electrooptic methods. W-90 mixture shows a phase sequence Is-N^*-SmC^* whereas W-91 mixture - Is-N^*- SmA^*-SmC^*. One of the objectives of the paper was to study the transition order between ferroelectric and paraelectric phases. Dielectric spectra were measured using 10micrometers EHC cells. In SmC^* phases of both mixtures a broad Goldstone mode dielectric spectrum has been found. Switching properties of both mixtures have been studied by using LINKAM 5 micrometers thick cells. Tilt angle and spontaneous polarization have been measured in the SmC^* phase versus temperature. Dielectric and electrooptic data are discussed in terms of the mean field model.

Oscillation processes have been revealed in the course of reversible polarization study in ferroelectric liquid crystals. The oscillation frequency of polarization vector has been found to be from 1 to 30 kHz. The oscillation parameters were studied as functions of temperature. Temperature dependences of the oscillation amplitude and damping decrement have been measured.

Ferroelectric liquid crystals with high enough spontaneous polarization exhibit a special periodic structure which forms after switching off a moderate electric field. One of the most important features of this new structure is the existence of inclined smectic layers with opposite signs of the inclination angle (delta) . In this contribution we present the results of our recent dielectric and pyroelectric investigations in the FLC-mixtures with different value of the spontaneous polarization. The temperature and BIAS dependencies of the relaxation strength and critical frequency of the domain mode process in the different mixtures was worked out. The suppression of the domain mode process was investigated using dielectric and pyroelectric technique.

We have studied the order parameter dynamics close to the SmA-SmC^*_A phase transition in homeotropic cells of 4-(1-ethylheptyloxycarbonyl) phenyl-4'-alkylcarbonyloxy biphenyl-4-carboxylate by photon correlation spectroscopy. The order parameter fluctuations in the antiferroelectric SmC^*_A phase can be decomposed into the fluctuations of the phase and the amplitude of the molecular tilt angle. Considering the unit cell to consist out of two adjacent layers, one can describe these fluctuations with two ferroelectric modes and two antiferroelectric modes. Using photon correlation spectroscopy we measured both ferroelectric phase modes in the backward scattering geometry. This is the first simultaneous observation of these modes. The temperature dependence of the relaxation rates of these modes gives the coupling coefficients of the ferroelectric and antiferroelectric order parameters, whereas the dispersion relation leads to the values of the diffusivity coefficients for antiferroelectric and ferroelectric phase modes in the SmC^*_A phase.

Within the framework of the phenomenological model that takes into account the interactions between the smectic layers explicitly, we analyze the structure, the transition temperatures and the macroscopic polarization of the free standing film formed by an antiferroelectric liquid crystal. Outer layers of the film interact only with the interior of the film and are therefore less tilted. Consequently, the transition temperatures from the tilted phase to the untilted smectic. A phase are lower than for bulk samples. Due to the chiral interactions the film possesses the macroscopic polarization which is for even lower than for bulk samples. Due to the chiral interactions the film possesses the macroscopic polarization which is for even number of layers parallel to the plane of the tilt, while for odd number of layers it is nearly perpendicular to the plane of the tilt.

Dielectric, electrooptic and pyroelectric properties of unknown SmX^* phase of (S)-(1-propyl-oxycarbonyl) ethyl 4(dodecyloxythiobenzyloxy) benzoate are studied. Low frequency dielectric studies performed with a 10micrometers EHC cell show that this SmX^* phase exhibits an induced Goldstone mode dielectric spectrum. The spectrum is a single Debye-Type process with the relaxation time of the order of 10^-5 s. The intensity of the spectrum increases non- linearly with the bias field strength. Studies of pyroelectric coefficient in the vicinity SmA^*-SmX^* transition show, that the SmX^* phase is not a typical ferroelectric or antiferroelectric phase, and that the character of the transition depends on the field strength applied.

Binary mixtures of achiral liquid-crystalline copper complexes with a chiral nonmesomorphic dopant were prepared. The achiral copper complexes incorporating Schiff's base ligands show enantiotropic smectic C and smectic A mesophases. A study of the ferroelectric properties of these materials was performed. The spontaneous polarization P_S and the switching time were determined by means of the polarization reversal method. The dielectric behavior of one copper compound was investigated by dielectric relaxation spectroscopy in the frequency range from 10 Hz to 13 MHz. It exhibits the Goldstone mode, the soft mode, and a molecular mode.

Chiral nematic polar mixtures (7BCB-7CN)-5^*CB were investigated by visual and spectrophotometric methods. It was found that these systems have a reverse temperature dependence of selective light reflection. The wavelength of reflected light increased with the temperature increase. The bicomponent mixture containing 5^*CB and non-polar 805, showing enhanced A₁ phase, had a normal spectral characteristics. The color of reflected light changed from red to blue with temperature increase in the neighborhood of S_A1-N^* phase transition.

The helical pitch for cholesteric and ferroelectric Sm C^* phases has been measured. For cholesteric and also for Sm C^* measurements have been done for several mixtures characterized by various concentration of chiral molecules. They have been done in planar geometry for cholesteric phase and in homeotropic geometry for Sm C^* phase. Measurements involving reflection and transmission modes have been carried out. It has been used Grandjean-Cano method. We have done conoscopic and orthoscopic observations. Sign of the chirality has been found by Airy's spires method.

The rotational viscosity γ_φ has been studied for SmC* phase of ferroelectric liquid crystal mixtures containing a different amount of the same chiral dopant. Goldstone mode rotational viscosity γ_φ has been determined by two different methods. The first one is an electrooptical method, the second is a dielectric method using samples with unperturbed helicoidal structure. This method is based on measurements of Goldstone mode dielectric strength and relaxation frequency supplemented with values of the spontaneous polarization, the tilt angle. The rotational viscosity has been presented as a function of chiral dopant concentration and as a function of temperature. Results have been discussed in context of the dynamics of the structure under electric field.

Electrohydrodynamic convection in freely suspended smectic films is investigated experimentally by means of reflection polarizing microscopy. A 2D vortex flow is observed when an electric field is applied in the plane of the smectic layers and the electrodes are in contact with the film. This type of convection has been studied in smectic A, nematic and isotropic films before. For the first time we present measurements of the vortex mode in smectic C^* films and ferroelectric smectic C^*-films. The connective flow within the optically anisotropic smectic C layers can be visualized directly due to the optical textures resulting from the non-uniform c-director field. In ferroelectric smectic C^*-films additional director reorientation effects due to the interaction between the applied electric field and the spontaneous polarization are observed.

The database LiqCryst 2.1 contains chemical structure and physical properties of about 70000 thermotropic liquid crystals, extracted from 14000 references. Program and data represent a scientific tool which allows statistical analysis of structure-property-relationships and the prediction of phase transition temperatures by an similarity approach.

The image-sticking caused by the asymmetry and shift of current-voltage (I-V) characteristics of the MIM element is a big problem in MIM-LCD. The I-V characteristics couldn't be described accurately and comprehensively by conventional Poole-Frenkel equation, so it is difficult to estimate and optimize various parameters to solve the problems, which means the optimization of the parameters requires many experiments with much effort. In this article, considering the effect of the two interface layers which exist between the two electrodes and the intermediate layer, we introduce a p-n-n⁺ band model. Using this model, we can explain the reason of the asymmetry and why it is easier to produce Poole-Frenkel effect from the top-electrode to the bottom- electrode than it does on the opposite direction. Meanwhile, we propose that using the weaker electronegative metal as top-electrode or using the sputtered tantalum oxide instead of the anodized tantalum oxides as insulator layer can solve the problem.

Thermotropic liquid crystals (LCs) in the nematic phase can often be induced to have a cholesteric phase by addition of molecules having chiral characteristics, such as the binaphthyl class of molecules. The study of such phases is made difficult by the lack of knowledge about the behavior of such molecules. For example, finding relatively simple properties such as exact structures, the important factor being the dihedral angle between the binaphthyl groups, to dipole and quadrupole moments are hampered by the difficulty in performing accurate calculations or experiments. In this paper we present results of first principle electronic structure calculations on the binaphthyl molecule and also on its nitrate. We have calculated accurate structural information, and in particular calculate the total energy of the molecules and the dipole and quadrupole moments as function of the dihedral angle optimizing the structure at each point. We also discuss the changes to the molecular and electronic structure when certain terminal groups are added to the molecule. Accurate energetics and structural information on the molecular/electronic level such as this leads to accurate modeling potentials for large scale empirical computations.

We determine accurate molecular structures, dipole moments and intramolecular potentials for mesogenic fragments and liquid crystal molecules from quantum mechanical computer simulations performed on 256 nodes of a Cray T3D. We employ density functional theory and use ab initio pseudo potentials for the interaction between valence electrons and ions and the generalized gradient approximation to account for the many-body effects of exchange and correlation. Periodic boundary conditions are enforced so that the molecular electronic wavefunction can be expanded in terms of a plane wave basis set. We parameterize a torsional potential for rotation about the dihedral bond for the mesogenic fragment 2-2' difluorobiphenyl with full structural optimization and demonstrate the influence of conformation on the molecular dipole moment. We also calculate the dipole of the nematogen 4-4' pentyl cyanobiphenyl and various fragments.

We have used a direct correlation function approach to evaluate the elastic constants for the Gay-Berne discotic nematic phase from microscopic data, obtained from constant pressure Monte Carlo simulations.

We have performed Monte Carlo simulations for elongated molecules assuming an ideal orientational order. The intermolecular forces were derived form the Gay-Bernes model, where the long molecular axis were taken parallel to the z-direction. Additionally, we included dipole-dipole interactions by adding permanent dipoles along z. The dipoles were allowed to be oriented either up or down, similar to spin configurations in the Ising model. Their interactions were evaluated by using the Ewald summation technique.By changing temperature and the magnitude of the molecular dipoles we found an ideal nematic phase, smectc A¹ or A² phases.

Under the influence of a weak electric field the unit cells of the cubic blue phases are continuously deformed. We propose a complete description of this phenomenon, known as electrostriction, within the frame of the standard Landau- Ginzburg-de Gennes theory for cholesteric liquid crystal.

Continuing previous work, we present here the phase diagram of a binary mixture consisting of a nematogenic solvent and a solute of spherical particles obtained using the Monte Carlo computer simulations. In this mixture the rod-like particles interact via a Lebwhol-Lasher potential while the spherical particles are represented by vacancies; all particles are located on the sties of a simple cubic lattice. There are two types of motion allowed, namely rotation of the rod-like particles and exchange of lattice positions between a pair of solute and solvent particles. Various exchange procedures ensuring preservation of microscopic reversibility conditions between unlike particles have been investigated and the one leading to computationally fastest convergence of various averages identified. Simulation results suggest a broader region of uniform nematic phase which transforms directly into the isotropic phase at a higher temperature in contrast to the molecular field prediction of a narrow single nematic phase surrounded by the nematic-isotropic coexistence region. Moreover there was no evidence of any biphasic region just below the clearing point although demanded by the first order nature of the phase transition. For mixtures with a solute mole fraction higher than 40 percent, only one weak transition, which apparently is that of a biphasic into the isotropic phase, was observed.

The time evolution of cylindrical domain walls in nematic liquid crystals is analyzed by means of a polynomial expansion of the director field. Analytical solutions are obtained for shrinking of the cylinder radius and the change of the wall width.

Application of high pressures to a molecular system modifies the intermolecular potential due to changes in the average intermolecular distances. That causes considerable changes in physical properties of the system. Recently we have performed high pressure dielectric studies of several liquid crystals exhibiting the nematic, smectic A and smectic B polymorphism. In the article we present some result demonstrating the influence of pressure on the dielectric anisotropy, dielectric relaxation time characterizing the molecular reorientations around the short axes and related activation parameters, and on the nematic potential. Some differences in the behaviors of particular substances are interpreted as caused by the details of molecular structures and intermolecular interactions.

The results of dielectric studies of 6BAP(F) in the nematic and isotropic phases are presented. The substance has a negative dielectric anisotropy. The use of two experimental techniques, network analyzer and time domain spectroscopy, allowed to separate of two main relaxation processes: one connected with the molecular reorientations around the short axes and the second with rotations about the long axes, in the nematic as well as in the isotropic phases of 6BAP(F). The relaxation times and activation enthalpies for particular motions were obtained. The retardation factors characterizing the influence of the nematic order on both reorientations were calculated.

With the aid of differential thermal analysis the phase diagram of trans,trans-4'-n-heptyl-bicyclohexyl-4- carbonitrile (7CCH) established up to 200 MPa, shows stable crystal, nematic and isotropic phases. Dielectric studies on the static and complex permittivity have been performed in the frequency range 1 kHz-13 MHz up to pressures of 200 MPa. The activation parameters for the nematic phase. We find a trend of increasing values for the activation parameters, the retardation factor and the nematic potential, when we compare the heptyl series 7CB, 7PCH, and 7CCH.

The paper shows that the behavior of dielectric permittivity and its changes in a strong electric field can be described in the way analogous to that applied in critical binary solutions. Basing on measurement in 4,4-n-hexylcyanobiphenyl and 4,4-n-tetracyanobiphenyl (4CB) it was possible to portray the temperature behavior of dielectric permittivity and NDE from T_c + 50 K. IN the case of 4CB the satisfied description was possible despite the fact that the sample crystallizes before reaching the clearing point. NDE tests was conducted for the measurement frequency f equals 70 kHz, what allowed to avoid the in fluence of relaxation processes on results.

With the use of recently developed dilatometric cell pVT data are established for the crystalline, nematic and isotropic phases of 4-n-pentyl-4'-cyanobiphenyl (5CB) up to 300 MPa. A stable and a metastable crystal form can be distinguished. Previous dielectric measurements on 5CB² are extended to higher temperatures with the aid of new dielectric cells, and to higher frequencies that allows one to analyze in more detail the dielectric properties in the isotropic phase. From the dielectric relaxation in the nematic and isotropic phases we derive the activation quantities in the usual way. The paper demonstrates the usefulness of pVT data which are indispensable to separate the different influences of temperature and density.

Dielectric relaxation spectroscopy has been sued to study the molecular dynamics of three nematogens, derivatives of bicyclo (2,2,2) octane with -NCS terminal group, in the nematic and isotropic phases. It has been found that the dielectric spectra in the isotropic phase and in the nematic phase can be resolved into three components, described by the Debye functions. The possible molecular reorientational movements responsible for the relaxation processes related to these components are discussed.

Dielectric studies of nematic liquid crystals (NLC) have proved to be a valuable source of information on the mesomorphic, liquid crystalline phase. Oriented samples of liquid crystal are dielectrically anisotropic, and both the real and imaginary parts of the permittivity tensor yield two independent main components. The frequency dependent dielectric anisotropy is governed by permanent and induced dipole moments at low frequencies, and at the short wave side of the dispersion steps only by the induced dipole moment. From the observed dispersion curves of (epsilon) (parallel) and (epsilon) (perpendicular) we could show experimentally that the dielectric anisotropy (Delta) (epsilon) equals ((epsilon) (perpendicular) - (epsilon) (perpendicular)) of 4-n-pentyl-4'-cyanobiphenyl changes its sign twice over the frequency range covered by our experiments. The static dielectric anisotropy, as well as the optical anisotropy are positive, therefore this behavior should be expected. The change of sign in (Delta) (epsilon) would imply that the nematic director will align parallel to the external electric field in the low and high frequency limits, whereas it orients perpendicularly to the field at some intermediate frequency range.

Mechanism of dielectric of the thermotropic liquid crystal molecules is discussed on the basis of broadband dielectric spectra. Using the Nordio-Rigatti-Segre model some theoretical values are calculated and compared with the experiment.

Polar-dependent deformation of NLC in the region of the pore of the structure Metal-Dielectric-NLC-Metal is investigate. It is shown that polar-dependent character of deformation is due to charge polarization and injection processes. The monopolar current value is about 10^-11- 10^-13A. The selective charge accumulation induced coated film brings about a homeotropic transition or stabilization of planar oriented nematic 5CB respectively. It is shown that the NLC method tests the through like pores only.

Detailed frequency dispersion study of proton spin-lattice relaxation times (T₁) with Larmor frequency over a wide range using FCNMR technique has been carried out on the binary mixture of 4-Cyanophenyl-4'-octylbenzoate and 4- Cyanobiphenyl-4' (7BCB), exhibiting induced smectic island. The data were analyzed using a composite molecular dynamic model incorporating the different known mechanisms for the spin relaxation. The T₁ dispersion in 8CN is essentially dominated by the order director fluctuations (ODF) in the nematic phase, while in 7BCBC they are governed exclusively by the self-diffusion of the molecules. The intermediate nematic phases show a gradual change between the two different scenarios. The formation of smectic phases are accomplished by the near freezing out of the ODF contribution, and sudden slowing down of the diffusion. There orientations show a variation in their correlation times in the nematic phases over these relative concentrations, but show dramatic decrease in correlation times on the formation of layered structures.

Complex dielectric permittivity measurements performed for right handed (s) 4-(2-methylbutyl)-4'-cyanobiphenyl (CB15) in frequencies from 0.1Hz till 100kHz are presented. The phase sequence observed on cooling differs form that observed on heating: on cooling only an isotropic liquid and a glassy phase have been observed while on heating the glass transforms to a viscous liquid that crystallizes around 245K. On further heating the crystal melts to form the isotropic liquid at about 280 K. Temperature dependence of relaxation time is found to be of the Vogel-Fulcher-Tamman type.

A deuteron NMR study of the 8CB liquid crystal confined to the controlled pore glass matrix is presented. The theoretical analysis based on the phenomenological Landau - de Gennes type description predicts a strong influence of the pore curvature on the confined 8CB smectic ordering and almost none on its nematic ordering, in good agreement with experiment.

We present a new type of effective photoregulation of the LC orientation on an aligning surface through light action upon the liquid crystal bulk. The illumination of an azo- containing LC bulk with polarized light is found to induce both stable high-resolution alignment onto the rigid surface and dynamic sliding of the director over the surface. Typical times of the director sliding over the aligning surface are of the order of 1 ms. Both effects are characterized by extremely small light intensities and seem to be very promising for the development of optical devices for information processing and high density information storage. Light-induced surface memory effects are also observed in these system as a consequence of induced anchoring of the molecular director. This technique has been applied to record both stationary and dynamic holograms with a spatial resolution of 7 micrometers . The surface memory effects have been applied to record both binary and gray scale images. As compared to other methods used in these materials the highest sensitivity and spatial resolution can be achieved: energy densities as low as 10^-1J/cm² were sufficient to write gratings with a resolution better than 100 lines/mm.

In this work sinusoidal diffraction gratings with a range of pitches and amplitudes are used to algin nematic liquid crystal layers in a twisted homogeneous configuration. The grating profiles are accurately characterized using optical surface plasmon polariton spectroscopy which then allows a calculation of the anchoring energy as predicted by the simple Berreman expression. The experimental Rapini-Papoular anchoring energy is also obtained by a measurement of the director twist away from the alignment direction at room temperature. A linear relationship is found between the two anchoring energies except when it falls below 4 X 10^-7Jm^-2. Noticeably, the correlation between the two theories is hot unity, if room temperature elastic constants are used in the calculation. This apparent inconsistency is explained if the effect of surface memory on the system is considered. Indeed if elastic constant, corresponding to a higher temperature, at which surface memory effects are absent, are used in the Berreman expression, good agreement between the predicted and experimentally measured energies is found.

Optical measurements of the retardation between ordinary and extraordinary wave in the liquid crystalline retarder suggest that an interfacial layer between substrate and liquid crystal (LC) exists. The theoretical model that allows one to describe the presence of such a layer has been constructed and illustrated, for simplicity, in model with neglected elastic anistropy. It turns out to be quite enough to fit an experimental data of phase retardation to obtain values of the pretilt angle and anchoring energy. Experimental results confirm that near threshold voltage value the homogeneous LC layer is deformed in more complicated way that his one describe in one elastic constant model. For higher voltages such a model seems to be proper one because of the LC layer deformation is mostly bend like kind.

In this paper there is demonstrated that the threshold external field magnitudes for Freedericksz transition in nematic liquid crystals can be considered in the form of the boundary eigenvalue problem for differential operator d²/dx² with different boundary conditions. Three case have been investigated due to three boundary conditions a the planar nematics layer surfaces: strong anchoring of molecules parallel to the surface, week anchoring of molecules at the surface and strong anchoring of molecules tilted to the surface.

An equation of motion for the second order alignment tensor, including the influence of electromagnetic fields is derived. The starting point are the mesoscopic balance equations of mass and of angular momentum. A constitutive equation on the mesoscopic level is discussed. The two balance equations together with the constitutive equation yield a Fokker-Planck type equation of motion for the ODF. This finally leads to a nonlinear partial differential equation for the alignment tensor.

The dynamics of the field induced 1D twist deformation in weakly anchored nematic layers was investigated by means of numerical simulation. The rise time constants and the decay time constants, characteristics for the onset and for the decay of the deformation, respectively, were determined. The time of delay, which had passed before the decay started, was revealed in the case of finite anchoring. For weaker anchoring, the time of delay and the decay time constant were longer. The onset of the deformation was slower when the anchoring was weaker, provided that the actual field strength to the threshold field strength ratio was fixed.

The shear flow induced deformation of the planar long pitch flow-aligning cholesteric was modeled numerically. Three pitch-to-thickness ratios, with the midplane director perpendicular to the plane of shear, were considered.Unwinding of the cholesteric helix due to the flow alignment was found. A threshold character of this process was revealed. At high stress, the director in the prevailing part of the layer was oriented at the flow- aligning angle. The transverse component of the flow was always present.

The simple shear flow induced deformations of the flow- aligning nematic are modeled numerically. The director distributions in the sheared layer are calculated for various surface orientations. The director coming out of the shear plane, which has been predicted earlier, is confirmed. The results show, that the coming out of the shear plane should not be treated as a separate effect appearing during the flow, but rather as a way, in which the usual flow aligned structure is achieved. This way is realized, when peculiar boundary conditions are imposed and when the relatively small twist elastic constant makes it energetically preferable.

Optical and dielectric properties of two liquid crystals, the well-known PCB and the equimolar mixture of Demus esters, have been investigated. A semi-empirical method to determine the liquid crystal-substrate interaction potential has been employed. By applying the self-consistent director field method and the effective electric permittivity measurements the liquid crystal-substrate interaction potential values have been estimated.

Surface driven reorientation effects in a nematic liquid crystal cell caused by light-induced changes of the anchoring energy were studied. The threshold director reorientation takes place for the perpendicular directions of the reference and light-induced easy axes. The transition was found to be close to the second-order one revealing the critical increase of the director thermal fluctuations in the vicinity of the transition point. The mentioned effects were experimentally studied in cells of liquid crystal 5CB aligned by the photosensitive azo-containing polymer layer.

The stability of the nematic director field under applied magnetic fields is studied using continuum theory. The stability analysis of two order parameter potentials allows the study of the influence of the external field on the development of static periodic distortions in the director field. The case of oblique applied fields is studied. In the frame of a phase transition analogy, where the angle of the field with respect to the unperturbed director plays the role of the external parameter, phase diagrams are shown for the critical angle for the director transition from the homogeneous to the distorted state, as a function of the Frank elastic anisotropy.

Using a surface force balance, the orientation of a nematic liquid crystal confined between mica surfaces, and its response to shear under extreme confinement was examined. Slow transitions from a planar twisted to a planar orientation were observed in certain conditions. We propose that these are associated with anchoring transitions.