The induction of orientational order close to a surface has been observed for an isotropic diacetylene compound under pulsed laser illumination into its absorption band. The value of the induced birefringence is proportional to the square of the intensity of the absorbed light. The direction of the photoinduced optical axis is defined both by the substrate surface and the light polarization vector. The observed phenomenon is explained by photoinduction of fluctuations of the nematic order in the vicinity of the surface and reorientation of these fluctuations under the polarized light illumination.

In this paper we give a short review of some recent theoretical results on the interfacial and surface properties of nematic liquid crystals (NLCs). By using a phenomenological and a molecular model, we show that the surface free energy of nematic liquid crystals contains new specific elastic and geometric terms. Furthermore we show that surface elastic terms that depend on the director derivative along the normal to the interface cannot enter a macroscopic theory of NLCs. Then, we propose a new expression of the surface free energy F_s that does not contain normal director derivatives. F_s contains four independent contributions: a classical anchoring energy, two new geometric surface terms that depend on the two local curvature radii and an elastic term formally equivalent to the classical K₂₄ term. The new free energy is bounded from below and always admits a minimizing director field. All these surface terms can be measured by making suitable experiments on NLCs in spherical or cylindrical cavities.

The surface tension of liquid crystals at the free surface has been found experimentally to exhibit intriguing behavior in the neighborhood of the nematic-isotropic transition temperature T_NI. We discuss general features of the relation between wetting properties and temperature dependence of the free surface tension close to T_NI. Different wetting properties are expected to yield a varied assortment of surface tension characteristics. In order to supplement and extend these arguments, we have analyzed the surface tension using a microscopic density functional model. In this approach anisotropic volume exclusion effects are neglected, isolating instead the effect on the surface tension of the orientationally coupled Lennard-Jones potential. Wetting properties are sensitive to the different spherical harmonic components of this potential, and thus the model exhibits a rich array of surface tension behaviors, of which we give a brief overview. The principal new result of the calculations we have performed, summarized here, is the appearance of a pre-transitional surface tension minimum which is seen in many experimental studies. This is related to anomalously high sub- surface order.

Observations of the nematic LCs alignment on the surface of amorphous hydrogenated carbon (a-C:H) layers are reported. These layers were prepared from toluene by plasma-activated chemical vapors deposition process. It was found that the surface of as prepared films had produced parallel alignment of alkylcyanobiphenyls LC mixture with positive dielectric anisotropy. Thea-C:H layers surface treated by means of the oxygen plasma could orientate the same LCs homeotropically. It was established the dependencies of the pretilt angle of LCs on the glow discharge power during deposition of a-C:H layers and the oxygen plasma treatment dose of their surface after the preparation. A simple model to explain these observations is presented.

The dependencies of a surface topography of the obliquely deposited layers of ceric oxide (CeO₂) films and amorphous hydrogenated carbon (a-C:H) on an incident angle of a vapor stream have been studied by electron microscopy. The dependence of the alignment of nematic LCs onto CeO₂ layers surface on the relief geometry which correlated with incident angles in interval 60 degree(s) - 85 degree(s) was observed. The surface structure of a-C:H layers depends only substrate surface relief. The smooth surface of a-C:H secures stable parallel alignment nematic LCs independently of incident angles.

The paper presents the results of theoretical and experimental investigations of static deformations in homeotropic Nematic Liquid Crystal layers, taken place in a spatially nonuniform radial symmetric electric field. The calculations take into account both dielectric and flexoelectric torques. The nonuniform electric field is created by a charge disk of a various size.

A new field-off technique for measuring polar anchoring energy of a nematic liquid crystal on a solid surface is offered. The technique is based on estimating anchoring strength from the experimental conditions under which symmetrical configuration of nematic director field occurs in wedge cells with the boundary conditions asymmetrical in the anchoring strength and easy axis orientation. The presence of symmetry elements is determined from the relation between the LC cell transmittances for various polarized components of incident light. The feasibility of the technique is proved by numerical simulation.

A new optical technique allowing one to obtain quantitative information on the director field configuration in LC layers with 1D unhomogeneity of the general form is offered. The numerical simulation results demonstrating the potentialities of the offered optical technique are given.

In the usual continuum theory the simple dynamic model is considered for an approximate description director transitions in a nematic layer. Influence of all the director pretilt, the anchoring, and the viscosity at surfaces on the director configuration can be investigated using this model.

Spontaneous in-plane bidimensional stripes are predicted to appear in thin films of tilted smectic liquid crystals, due to flexopolarization, provided the flexoelectric coefficients are great enough, as in several smectic C's. The two periodicities arise in orthogonal directions. In the presence of free ions, the charge distributions becomes also modulated in-plane, partially masking the direct flexopolarization influence. Both effective periods are of the order of 10 micrometers . The optical observations were performed on mixtures of trans-4-(trans-4'-n- amylcyclohexyl) cyclohexanecarboxylic acid (CCH) and of 4-(trans-4'-n-amylcyclohexyl) benzoic acid (PCH). Both pure compounds exhibit only a nematic phase, the first between 224 degree(s)C and 243 degree(s)C, and the second one between 180 degree(s)C and 265 degree(s)C. The experimental data are consistent with the present model, suggesting that, for certain CCH/PCH ratios less than 30%, a tilted smectic phase is nucleated close to the melting point.

The stimulation of electrohydrodynamic instability and the focal conic (FC) to homeotropic (H) transition (F-H) v.v. in S_A phase liquid crystals (LC) have been investigated. This processes are the reason of FC and H stable structure formation with maximum and minimum light scattering respectively. Data indicate that the media peculiarities and mechanism of the electrooptical effects enable to stimulate the structure transition by the anisotropy of LC cell surface relief. The relief anisotropy is the equidistant rectangular network of modulated layer disturbances similar to a square one is more energy advantageous. It determines the decreasing of the threshold voltage and LC response time. The obtained results will enable us to solve the boundary task by the constructive-technological methods of the LC display development having the regular matrix pixels and using the principle of the control field light scattering. It is possible to fabricate LC display without the alignment layers having the contrast over 40:1, the optical reaction time less than 50 ms and threshold less than 50 V.

In work we discovered a surface electrooptical effect for thixotropic layers. It is an appearance of the surface microrelief which dues to a dynamic scattering of light caused by its relief-phase modulation by the formed surface microrelief. Temperature range of this effect existence is very wide (from -80 degree(s) to +80 degree(s)C). Latter is distinguished from limit range of dynamic scattering effects for liquid crystal (from units to tens degrees). The aim of this paper is to investigate the nature of effect mentioned above and to consider its uses for different branches.

The non-mesogenous solid-state substrate movement in normal direction can induce the liquid crystal phase transformation of the structure-texture type. The phase transformation results in the morphological interphase boundary instability and leads to the non-mesogenous crystal (NMC) growth shapes variety, including the fractal structures. The orientation influence of NMC substrate is estimated by the optical unipolar analysis of LC textures.

We report the effect of Asymmetry of Bragg reflective band of Cholesteric Liquid CRystal caused by the excited doping molecules of 4-phenilchalkon. Two possible reasons giving the explanation of the effect are nonuniform concentration of khalkon molecules in the bulk and absorption of the molecules on the inner surfaces of the cells. The influence of nonuniform variations of pitch step and the refractive index modulation on the shape of Bragg band are studied numerically. It has been shown that the variations of pitch step are probably the reason of asymmetry of the Bragg band. The used model is based on solving the equations of the Theory of Dynamical Reflection for the wave propagates along the cholesteric director axis.

New dynamical aspects have been investigated in the flexoelectrically excited angular waves of a nematic liquid crystal by means of a modulation ellipsometry technique. At low frequency (f < 1 Hz) the gradient flexoelectric torque dominates and causes an out of phase electrooptical effect. At high frequency (f > 1 kHz), the surface friction is responsible for a new dynamical behavior. The surface viscosity is evaluated to be 3 (DOT) 10^-5 erg(DOT)s/cm².

Atomic Force Microscope images of obliquely evaporated SiO_x onto indium-tin-oxide (ITO) thin film electrodes as used in liquid crystal displays show no pronounced regular structure of the SiO_x thin films as used in theoretical approaches to explain the alignment of liquid crystals. Subsequent investigation of the morphology of the ITO surface using scanning tunneling microscopy shows that this surface is rough on many scales and shows step heights as large as 0.1 micrometers . Based on these observations we suggest two mechanisms which might be responsible for the liquid crystal alignment and methods for improving alignment.

We call the bistabifity of ferroelectric liquid crystal (FLC) cells as the surface bistability (SB), if the dispersion part of anchoring energy is responsible for this type of bistabiity. SB was predicted theoretically [1] and investigated experimentally [2-4] .It was shown, that SB there exists in SSFLC cells possessing the bookshelf structure of smectic C layers [2] and SB there exists only in limited region of multidimensional space of cell and driving voltage parameters [3]. Anchoring energy of FLC with solid surface for SB structures is [4]: 102 iO erg / cm2 On the other hand there exists the volume bistability (VB), which have been observed by us recently in thick (15 mkm and more) layers of new FLC compositions [5].VB is a special phenomenon caused only with stereo chemical nature of the FLC composition and quite independent upon surfaces. In this work we would try: to found the physical principle for experimental measurement of an average free energy density of ferroelectrics, -to describe manifestations for both SB and VB, - to compare SB and VB from point of view their free energy parameters.

Fourier transform infrared spectroscopy of a ferroelectric liquid-crystalline material: 4-(3)-(S)- methyl-2-(S)-chloropentanoyloxy-4'-octyloxy-biphenyl has been investigated in the wavenumber range 450 - 4000 cm^-1 for various temperatures and as a function of direct bias voltage in its SmC^* phase. Samples prepared in both homeotropic and homogeneous alignments have been studied. The order parameter was calculated for several isolated IR vibrations which are characteristic of different parts and orientations of molecules. The dependence of the molecular tilt angle on direct bias voltage and temperature has similar characteristics to those obtained from electro-optic measurements.

The experimental investigation of the influence of electric field on luminescence of thin liquid crystal layers are presented. It is shown that the observed luminescence quenching is nearsurface phenomena dye to the exiton nature of liquid crystal luminescence.

The influence of the quartz-substrate surface on the orientational arrangement in the NLC wall-adjacent layers in the thickness region that corresponds to the layer with excess (in comparison with the bulk) ordering--l < 0.1 (mu) was studied. The measurements of electronic spectra of the wedge-like 5CB samples with P- and H-orientation in the frequency region 30000 divided by 48000 cm^-1 were carried out. The experimental spectra were decomposed to elementary bands and the thickness dependence of their parameters was discussed.

Spatial light modulators using an amorphous silicon semiconductor and p-i-n diode configuration are fabricated with nematic liquid crystal. The performance characteristics of the devices are compared.

Surface layers of a number of polymers have been studied with the help of the method of birefringence of light passing through the film with the angle of incidence other than normal. Two types of orientational order of molecular chain fragments relative to film surface have been found: predominantly parallel and predominantly normal. It appeared that surface layer width can reach considerable value (up to 0.6 mm). It has been shown that thermoprocessing plays an important role in formation of physical properties gradient in polymeric substance near the surface.

The statistical properties: orientation correlation function, mean-square dimensions and mean susceptibility are calculated for polymer chains ordering at surface. A correspondence of properties and character of the phase transitions in the 2D polymer systems with effects of volume and orientational interactions is discussed.

The phase transitions from isotropic into ordered state in the 2D polymer systems consisting of chains with fixed mean-square length of segments and those of chains of rigid elements are considered. Short and long-range orientational order in these systems are compared both by the self-consistent field approach and the multichain models.

The polyvinylcinnamate modified by the partial substitution of side chains for stearoyl fragments has been investigated. An oblique liquid crystal alignment with pretilt angle values controlled by the concentration of the stearoyl groups is obtained. The double degeneracy of an easy axis induced by polarized-light-irradiation technique is also verified.

Achievement of predetermined LC alignment on a substrate surface is a very difficult physicotechnical problem which is not yet perfectly understood, despite a great interest of researchers to it. In this paper we report some experimental results of the investigation of nematic and smectic LC alignment on the surface of a number of polyimide compositions.

Hysteresis characteristics of volt-contrast curve of polymer dispersed cholesteric liquid crystal films have been studied as a function of temperature, time, voltage, material structure and composition. Material under study allows thermocontact and laser-addressed information recording with gray scale in both normal and reverse scattering mode. Recorded information can readily be erased by electric field on/off.

The orientational ordering of nematic (5CB) droplets with the bipolar director-field configuration, embedded in the uniaxially stretched polyvinyl alcohol matrix, is studied by polarizing optical microscopy. It is found that at small matrix deformations each bipolar structure is captured by the surface of the droplet cavity but, if the droplet non-sphericity further increases, there comes a point where the droplet abruptly reorients parallel to the long cavity axis. The measurements of the orientational distribution function testify the threshold nature of the bipolar droplet's ordering process. The heating of the slightly elongated polymer matrix above its glass transition temperature is found to eliminate the captured structures and produces the irreversible uniaxial orientation of the sample. The obtained information is analyzed in terms of three models taking into account the microrelief of the droplet surface, the ordered organization of polymer molecules at the droplet boundary, and the initial non- sphericity of droplet cavities, respectively. It is inferred that the formation of the supramolecular polymer structure at the matrix/droplet interface during the matrix curing process and its changes with stretching and heating are the governing factors responsible for the experimentally observed phenomena.

Orientational electrooptic effects in liquid crystals (LC) have found wide practical use in information display devices. Obvious advantage of liquid crystals based on `twist effect' has been universally recognized. This advantage is mainly connected with the fact that in the case of normal incidence of light beam the geometry of `twist' elements is not characterized by any phenomena related to dispersion of refractive index, and that such LCs cope well with controlling white light beams. The use of orientational effects associated with the changing of birefringence is limited by a more rigid fixing of modulation characteristics to the light wavelength. Using of thin LC layers allows to take away this limitation.

The reflection spectra of cholesteric liquid crystals dispersed in polymer and comprising pyrimidine dopes are investigated in the entire temperature range of the mesophase existence. One or several oxyphenyl substituents in an ortho position implemented into a pyrimidine system induce the second reflection region. The reflection curves for different wavelengths corresponding to regions I and II merge with temperature. Thermodynamically equilibrium states of polymer-dispersed cholesterics under the influence of polar pyrimidine dopes are considered. The pyrimidine effect is modulated by the orientational near-surface potential. The existence of two space regions of a spherical droplet with different helix pitches is validated. The natural helix pitch is retained inside the droplet while a new pyrimidine-induced pitch is formed in a layer close to the droplet surface. The results obtained describe the existence of two reflection regions and the temperature behavior of the helix pitch.

Various types of polarizer-free light modulators based on polymer dispersed ferroelectric liquid crystals are discussed. Efficiency of light-modulation has been studied for different temperatures and values of the applied voltage.

Theoretical analysis of shaping NLC layer on the surface bearing energy pattern is presented. On the basis of the balance of surface energy and layer elasticity of elongation energy the form of the layer surface is determined. The interference picture on the layer thickness and shape is analyzed. By means of mathematical methods of communication theory the surface information bulk is achieved where the layer is considered as the communication channel to transfer the energy pattern from the substrate. In the course the thermal noise is taken into account. On that basis the limit spatial resolution of the layer and the method sensibility is determined.

The thin layer of homogeneously oriented nematic liquid crystal (NLC) applied on the optical quality solid crystal surface as a free film may visualize the images of structural defects through a polarizing microscope. On this basis a new non destructive method to study surfaces of different materials has been developed. A new application area of the NLC technique for investigation of structural inhomogeneities in solid crystals is discussed.

The possibility of the real time X-ray-to-visible image conversion using intrinsic photoeffect in semiconductors and hybrid field effect in nematic liquid crystals is shown. The possible application areas are discussed, and the peculiarities connected with optical information processing in this system, are considered.

Effects of orientation in nematic liquid crystal (LC) at non-uniform electric field can be used to create new optical devices. A non-uniform field causes a deformation of nematic director and a radial symmetrical distribution of a refractive index is obtained. This LC-cell possesses the lens properties. The optical properties of LC-microlens with homeotropical alignment of nematic have been researched. The diverging property has been obtained in this structure. The LC-microlens focal length--voltage dependence has been investigated.

The effect of various alignment films based on both oxides and polymers on dynamic characteristics of light-addressed nematic liquid crystal spatial light modulators (SLM) has been investigated. The mechanism based on an internal p-i-n diode model has been proposed to interpret an increase in a speed of the SLM using polymer alignment films.