PDLC composites containing elongated ellipsoidal or flat liquid crystal droplets have been prepared by three different methods depending on properties of polymer matrix. The morphology of composites, i.e. concentration, size and shape of droplets have been changed during the preparation process and optimized after studies of optical properties. The light scattering of PDLCs, especially the optical contrast ratio in on- and off states, selective light reflection in case of chiral nematics dispersed in polymer as well the polarization properties of PDLC systems containing elongated liquid crystal droplets have been studied.
The prospects of application of polymer-dispersed liquid crystals in information displays are discussed. The brief information regarding methods of preparation of such composites is given. The main electro-optical effects observed in different LC dispersed phases and the effect of PDLC morphology on their electro-optical properties are presented. The advantages and disadvantages of PDLC as materials for construction of different kinds of displays are discussed and the promising applications are shown.
The effect of preparation method and properties of components on the polymer-dispersed liquid crystal (PDLC) composite morphology is described. Three different methods of PDLC preparation -- encapsulation, solvent-induced phase separation and photopolymerization-induced phase separation have been studied. Especially designed nematic and chiral nematic mixtures have been used as liquid crystal (LC) materials fulfilling requirements for mutual solubility and refractive index matching of composite components. In all cases the effect of LC concentration and the rate of solidification of polymer binder has been analyzed. It has been confirmed that the mean size of LC droplets is approximately proportional to the LC concentration and inversely proportional to solidification rate. The shape of droplets is usually close to spherical but using special methods one can obtain ellipsoidal droplets. The effect of morphology on electro- and thermooptical properties of obtained PDLC systems has been studied. The correlation between PDLC morphology and possible applications is discussed.
In this work we present the results on synthesis of sol-gel produced compounds containing SiO2 and MgO in different stoichiometric proportions. Tetraethoxy silane (TEOS), magnesium acetate, and dysprosium nitrate were used as precursors. After hydrolysis of TEOS in ethanol solution the other precursors dissolved in ethanol were added. After several hours the gelation process occurred, and transparent glass was formed. Subsequent heating at temperatures up to 1050°C led to formation of compounds containing SiO2 and MgO: enstatite and forsterite. We checked the formation of relevant phases by means of X-ray powder diffraction. Thermoluminescent properties of the obtained compounds were checked after doping them with dysprosium ions. Linear response of thermoluminescent properties on gamma irradiation was found, but the sensitivity of phosphors obtained in this way was rather moderate comparing with other well known thermoluminescent phosphors.
The essential properties of polymer-dispersed liquid crystals are described. The main attention is paid to the influence of system morphology on electro-optical properties of nematic-containing systems. The thermo-optical properties of dispersed chiral nematics are presented. Electro-optical switching in systems containing ferro- and antiferroelectric liquid crystal phases is shown. The selected applications of the discussed systems are presented, including electrically switchable windows, fast light modulators, sensors, fiber-optic devices and presentations for teaching physics.
The liquid crystal display dashboard for polish gliders PW-5 and PW-6 have been presented. The measuring flight parameters system and electronic scheme of the glider have been proposed, developed and tested. Laboratory investigations of the board flight parameters and their compatibility with standards have been described.
The aim of our work was precise dielectric permittivity measurements of compound: (See paper for formula) Results of spontaneous polarization, tilt angle in the SmC* phase and first dielectric permittivity measurements of all phases of this compound were presented by us. The phase transition to SmC* phase is characterized by strong maximum for low frequencies and minimum for high frequencies of dielectric responses. Thus in 118 degree(s)C for our compound one can see phase transition to SmC* phase2. From the linear temperature dependences of relaxation frequency fR and the inverse dielectric strength 1/Δε(perpendicular) obtained by fitting experimental values ε' and ε" to Cole-Cole equation, the SmC(α )* (in the narrow temperature regions) is detected due to the change of the slope. The relaxation process observed in the SmC(α )* phase is strongly modified under bias, thus it is probably connected with the helicity of SmC(α )* e.g. ferroelectric-like structure of this phase.
An application of thermosensitive PDLCs containing chiral nematics in general physics course is described. Several examples of students' exercises and lecture demonstrations concerning heat effects are presented.
An application of thermographic methods in pulmonological diagnostics in children is presented. Basic information concerning liquid crystal contact thermography is given. Diagnostic procedures and essential conclusions are described.
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.
The construction of the fiber-optic sensor for the recognition of perturbations and results of its studies are presented. As a sensor head, the sample of few-mode optical fiber is used. Changes of intermodal interference condition, caused by external perturbation, have generated changes of output speckle pattern. This output has been concerned as an intensity image and diffraction method has been applied for its recognition. The image feature extraction has been achieved by applying a computer-generated hologram in the Fourier plane of an output image. A size of ring and wedge generated by this hologram has been optimized by using the rough set theory. Then, a artificial neural network has been used to recognize the external perturbation without a necessary of troublesome analysis of intermode interactions. An additional advantage of this solution is the possibility to train the network to eliminate slow environmental perturbations.
Present paper contains results of studies on TN LC mixture containing black dichroic dye. The effect of dye on temperature dependence of LC order parameter and optical anisotropy, is discussed. Contrast coefficients and transmission in on-site at room temperature are presented.
Present paper contains results of studies on TN LC mixture containing black dichroic dye. The general information concerning a principle of action of TN display with dye is presented. The effect of dye on temperature dependence of LC order parameter, optical anisotropy and dielectric properties is discussed. Transmissive characteristics of a display for different dye concentration are given. Contrast coefficients and transmission in on-state at room temperature are presented.
In the present paper definitions, procedures and measurements set-ups for characterization of LCDs are discussed. As the effect standardization of LCD electro- optical properties has been improved.
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 SA1-N* phase transition.
Liquid-crystal thermography has been applied to estimate results of skin prick tests for children. Over 30 children chosen for tests due to allergy or other diseases have been examined. A new kind of thermographic foils containing chiral nematics has been applied.
The present state of knowledge in the field of polymer- dispersed liquid crystals (PDLC) is presented.The essential information concerning methods of PDLC preparation and their physical properties is given. The effect of material properties of a polymer and a liquid crystal, including different phases, on the electro-optical behavior of PDLC is discussed. The possibilities of an application of PDLC structures for information display, modulation of light beam and sensor devices are considered.
The analysis of the optimization of negative image twisted nematic LCD is presented. Theoretical considerations are confirmed by experimental results. The effect of material parameters and technology on the contrast ratio and display dynamics is given. The effect in TN display with black dye is presented.
Investigations of thermoluminescence of lithium tetraborate activated with Dy, Mn and Eu and calcium sulphate activated with Dy caused by irradiation have been described. Both kinds of materials may be used in military and accident dosimetry.
Liquid crystal composites, i.e., two phase polymer-liquid crystal systems, are very interesting from a scientific and application point of view. Amongst them the best known is PDLC (polymer dispersed liquid crystal) structure. In this material liquid crystal (LC) droplets, diameter of 0.1 - 10 micrometer are embedded in a polymer matrix. PDLC composites are used for construction of new information displays, image projectors and optical devices. In the presented work essential material requirements for PDLC are given from an application point of view. They concern mainly well-known electro-optical effect of electrically induced transmittance. The examples of experimental results are also presented.
A brief description of the basic optical and electro-optical effects observed in polymer-dispersed liquid crystals (PDLCs) is presented. Theoretical models of light scattering from such structures and measurement techniques of PDLC optical properties are included, based on which of the material properties of polymer and liquid crystal required for application are discussed. Special attention is paid to the methods for optimizing PDLC optical and electro-optical properties. Finally, the known and possible applications of PDLC optical properties are discussed.
The methods of creation of areas with different structural properties in one PDLC layer are described. It means that number, size, and shape of liquid crystal droplets, and also a director alignment, are different in particular areas of a polymer matrix. For this reason, optical and electro-optical properties of such a layer are unhomogeneous and an optical pattern may be obtained for the light passing through the layer. Possibilities of application of PDLC layers with structural pattern in optical devices are discussed.
The application of liquid crystal contact thermography for point skin tests used in allergology diagnostic has been studied. The effect of a concentration of histamine, adopted as the etalon substance, on observed temperature fields is presented. Obtained results have been confirmed by thermovision measurements. A correlation between studied method and visual estimation used until now is the best for temperature range observed as a blue color.
A permanent periodic structural grating has been formed in a PDLC layer. This structural pattern caused a diffraction of the incident light. The obtained structure has exhibited features of both amplitude and phase diffraction grating. Due to PDLC electro-optical properties, this grating is adjustable by electric field i.e., the grating type and the diffraction fringe number depends on applied field.
Reverse-mode PDLC, i.e. transmitting in off-state and scattering in on-state, has been studied. It has been found that such a structure may be obtained without special treatment, however, it exhibits low contrast ratio and high haze in off-state. For improvement of electro-optical parameters, especially designed LC mixture should be used.
Laboratory models of PDLC information displays have been developed. It is possible to replace conventional TN LCD diplays in certain applications by PDLC displays with a high unification of materials and technological instrumentation. Such PDLC displays may be useful especially for large dimension information boards.
General rules for choosing LC mixtures for PDLC devices are given. Several methods used for adjustment of LC properties are presented. An example of LC material optimization in case of PDLC information display is given.
Prick tests are commonly used in allergy diagnosis but in some cases obtained results are difficult for objective interpretation. Application of liquid-crystal contact thermography improves this kind of diagnosis especially in the case of colored or sick skin.
Thermally induced phase separation of liquid crystal and polymer is one of the promising methods of polymer dispersed liquid crystal (PDLC) preparation. In this contribution general rules of choosing the proper polymer which fulfill all requirements are presented.
A possibility of applying poly(vinyl cyclohexanal) to polymer dispersed liquid crystals (PDLC) by thermally induced phase separation is presented. Obtained layers exhibit very good adhesion to glass and satisfactory electro-optical characteristics. The main disadvantage of this material is a complicated preparation of PDLC.
Temperatures of phase transitions in gamma irradiated mesogens decrease with absorbed dose due to the introduction of non-mesogenic products of radiolytic destruction. This effect may be described in terms of lattice model using geometric shapes of mesogen and admixture. The results for cholesterol nonanoate are presented.
An overview of preparation methods, physical principles, main properties, present and possible applications of polymer dispersed liquid crystals is presented. Special attention is paid to polymer dispersed chiral smectic liquid crystals.
The cholesteric liquid crystal (CLC) layers show circular dichroism and thus they can be used in circular optical polarizers. The paper includes the analysis of conditions which the CLC material -for such a polarizer should fulfil. Cholesteric materials for circular polarizers of Nd glass laser radiation were selected. The dependence 0-F the CLC layers transmission on its temperature and thickness and on the radiation power density was investigated. Polarization properties of the CLC layers were investigated too. The optical quality of a model of liqud crystal polarizer was also researched.
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