Search

In this study, a novel light switch was developed by integrating polymer dispersion liquid crystals (PDLC) and polymer-stabilised cholesteric liquid crystals (PSCLC), leveraging the infrared shielding properties of these two liquid crystal films. The optimal formulation for each layer of the liquid crystal structure was investigated. Subsequently, the effects of light intensity, high temperature, and humidity on the performance of the light switch were examined. This new light switch can be selectively driven layer by layer at room temperature, achieving three states: the off state, PDLC layer-driven state, and full-driven (on state). This functionality serves the purpose of electrogenerated temperature control. Samples under optimal conditions exhibited a 31% enhancement in infrared shielding compared to a single-layer PDLC film. Moreover, the IR shielding rate could be adjusted according to the voltage applied, realising an intelligent temperature-control effect. The results of this study suggest that such bilayer liquid crystal structures hold significant potential for application in electro-optical devices and smart curtain systems. [ABSTRACT FROM AUTHOR]

The societal impact of liquid crystals (LCs) in electrooptical displays arrived after decades of research involving molecular-level design of LCs and their alignment layers, and elucidation of LC electrooptical phenomena at device scales. The anisotropic optical, mechanical and dielectric properties of LCs used in displays also make LCs remarkable amplifiers of their interactions with chemical and biological species, thus opening up the possibility that LCs may play an influential role in a data-driven society that depends on information coming from sensors. In this article, we describe ongoing efforts to design LC systems tailored for chemical and biological sensing, efforts that mirror the challenges and opportunities in LC design and alignment tackled several decades ago during development of LC electrooptical displays. Now, however, traditional design approaches based on structure–property relationships are being supplemented by data-driven methods such as machine learning. Recent studies also show that computational chemistry can greatly increase the rate of discovery of chemically responsive LC systems. Additionally, non-equilibrium states of LCs are being revealed to be useful for design of biological sensors and more complex autonomous systems that integrate self-regulated actuation along with sensing. These topics and others are addressed in this article with the aim of highlighting approaches and goals for future research that will realise the full potential of LC-based sensors. [ABSTRACT FROM AUTHOR]

Purpose: To study the accommodative dynamics for predictable and unpredictable stimuli using manual and automated accommodative facility tests Materials and Methods: Seventeen young healthy subjects were tested monocularly in two consecutive sessions, using five different conditions. Two conditions replicated the conventional monocular accommodative facility tests for far and near distances, performed with manually held flippers. The other three conditions were automated and conducted using an electro-optical system and open-field autorefractor. Two of the three automated conditions replicated the predictable manual accommodative facility tests. The last automated condition was a hybrid approach using a novel method whereby far and near-accommodative-facility tests were randomly integrated into a single test of four unpredictable accommodative demands. Results: The within-subject standard deviations for far- and near-distance-accommodative reversals were (±1,±1) cycles per minute (cpm) for the manual flipper accommodative facility conditions and (±3, ±4) cpm for the automated conditions. The 95% limits of agreement between the manual and the automated conditions for far and near distances were poor: (−18, 12) and (−15, 3). During the hybrid unpredictable condition, the response time and accommodative response parameters were significantly (p < 0.05) larger for accommodation than disaccommodation responses for high accommodative demands only. The response times during the transitions 0.17/2.17 D and 0.50/4.50 D appeared to be indistinguishable between the hybrid unpredictable and the conventional predictable automated tests. Conclusions: The automated accommodative facility test does not agree with the manual flipper test results. Operator delays in flipping the lens may account for these differences. This novel test, using unpredictable stimuli, provides a more comprehensive examination of accommodative dynamics than conventional manual accommodative facility tests. Unexpectedly, the unpredictability of the stimulus did not to affect accommodation dynamics. Further studies are needed to evaluate the sensitivity of this novel hybrid technique on individuals with accommodative anomalies. [ABSTRACT FROM AUTHOR]

We report the first observation of light-induced director patterns formation in a planar liquid crystal (LC) cell with photosensitive chalcogenide film As20Se80. The angular patterns appear under the irradiation of the chalcogenide surface by Gaussian laser beam through the LC layer was observed. The experimental results are explained in terms of the transfer of heat from the chalcogenide film to the LC after the light absorption in the chalcogenide layer. Light-induced heating causes a change of the birefringence of the LC and, as a result, spatially modulated polarization state in the plane of the chalcogenide layer. Since the chalcogenide film is a photoaligning material, the spatial modulation of the light polarization leads to a formation of the spatially modulated easy orientation axis and the ring structure of the director in the cell. The model of liquid crystal gauss-shape prism was proposed also. We believe that this effect can be applied for development of different optical and electro-optical elements, such as beam shapers, micro-lenses, zone plates, etc. [ABSTRACT FROM AUTHOR]

Quercetin was subjected to a quantum-mechanical analysis and energetic and electro-optic parameters were evaluated. A solvatochromic study was used to estimate the dipole moment of quercetin in the excited state and to determine the angle between the dipole moments of this molecule in the electronic states responsible for the visible absorption band. The contribution of each type of intermolecular interactions to the total spectral shift experimentally recorded in quercetin solution was also established in this study. [ABSTRACT FROM PUBLISHER]

New functional multicomponent ferroelectric liquid crystalline mixtures have been designed while searching smart self-assembling materials with submicrometre periodicity of the helical structure responding definite demands for application in electro-optic devices and photonics that exploit the deformed helix ferroelectric effect. The resulting designed mixtures possess the paraelectric smectic A* and the tilted ferroelectric smectic C* phases over a very broad temperature range down below the room temperature. The mesomorphic, electro-optic and dielectric properties have been studied and discussed. The presence of a very stable enantiotropic ferroelectric smectic phase exhibiting almost temperature independent helical pitch within 150–250 nm range and reasonably high values of the tilt angle might allow these mixtures to be applicable for practical purposes. [ABSTRACT FROM AUTHOR]

The study reports a novel liquid crystal (LC) film that can be applied on the transmissive substrates or stuck on existing casement window to upgrade the shield. The shadow area and transmittance can be adjusted according to the condition of the outer sunshine. The window is energy saving for which maintains the transmittance after a once-off operation of pulse amplitude modulation (PAM) electric driving. Such a film can be applied in smart curtain, display frame edge and other transmissive electro-optical devices. [ABSTRACT FROM PUBLISHER]

We have prepared three different binary systems by mixing an achiral low viscous phenyl pyrimidine liquid crystalline SmC compound with three different orthoconic antiferroelectric analogous of (S)MHPOBC exhibiting SmA*-SmC*-SmCA* phase sequences. In these binary mixtures, ferroelectric and antiferroelectric phases were induced and their mesomorphic parameters (spontaneous polarization, response time, effective torsional viscosity, and anchoring energy coefficient) were determined by thermo-microscopic and electro-optical study. All the physical parameters show a nonadditive behavior with respect to the concentration of chiral mesogens due to strong dipole-dipole and/or intermolecular interactions between polar fluorinated chiral esters with heterocyclic phenyl pyrimidine compound. Interestingly the achiral mesogen reduces the response time of these binary mixtures at the cost of lower Ps. Therefore, these mixtures can be useful for high speed technological applications where low polarization, long pitch, and very fast switching ferro or anti-ferroelectric liquid crystal mixtures are desirable. [ABSTRACT FROM PUBLISHER]

Comprehensive maritime domain awareness includes detection, tracking, and identification of vessels, and we describe work concerned with the detection and tracking elements of this problem. Millions of maritime vessels operate without the means for their positions to be independently tracked, presenting a problem for safety and security of life at sea. To date, visible wavelength imaging from space has been of limited use for vessel detection and tracking due to poor area coverage provided by individual satellites. This situation is now changing. We present a survey of currently operating spacecraft carrying electro-optical imagers offering adequate imaging resolution and commercial data availability. We model the coverage provided by 54 satellites and 85 sensors over a target area to assess the value of these assets for space-based maritime domain awareness. The results show that useful levels of coverage can now be obtained through the collective observations of existing spacecraft, although on-board resources will limit the amount of imagery that can be acquired. The launch of large numbers of high-resolution imaging nanosatellites produced by private companies will improve this coverage, and the increasing capability of small satellite platforms offers the possibility of a dedicated Electro-Optical Space-Based Maritime Domain Awareness constellation that can realise the full benefit of the concept. We propose a cooperative approach, based on cloud computing and crowdsourcing philosophies, to the operation of the ground segment and the sharing and analysis of image data, to create an effective constellation of satellites and associated data handling infrastructure that can be used to enhance maritime security, and improve the safety of lives at sea. [ABSTRACT FROM PUBLISHER]

An electro-optic tunable device is fabricated by the incorporation of silica nanoparticles as a dopant into polymer-dispersed liquid crystal composite film followed by UV curing through polymerisation-induced phase separation process. These silica-modified fibrous aggregates of polydimethylsiloxane provide stability to the nematic liquid crystal molecules. The interaction between dispersed silica nanoparticles and modified polymer network improves the polymer/liquid crystal interface, which was successfully analysed through scanning electron microscopy. It also controlled the birefringence in nematic liquid crystal droplets and provided optical stability to the off-state (opaque) scattering of an electro-optic device. The electrical tuning of photoluminescence intensity during the stage triggering from ‘Switch OFF state’ to ‘Switch ON state’ shows dependence on the morphology of composite films. It can find out potential applications in electrically switchable shutters in display market. [ABSTRACT FROM AUTHOR]

This paper consists of two Parts. In the Part 1, we report the experimental results and considerations of the reduction of operation voltage and response time of narrow-gap TN(NTN)-LCDs embedded with the nanoparticles of hydrophobic Aerosil silica. While, in the Part 2, we give a report of the reduction of response time, especially τofffor the decay process of optically compensated tunable birefringence (OCTB)-mode LCD. [ABSTRACT FROM PUBLISHER]

In this study, the chemical structures and physical property dependencies of the electro-optical properties were investigated in polymer-stabilized blue phase (BP) using the four kinds of 4-n-alkyloxy-4′-cyanobiphenyl (n-OCB) homologue chiral nematic LCs. It was confirmed that the optical response time and Kerr coefficient in polymer-stabilized BP was varied with the molecular parity as determined by the alkyl chain length of then-OCB homologue chiral nematic LC mixtures. [ABSTRACT FROM PUBLISHER]

A tunable plasmonic directional coupler is proposed based on the electro-optical control of a nematic liquid-crystal layer placed above two side-coupled gold stripe waveguides. It is shown that by proper adjustment of the structural parameters and the control voltage, the coupling length of the structure and the effective modal index of the individual waveguides can be tuned, allowing for the design of electro-optical liquid-crystal plasmonic directional coupler switches. [ABSTRACT FROM PUBLISHER]

Experimental results on antiferroelectric liquid crystalline materials are presented using techniques such as dielectric and electro-optical measurements. A demixing phenomenon has been observed for compounds exhibiting the ferroelectric SmC* phase in their phase sequence. This phenomenon is interpreted within the framework of a thermodynamic study. Large temperature hysteresis during cooling and heating has been observed and is discussed. The results of dielectric spectroscopy and electro-optical properties suggest that thermal hysteresis is related to the demixing phenomenon. The effect of cell thickness and spontaneous polarisation on the temperature range of this phenomenon has also been investigated. [ABSTRACT FROM AUTHOR]

Four nematic mixturesA, B, CandD, comprising alkylphenylethylphenyl isothiocyanates, alkylcyclohexylphenylisothiocyanates, biphenyl and terphenyl derivatives, respectively, were prepared and their physical properties investigated, including birefringence, static permittivity, dielectric anisotropy, splay elastic constant and rotational and bulk viscosity. All the mixtures exhibited a broad nematic range (∼100°C), moderate birefringence (Δn∼0.23–0.26), positive dielectric anisotropy (Δε ∼ 8–10) and low rotational viscosity. The mixtures showed improved performance in birefringence and viscosity properties in comparison with the widely used commercial mixtureE7. As far as display performance is concerned, mixtureDwas found to be the most valuable. A comprehensive study of the usefulness of the biphenyl and terphenyl derivatives as dopants in mixtures has also been conducted with a view to improving their physical parameters to give faster electro-optical response times in liquid crystal display devices. Application of these mixtures is envisaged in high-speed photonics and liquid crystal display devices. [ABSTRACT FROM AUTHOR]

A liquid crystal (LC) alignment technique has been developed that allows local control of the polar pretilt angle over the range of 0–90°. This was achieved through the formation of a polymer network localised in the vicinity of the LC cell substrates. The network was formed as a result ofin situUV-induced polymerisation of a photo-reactive monomer added at concentrations of 0.5–1%. Localisation of the polymer network at the LC–substrate boundary was achieved by the application of a high voltage before polymerisation. The resultant pretilt angle was determined by the voltage applied during the polymerisation and/or the duration of the voltage application before the polymerisation step. The desired pretilt angle could be set over a small area of the sample, which allows the fabrication of LC devices with spatially variable optical retardation. Using this method we fabricated a converging lens, a bi-prism, and a phase diffraction grating with resolution greater than 50 lines mm−1. [ABSTRACT FROM AUTHOR]

This study focused on the performance of solution-processed multilayer polymer light-emitting diodes (PLEDs) with both the hole and electron transport layers using poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as an active layer. By insertion of both the hole and electron transport layers, improved emission and transient characteristics were achieved for the electro-optical conversion devices. For the multilayer device, the maximum current efficiency of 2.2 cd/A and the short response times of electroluminescence (ca. 30 ns) were achieved. [ABSTRACT FROM PUBLISHER]

A new 6-dialkylaminobenzimidazole nonlinear optical dye was synthesized in eight linear steps with an overall yield of 16%. [ABSTRACT FROM AUTHOR]

Reverse morphology polymer dispersed liquid crystal (PDLC) films are liquid crystal dispersions in a polymer network, whose voids and crevices are filled by liquid crystal. If they are prepared with homeotropic alignment, they can give rise to transparent electro-optical devices, which can be turned into an opaque state by application of a suitable electric field. They can be easily prepared by polymerisation of mixtures of liquid crystalline monomers and liquid crystals. In this paper we have doped reverse morphology PDLCs with increasing amounts of single-walled carbon nanotubes and investigated their effects on the morphology, electro-optical properties, and conductivity of the PDLC films. The influence of a different initial alignment of liquid crystal (homeotropic, homogeneous, and random) has also been studied. [ABSTRACT FROM AUTHOR]

Photonic crystals (PCs) have many potential applications because of their ability to control lightwave propagation. We have investigated a tunable ultrashort electro-optical power divider in two-dimensional PC structures. The power divider, composed of a dielectric cylinder in air, is studied by solving Maxwell's equations using the plane wave expansion method and finite-difference time-domain method. The power-splitting mechanism is analogous to that of conventional directional couplers, utilizing coupling between guided modes supported by line defect waveguides. To increase the coupling coefficient of the PC coupler, the radius of the rods between two waveguides is reduced. The switching mechanism is a change in the conductance in the coupling region between the waveguides and hence modulating the coupling coefficient, and eventually switching is achieved. Such a mechanism of wavelength multiplexing should open up a new application for designing components in photonic integrated circuits. [ABSTRACT FROM PUBLISHER]

Electrooptic cells containing two transparent graphene electrodes and a nematic liquid crystal are fabricated. Between crossed polarizers, the transmission of monochromatic light versus voltage shows the well-known maxima and minima that are characteristic of the Freedericksz transition. The peaks appear approximately at the same voltage as those of conventional test cells equipped with indium tin oxide electrodes. This indicates that the conductivity of the graphene layers is sufficiently high to replace indium tin oxide. However, microscopic studies reveal that the alignment of the liquid crystal is not perfect, yet. Means of improving the alignment are suggested. [ABSTRACT FROM AUTHOR]

In this study, we have investigated newly synthesised chiral smectic A (SmA*) liquid crystals (LCs) with a lactic acid structure with polarised optical microscopy (POM). We started cooling from the clear point until a SmA* phase emerged as the temperature dropped to the range 55.7-88.6°C. At this point, the alignment of the LC molecules resulted in a homeotropic texture. To take advantage of this characteristic, we then mixed the SmA* LC into a negative dielectric anisotropy nematic-type liquid crystal (NLC)/photo-curable acrylic pre-polymer mixture system (the NLC mixture system) with photo-induced vertical alignment, to realise the vertical alignment effect among the NLC molecules. This multi-component LC mixture system gave rise to a special, unknown twist grain boundary AX (TGBAX*) phase with rather broad temperature range, which maintained its helix structure even after crystallisation. In addition, we also utilised the electrical field induced molecular tilt effect (the electroclinic effect) within the SmA* LC to improve the response time of the LC device and gray-scale capability of the NLC mixture system. We further observed this multi-component LC mixture system after ultraviolet light irradiation treatment with POM, to investigate the alignment of the LC molecules, device display and electro-optical properties. [ABSTRACT FROM AUTHOR]

We compared the electrical characteristics of polymer, poly(N-vinylcarbazole) (PVK) and small molecule, 4,4'-N,N'-dicarbazole-biphenyl (CBP), N,N'-dicarbazolyl-3,5-benzene (mCP), as host material in white organic light-emitting diodes (OLEDs) fabricated by solution process. In order to obtain the white emission, iridium(III) bis(4,6-difluorophenylpyridinato)-picolinate) (Firpic) and iridium(III) bis(2-phenylquinoline)(acetylaceton) [Ir(pq)2acac] were used as blue and red emitting dopant, respectively. As a result, devices with PVK, CBP, and mCP have the max. luminous efficiencies of 10.5 cd/A, 9.8 cd/A, and 4.2 cd/A, respectively. [ABSTRACT FROM AUTHOR]

We have fabricated carbon nanotubes (CNTs) doped homogeneously aligned nematic liquid crystal cells driven by fringe-field switching and their electro-optic characteristics were investigated. The CNTs doped liquid crystal cell shows lower transmittance, higher driving voltage but faster response time than those in the pure liquid crystal cell. In addition, CNTs-doped liquid crystal cells as a function of the CNT length were investigated. This paper gives an explanation on difference in electro-optic characteristics of pure and CNT-doped LC in the FFS mode. [ABSTRACT FROM AUTHOR]

Orthoconic Antiferroelectric Liq. Cryst. (OAFLC) have been extensively studied due to their unique electrooptical properties [1,2]. Practical implementation of this kind of liquid crystalline medium experiences many obstacles including a number of parasitic effects deteriorating the electrooptical performance. In search for working OAFLC a mixture with the helical pitch longer than the typical cell gap was formulated. Using this mixture near perfect optical uniformity and excellent dark state at the zero electric field applied was obtained. The physical and structural properties of mixture are presented and their parameters are discussed. The electrooptical performance is presented and discussed. [ABSTRACT FROM AUTHOR]

Semi-Interpenetrating Polymer Network architecture containing either PEDOT or PProDOT-Me2 leads to interesting electrochromic devices (ECDs) without need of transparent conducting electrode. Upon applied potential between +1.2 V and -1.2 V these ECDs exhibit 30% contrast variation in the full visible range. Furthermore, the control of the PEDOT content up to 0.3 leads to semi IPN-based materials with interesting change in the reflective properties in the Near Infrared region. [ABSTRACT FROM AUTHOR]

Molecular structures and their relation to the mesogenic behavior as well as physical parameters of orthoconic antiferroelectric smectic phases formed by partially fluorinated esters are reviewed. New multicomponent mixtures with long pitch and their electrooptical performance are demonstrated. [ABSTRACT FROM AUTHOR]

Liquid crystal blue phases have a fluid lattice whose structure is stabilized by cubic defects. Blue phases, which are classified as BPIII, BPII and BPI observed on cooling, exist over a small temperature range (ca. 1 K) between isotropic and chiral nematic phases. Recently, we reported electro-optical switching with a response time of the order of 10-2 s for the BPIII exhibited by a polar chiral T-shaped compound. We describe molecular design of a liquid crystal stabilizing a blue phase III, and discuss electro-optical switching in the blue phase. [ABSTRACT FROM AUTHOR]

We examine the differences in electro-optical behavior of weakly polymer stabilized cholesteric liquid crystals (PSCLC) when formed using either a flood lit UV lamp, a flood lit UV laser, or a holographically patterned UV laser. Both samples formed with the UV laser exhibit symmetry in their dynamic electro-optical properties relative to the front and rear surface of the polymerized cell. These cells exhibit a reversible ∼100 nm blue shift tuning of the notch upon application of a field when the reflectivity is measured from either side. The UV lamp sample exhibits large differences in behavior when examined from the front or back relative to the direction of the polymerizing source. The front surface exhibits tuning of the notch while measurements from the back surface yield only the typical binary switching behavior of a CLC. The overall switching fields in flood lit UV laser and UV laser holographically patterned samples are also considerably lower. These differences are explained due to the presence of a strong polymer gradient across the cell gap in the UV lamp flood lit samples which is not present for the UV laser stabilized samples. We also present novel electro-optical results when these laser cured cells are examined in transmittance mode. Strong anchoring at the two surfaces causes a strong anisotropic local LC structure across the cell gap when a field is applied. The two local environments next to each surface act to strongly pin the CLC structure whereas within the bulk, ample reorientation of the LC molecules occurs. When probed in transmission, unusual fringe patterns which change with the strength of the applied field are observed. [ABSTRACT FROM AUTHOR]

A cellulose derivative/liquid crystal composite-type electro-optical cell using a commercial cholesteric liquid crystal (CLC) was investigated. The electro-optical properties of the system were examined, i.e. the dependence on applied voltage of the reflected wavelength and the minimum and maximum transmissions. A thin film of the CLC was dispersed with a cross-linked cellulose film of 25 µm thickness. In the voltage dependence of the reflected wavelength it was verified that there is a hysteresis in the reflected wavelength. The variation of the reflected wavelength with temperature was also determined. The results are analysed in the framework of similar systems described in the literature for CLC dispersed in a polymer matrix. [ABSTRACT FROM AUTHOR]

The thermal annealing process was proposed to purify the pixel regions of a liquid crystal (LC) cell with polymer walls. This technique, based on thermal-induced phase separation, successfully evicts the residual monomers from the LC volume and significantly improves electro-optical properties of the polymer-wall LC devices. The influence of the annealing process on the purity of LC-rich domain and the electro-optic properties of a LC cell was explored with a series of experiments. According to the experimental results, the annealing technique is extremely prospective for constructing flexible polymer-wall LC display applications. [ABSTRACT FROM AUTHOR]

The nematic liquid crystal alignment capability and electro-optical (EO) performance characteristics of in-plane switching (IPS) cells were first demonstrated on organic hybrid overcoat layers via ion beam irradiation. Usually the organic hybrid overcoat is used as the material for making a plate alignment layer in a colour filter process. To characterise the organic hybrid overcoat layer, we analysed the surface composition of the organic hybrid overcoat by X-ray photoelectron spectroscopy. The results show that the intensity of C = O and C-O bonding undergoes a change corresponding to the changes in energy of the ion beam exposure. Moreover, EO performance characteristics of IPS cells on the organic hybrid overcoat layer via ion beam irradiation were observed to have similar characteristics to the polyimide. [ABSTRACT FROM AUTHOR]

The compounds of poly (p-phenylene) are important materials for electro-optical and electronic applications. Algorithms for the calculation of the distances and hence the Wiener indices (W) of linear poly (p-phenylene) and cylindrical poly (p-phenylene) systems have been developed that require only the number of hexagonal rings present in the systems. Ambient conditions density and the bulk modulus of linear poly (p-phenylenes) with two to six phenyl rings have correlated with W1/4. Cylindrical poly (p-phenylene) systems with 5 and 6 phenyl rings are found to occur as intervening strands in between two caps of fullerene cages. [ABSTRACT FROM AUTHOR]

Optical limiting of the nanoobjects doped organic electrooptical materials have been studied in the visible and near infrared spectral range. It has been shown that the organic materials with nanoobjects can be used as nonlinear absorbers to protect human eyes and technical devices from high laser irradiation. The systems have been treated at the wavelength of 532, 633, 805, 1047, 1064, 1080, 1315, and 2940 nm. As an additional, the switching parameters of nanoobjects-doped liquid crystal compounds and improvement in the laser strength of the materials used as substrates for limiters and switchers have been shown. [ABSTRACT FROM AUTHOR]

We prepared a homologous series of non-symmetric dimesogenic compounds 1-(4- fluorophenyl)-4-{ω -{4-[4-(4-hexylphenyl)-2,3-difluorophenyl]phenyloxy}alkyloxy} benzene (I-n) and investigated the physical properties. For comparison, we also prepared a compound (II-6) possessing a 4-(4-cyanophenyl)benzene unit instead of the 4-(4- fluorophenyl)benzene unit. All the compounds exhibited an enantiotropic nematic phase. When an electric AC field was applied, a striped pattern that was similar to Williams domain appeared in the nematic phases of compounds I-n, whereas such a pattern was not observed in the nematic phase of II-6. We discuss structure-property correlations of the polar liquid crystal oligomers. [ABSTRACT FROM AUTHOR]

Polymer-stabilized ferroelectric liquid crystals (PSFLCs), in which a photocurable mesogenic monomer is doped into a ferroelectric liquid crystal and a UV photocure is carried out in the SmC* phase under the application of a bipolar AC electric field, show the monostable V-shaped electrooptical characteristics. In this research, we investigate the dependence of the molecular reorientational motion on the photocuring condition such as the tilt angle which FLC molecules take in the photocure stage and the frequency of the bipolar AC electric field, in terms of the response time measured from the electrooptical characteristics. [ABSTRACT FROM AUTHOR]

Chiral nematic liquid crystal (N*-LC)/aerosil particle (AP) composites were prepared. After the composite was sandwiched between ITO glass substrates, the inner surfaces of which had been treated for homogeneous orientation of LC molecules, the LC molecules tended to be aligned with planar texture. Upon the application of an electric filed, a focal conic texture with memory effect was induced and the composite exhibited light scattering. An electric field-induced homeotropic state was obtained after the application of a high electric field. The effects of the content of the APs and the pitch length of the N*-LC on the transmittances of the initial state and the focal conic texture, the driven voltage and the memory effect were investigated. [ABSTRACT FROM AUTHOR]

Two alkyl (1b and 1c) and four fluoroalkyl derivatives (1d-1f) of 4-arylbutyric acid (1c, 1d and 1e) and 4-arylbutanol (1b, 1f and 1g) [aryl = 2',3'-difluoro-4'-(2-(E-4-pentylcyclohexyl)ethyl)-biphenyl-1-yl] were prepared and investigated in the pure form as nematic materials (1b and 1c) and as additives to a ferroelectric liquid crystal (FLC) host (1d-1f). A comparison of 1b and 1c with the decyl analogue 1a demonstrates the effect of terminal chain modification on thermal and electro-optical properties. The substitution of the -CH2O- (1b) or -COO- (1c) for -CH2CH2- in 1a destabilized the N and SmA phases or completely eliminated the smectic behaviour (1c). Dielectric analysis revealed that the chain modification increased the negative Δε, reduced elastic constant K 11 and moderately decreased rotational viscosity γ1. The temperature dependence of the key electro-optical parameters was analysed for ester 2, the methyl analogue of 1c, which exhibits a 45 K wide N phase. All four fluoroalkyl derivatives 1d-1f showed enantiotropic SmA phases and 1e also exhibited a monotropic SmC phase. Solutions of 1d-1f in a FLC host (0.2 mmol g-1) increased the tilt angle Θ (up to 45° for 1g), reduced rotational viscosity γ1 and the risetime τ. The most dramatic changes were observed for 1g, which contains 15 fluorine atoms. [ABSTRACT FROM AUTHOR]

Polymer-dispersed liquid crystal (PDLC) films operating in reverse mode are transparent electro-optical devices, which can be turned into an opaque state by application of a suitable electric field. The effect was investigated of different UV powers, used during the polymerization process, on the electro-optical and morphology properties of PDLCs, working in reverse mode operation. Films were obtained by UV polymerization of mixtures of a low molecular weight nematic liquid crystal and a photopolymerizable liquid crystal monomer, homeotropically aligned by rough conductive surfaces. The electro-optical and morphology properties of samples were related to the polymerization conditions. Samples polymerized by lower UV powers exhibited "polymer ball" morphology and an electro-optical response due to the liquid crystal director reorientation, whereas samples obtained at higher UV powers showed a "Swiss cheese" morphology and an electro-optical response due to dynamic scattering. In addition, we observed by conductivity and IR measurements that UV exposure induces a degradation of the nematic liquid crystal. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop landslide susceptibility analysis techniques using artificial neural networks and then to apply these to the selected study areas of Gangneung in Korea. We aimed to verify the effect of data selection at training sites. Landslide locations were identified by the change detection technique of Korea Multipurpose Satellite (KOMPSAT-1) electro-optical camera (EOC) images, checked in the field, and a spatial database of topography, soil, forest, and land use was constructed. Sixteen landslide-related factors were extracted. These factors were used with an artificial neural network to analyse landslide susceptibility. Each factor weight was determined by the back-propagation training method. Five different data sets were applied to analyse and verify the effect of training. Landslide susceptibility indices were then calculated using the trained back-propagation weights, and susceptibility maps were constructed from Geographic Information System (GIS) data for five cases of difference training. The landslide susceptibility map was then compared with known landslide locations and verified. The result showed a prediction accuracy varying from 82.72% to 86.10%. The landslide susceptibility map can be used for land use planning to reduce hazards associated with landslides. [ABSTRACT FROM AUTHOR]

On the plane of sulfide bond lengths the ellipses of acentricity have been displayed for noncentrosymmetric (NCS) sulfide crystals distributed over 4 groups of polar and nonpolar paraferroelastics - ferroelastics. The dependence of nonlinear optical susceptibility χ(2) on the shortest sulfide bond length has been determined. Three characteristic regions are found inside the ellipses showing three different χ(2) levels: 1) crossing part of ellipses; 2) two symmetrical parts of ellipses outside crossing part. On this basis a method has been proposed for designing new acentric crystals promising a high χ(2) value. [ABSTRACT FROM AUTHOR]

On the plane of oxide bond lengths the ellipses of acentricity have been displayed for noncentrosymmetric (NCS) oxide crystals distributed over 4 groups of polar and nonpolar paraelastics - ferroelastics. The dependence of nonlinear optical susceptibility χ (2) on the shortest oxide bond length has been revealed. Three characteristic regions are found inside the ellipses showing three different χ(2) levels: (1) crossing part of ellipses; (2) two symmetrical parts of ellipses outside crossing part. On this basis a method has been proposed for design of new acentric crystals promising a high χ (2). [ABSTRACT FROM AUTHOR]

The present contribution reviews some aspect of the exploitation of polymeric and hybrid solgel materials for optoelectronic devices. In particular a procedure addressed to experimentally investigate the order stability of systems containing NLO dipolar molecules will be discussed. A figure of merit, allowing the comparison among candidate systems for devices, is recognized in the RT d33 decay time value. Its relation with glass transition temperature of a series of similar polymeric systems is reported. Moreover, a hybrid solgel system containing electro-optic active molecules is shown. [ABSTRACT FROM AUTHOR]

Switchable nematic emulsions are micron-sized droplets of nematic liquid crystal, floating in isotropic fluid matrices. Such droplets can be switched from an opaque (off) to a transparent (on) state by application of very low electric fields. It is known that the electro-optical properties of liquid crystal dispersions are affected by several parameters, including the liquid crystal loading. The electro-optical response of nematic emulsions has been investigated as a function of liquid crystal weight percentage. Almost transparent films with a reduced contrast ratio are obtained with lower liquid crystal contents. A macroscopic phase separation is observed when liquid crystal content exceeds 45 wt %. On the contrary, large contrast ratios and very low switching fields can be obtained if liquid crystal ranges from 25 to 35 wt %. Consequently, nematic emulsions prepared in this liquid crystal range can be used as promising systems for electro-optical applications. In addition to technological developments, these results can help computational and basic studies of phase separation in novel multiphase liquid crystalline materials. [ABSTRACT FROM AUTHOR]

We try to adopt a phase separated composite organic film (PSCOF) to a ferroelectric liquid crystal (FLC) cell. It has been found that in order to realize the PSCOF structure, it is important to select an adequate photocure condition such as the concentration of pre-polymer in LC medium, temperature and the UV intensity. The conventional FLC cell shows the so-called bistable hysteresis loop of electrooptical effect, whereas the PSCOF-FLC cell possesses a monostability without threshold. This monostablity is able to realize LC displays which possess grayscale capability. [ABSTRACT FROM AUTHOR]

We synthesized photoalignment material of high thermal resistance with hydroxyl aromatic polyimide, and studied the liquid crystal (LC) aligning capabilities on the photopolymer layers. Also, electro-optical (EO) performances for the twisted-nematic (TN)-liquid crystal display (LCD) photoaligned with linearly polarized UV exposure were investigated. A good LC alignment with UV exposure on the photopolymer surface can be obtained. However, the low pretilt angles were obtained below 1°. The voltage-transmittance curve without backflow bounce in the photoaligned TN cell with UV exposure was observed. The response time of photoaligned TN cell was measured about 24 ms. The residual DC voltage of photoaligned TN cell will be discussed. [ABSTRACT FROM AUTHOR]

We report studies on the influence of the alignment layers and the ionic impurities on the electro-optical behaviours of the twisted SmC* cells. A general expression of the internal electric field in the cell is given. Numerical results show clearly that the widening of the electro-optical response is connected to the alignment layers thicknesses. Dynamical studies of the ionic charges show that contrary to the classical SSFLC cells, ionic charges repartition is initially inhomogeneous in twisted SmC* cells. The azimuthal angle distribution and the transmitted light intensity are strongly affected by the ionic charges distribution. This model explain well the experimental behaviours of twisted SmC* cells. [ABSTRACT FROM AUTHOR]

In this paper two practical technological approaches are presented to demonstrate that liquid crystals can be employed to make low cost integrated optic devices with characteristics required for optical communication systems. In a first approach ferroelectric and nematic liquid crystals are combined with ion-exchanged glass waveguides to produce high performing optical switches. A polarization independent configuration of such switches is also shown. In a second approach nematic liquid crystals are embedded in SiO2/Si V-grooves to produce channel waveguides. Modal and polarization properties of such novel liquid crystal waveguides are experimentally demonstrated. [ABSTRACT FROM AUTHOR]

Horizontally surface-stabilized orthoconic antiferroelectric liquid crystals (OAFLCs) provide excellent contrast electrooptic switching. However, in very thin cells the bulk relaxation to the anticlinic state tends to be slow because the synclinic state is upheld by the surfaces. In cells thin enough to accomplish a surface-stabilized state of today's short-pitch OAFLC mixtures, the field-induced synclinic (ferroelectric) states often become metastable making the corresponding bright electrooptic state prevail for long times after the electric field is switched off. Fast relaxation is then achieved by specially designed waveforms.By introducing a polymer network formed by in-situ photopolymerization of a small concentration of a commercial reactive monomer dissolved in the OAFLC, we have succeded to drastically reduce the time for relaxation from the synclinic to the anticlinic state after switching off the field down to about 3 milliseconds at room temperature, without the use of any tailored electronic waveforms. The relaxation time of the polymer stabilized OAFLCs (PS-OAFLCs) is thus shorter than in todays nematic liquid crystal displays, which make PS-OAFLCs attractive for use in future high-contrast, blur-free displays. [ABSTRACT FROM AUTHOR]