Showing papers in "Liquid Crystals in 2013"
TL;DR: The first successful commercialization of triphenylene-based discotic liquid crystals (DLCs) has been accomplished in the Fuji WideView optical compensation films as mentioned in this paper, and more than 1000 DLC derivatives have been synthesized and investigated starting from structure-properties to structure-device performance.
Abstract: Since the early work of Chandrasekhar and his co-workers on hexaesters of benzene published in 1977, discotic liquid crystals (DLCs), in particular, triphenylene-based DLC materials have been investigated intensively, especially over the last decade. The first successful commercialisation of triphenylene-based DLCs has been accomplished in Fuji ‘Wide-View’ optical compensation films. DLCs represent a broad well understood class of soft matter which possess the ability to self-organise into highly anisotropic and ordered structures such as columns that function not only as organic anisotropic semiconductors, but also contribute to the development of new smart materials in the field of organic electronics for many device applications such as photovoltaic devices, light-emitting diodes, field-effect transistors, memory elements, and sensors. Over the last 35 years, more than 1000 triphenylene derivatives have been synthesised and investigated starting from structure-properties to structure-device performance...
122 citations
TL;DR: In this paper, the effects of doping of NPs on dielectric and electro-optic properties of LC-NP composites have been discussed in reference of Maier and Meier theory.
Abstract: Thermodynamical, optical, dielectric and electro-optical characterisation of nematic liquid crystals (LCs) and silver nanoparticle (NP) composites have been carried out. Transition temperatures of pure and composites systems have been measured. Thermodynamical studies suggest increase of clearing temperature of the composite material as compared to the pure material. Threshold voltage for switching from bright to dark state and splay elastic constant of the pure and composite materials have been determined. From frequency dependence of dielectric measurements, permittivity, loss, relaxation frequency and dielectric strength of flip-flop mechanism of LC molecules in the nematic phase have been calculated. Dielectric properties of composites have been explained in reference of Maier and Meier theory. The effects of doping of NPs on dielectric and electro-optic properties of LC-NP composites have been discussed.
81 citations
TL;DR: In this paper, the authors measured the splay and bend elastic constants in the ordinary nematic phase of a dimer material, CBC11CB, for temperatures down to 0.6°C above the Nx-Nu transition.
Abstract: The second nematic phase found in some bimesogenic liquid crystals with an odd flexible spacer has aroused considerable interest due to many unusual properties exhibited by them. However, the reason for such molecules to exhibit transitions to the modulated phase is still unclear. Dozov [Europhys Lett. 2001;56:247] predicted that negative K 33 can lead to a modulated phase where the director has either splay-bend or twist-bend distribution. Though various theoretical studies have suggested that this scenario may be valid, no experimental evidence has so far been given. In order to study the influence of the elastic constants, we measured the splay and bend elastic constants in the ordinary nematic phase of a dimer material, CBC11CB, for temperatures down to 0.6°C above the Nx–Nu transition. Our results show that the bend constant is reduced by a factor of 2 compared with that closer to the I-Nu transition but is positive and the trend does not seem that K 33 will extrapolate to zero or fall below it for t...
66 citations
TL;DR: In this paper, a post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale.
Abstract: A post-synthesis alignment of individual single-walled carbon nanotubes (SWCNTs) is desirable for translating their unique anisotropic properties to a macroscopic scale. Here, we demonstrate excellent dispersion, orientation and concomitant-polarised photoluminescence of SWCNTs in a nematic chromonic liquid crystal. The methods to obtain stable suspension are described, and order parameters of the liquid crystal matrix and of the nanotubes are measured independently.
55 citations
TL;DR: In this article, the mesophase behavior was investigated by polarising optical microscopy and differential scanning calorimetry, and a representative example has also been characterised by X-ray diffraction (XRD) studies.
Abstract: Three new series of bent-shaped molecules with 4-chlororesorcinol, 4-bromoresorcinol or 4-fluororesorcinol as the central unit, and azobenzene with different alkoxy chain length as side arms were synthesised. The mesophase behaviour was investigated by polarising optical microscopy, and differential scanning calorimetry. A representative example has also been characterised by X-ray diffraction (XRD) studies. It is found that almost all of the materials prepared are monotropic liquid crystalline. Depending on the substituent at the central unit and on the chain length nematic phases, B6 phases, a B4-like dark conglomerate phase and a modulated/undulated anticlinic SmC phase were found. As a unique feature, upon reducing the chain length a transition from nematic to B6-type smectic phases was observed, which is reverse to usually observed phase sequences. The UV–vis absorption spectroscopy was also performed to study the effect of light-induced trans–cis-isomerisation on the prepared compounds.
54 citations
TL;DR: In this paper, the synthesis of new laterally alkyl substituted high birefringent quaterphenyl and phenylethynyltolane liquid crystals with isothiocyanate terminal group was reported.
Abstract: We report the synthesis of new laterally alkyl substituted high birefringent quaterphenyl and phenylethynyltolane liquid crystals with isothiocyanate terminal group. The thermal and optical properties such as birefringence are measured and discussed based on their molecular structures. The compounds exhibit birefringence (Δn) in the range of 0.44–0.63, and are expected to be appropriate components of high birefringent nematic mixtures for various applications.
46 citations
TL;DR: In this article, a set of chiral unsymmetrical dimeric liquid crystals consisting of a cholesterol moiety as chiral entity and a substituted salicylidene imine core interconnected through an even methylene spacer have been synthesized and their mesomorphic properties are characterised.
Abstract: Chiral unsymmetrical dimeric liquid crystals consisting of a cholesterol moiety as chiral entity and a substituted salicylidene imine core (with the substituent being butyl or fluoro or chloro group) interconnected through an even methylene spacer have been synthesised and their mesomorphic properties are characterised. All the dimers exhibit enantiotropic mesophases. The butyl homologue exhibited N* phase only, the fluoro- and chloro-substituted compound exhibited frustrated blue phases (BPs), N* phase and SmC* or twisted grain boundary (TGB) phases. The occurrence of a fluid frustrated phase, the BP, in particular, observed in compounds with a polar moiety and bent optimised conformation by density functional theory (DFT) study, indicates the importance of polar structures and bent shape of the compounds. Theoretical calculation was performed in order to study the optimised conformation, polarity and electron density distribution of the synthesised cholesterol derivatives using DFT. Time-dependent densi...
45 citations
TL;DR: In this article, the authors focus on the so-called orthoconic antiferroelectric LCs (OAFLCs), which can provide the fast switching of conventional antiferrogenic LCs, but combined with a potentially much higher optical contrast.
Abstract: The ubiquitous liquid crystal display (LCD) is based on nematic liquid crystals (LCs) and has during 40 years developed from simple few digit displays into high-resolution flat-panel displays. A last and very important step towards the present TVs was the combination with thin film transistors that also led to the introduction of several new switching modes. Despite the enormous success of this technology, there is presently a renewed interest in LCs with faster electrooptic response, especially for future 3D vision display systems and possibly for field-sequential-colour (FSC) generation displays. Here, I focus on the so-called orthoconic antiferroelectric LCs (OAFLCs), which can provide the fast switching of conventional antiferroelectric LCs, but combined with a potentially much higher optical contrast. The reason is that the dark state of orthconic materials has a homeotropic optic axis, which makes the extinction ideally complete between crossed polarisers and independent of in-plane alignment fluctuations characteristic of all antiferroelectric LCs. The basic features and device physics issues of orthoconic LCs are reviewed and the most important remaining challenges to be met in terms of materials development are discussed in this article. Furthermore, a few examples of new applications made possible with the use of present and future orthoconic materials are given. © 2013 Copyright Taylor and Francis Group, LLC.
44 citations
TL;DR: In this paper, four series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different lateral substituents and terminal alkoxy chain length were synthesized and characterised.
Abstract: Four series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different lateral substituents and terminal alkoxy chain length were synthesised and characterised. Then, all these bent-shaped compounds were separately doped into the blue phase (BP) liquid crystal host and their effects on the BP range of the host were investigated, which shows that the BP ranges varied greatly with the difference in the structure of 2,5-disubstituted 1,3,4-oxadiazoles and their doped concentration. Moreover, in order to explore the influence of the inherent molecular geometry and properties of the bent-shaped molecules on the stability of BPs, the molecular structures of all the compounds were studied by using the theory of density functional theory, and the optimised structural parameters of the molecules were calculated at the B3LYP/6–31G* level.
41 citations
TL;DR: Aryl-substituted β-diketonate adducts with 5,5′-di(heptadecyl)-2,2′-bipyridine has been synthesized.
Abstract: A series of aryl-substituted β-diketonate adducts with 5,5′-di(heptadecyl)-2,2′-bipyridine has been synthesised. All the compounds exhibit a mesomorphic (smectic) behaviour. It has been shown that the metal ion does not drastically influence the mesophase type and the transition temperatures. A thin film of Eu(III) complex shows more effective luminescence in the aligned state.
37 citations
TL;DR: In this article, microbullets with homeotropic surface anchoring are dispersed in 4-cyano-4′-pentylbiphenyl nematic liquid crystal (NLC) cells and form oriented elastic dipoles with a nematic point defect located near the curved end.
Abstract: Microbullet particles, cylinders with one blunt end and one hemispherical end, offer a novel platform to study the effects of anisotropy and curvature on colloidal assembly in complex fluids. Here, we disperse microbullets in 4-cyano-4′-pentylbiphenyl nematic liquid crystal (NLC) cells and form oriented elastic dipoles with a nematic point defect located near the curved end. This feature allows us to study particle interactions as a function of dipole alignment. By careful control of the surface anchoring at the particle surface and the confining boundaries, we study the interactions and assembly of microbullets under various conditions. When microbullets with homeotropic surface anchoring are dispersed in a planar cell, parallel dipoles form linear chains parallel to the director, similar to those observed with spherical particles in a planar cell, while antiparallel dipoles orient side-to-side. In a homeotropic cell, however, particles rotate to orient their long axis parallel to the director. When so a...
TL;DR: In this paper, the effect of Cadmium selenide quantum dot (CdSe QD) on different electro-optical (E-O) properties has been studied in the SmC* phase.
Abstract: Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system.
TL;DR: In this paper, a truxene discogen was synthesized with improved yields, and the mesomorphism has been investigated by using polarised optical microscopy, differential scanning calorimetry and X-ray diffraction.
Abstract: Discotic liquid crystals as a kind of promising organic electronic materials show self-assembly property as well as high charged carrier mobility. New truxene discogens, six 3,8,13-tri(alkoxy)-2,7,12-tri(methoxy)truxenes and two 3,8,13-tri(alkoxy)-2,7,12-tri(hydroxy)truxenes, have been synthesised with improved yields, were fully characterised and exhibited good thermal stability. The mesomorphism has been investigated by using polarised optical microscopy, differential scanning calorimetry and X-ray diffraction, and they exhibited ordered hexagonal columnar mesophase. More importantly, the charge carrier mobilities of 6d and 7f have been measured by using time-of-flight technique and 7f displayed hole drift mobility rate of 4.2 × 10−2 cm2 V−1 s−1 in the Colho phase and 0.1 cm2 V−1 s−1 at a lower temperature M mesophase.
TL;DR: In this paper, the synthesis and characterisation of a new type of benzoxazole-terminated heterocyclic compounds, 2-(4ʹ-alkoxybiphenyl-4-yl)-benzoxazoles derivatives (nB-x), are reported.
Abstract: The synthesis and characterisation, and mesomorphic and photophysical properties of a new type of benzoxazole-terminated heterocyclic compounds, 2-(4ʹ-alkoxybiphenyl-4-yl)-benzoxazole derivatives (nB-x), are reported. For better understanding of the structure–property relationships, compounds bearing a variety of polar substituents in the 5-position of the benzoxazole moiety were prepared, including H (nB-H), NO2 (nB-N), CH3 (nB-M) and Cl (nB-C). Their phase transition behaviour was investigated by differential scanning calorimetry and polarising optical microscopy. In the case of carbon atoms in the alkoxy chain between 2 and 10 they exhibited enantiotropic smectic mesophases, for which the mesophase ranges were 101–175°C and 159–182°C on heating and cooling for nB-N, 5–63°C and 19–63°C for nB-H, 81–90°C and 78–96°C for nB-M, and 131–132°C and 131–132°C for nB-C, respectively. The effect of the length of the alkoxy chain on mesomorphic properties was studied. Compounds nB-N, nB-M and nB-C exhibited a muc...
TL;DR: In this article, the authors review both commonly used, and more recently developed visual presentation methods that expose different aspects of the textures, from the topological content of nematic defects, to deformation modes and simulated optical effects.
Abstract: In analysis of numerically simulated or experimentally obtained nematic textures, data visualisation plays an important role in interpretation and comparison of results. We review both commonly used, and more recently developed visual presentation methods that expose different aspects of the textures, from director field patterns and topological content of nematic defects, to deformation modes and simulated optical effects. We outline the theoretical background and potential uses, with examples that highlight the features of each of the described techniques.
TL;DR: In this article, a new synthetic approach for the chiral terphenyl- and quaterphenylbased diesters, bis[(1S)-1-methylheptyl] 1,1′:4′,1″-terphenyl 4,4″-dicarboxylates and bis[1S]-1-methyltetrameric 1.1
Abstract: A new synthetic approach for the chiral terphenyl- and quaterphenyl-based diesters, bis[(1S)-1-methylheptyl] 1,1′:4′,1″-terphenyl-4,4″-dicarboxylates and bis[(1S)-1-methylheptyl] 1,1′:4′,1″:4″,1″′-quaterphenyl-4,4″′-dicarboxylates, has been developed and optimised. The approach presented allows the synthesis of a range of laterally substituted oligophenyl diesters in good yield. A number of pairs of S,S and R,R isomers have been synthesised and their thermodynamic properties measured. Most of the compounds have very good solubility in a variety of liquid crystalline host mixtures, and moderate helical twisting power, which has been determined for a number of nematic materials, either dielectrically positive or negative. The high birefringence of the oligophenyl core makes them suitable candidates as chiral dopants for medium to highly birefringent nematic materials for generating cholesteric and blue phase materials.
TL;DR: In this paper, the attributes of the cluster biaxial nematic exhibited by bent-core mesogens derived from the oxadiazole biphenol mesogenic core are reviewed.
Abstract: Herein we review the attributes of the cluster biaxial nematic exhibited by bent-core mesogens derived from the oxadiazole biphenol mesogenic core. We present an array of static 2H NMR spectra as well as 2D powder spectra generated by rotating the nematic phase of directly labelled mesogens. Analysis of these motionally averaged NMR observations requires the nematic phase to have monoclinic symmetry. X-ray diffraction data, in particular the effects of electric and magnetic field effects, are also consonant with the cluster picture of this biaxial nematic phase.
TL;DR: In this paper, a method for vertical alignment (VA) of liquid crystals (LCs) without alignment layers was proposed by mixing only a very low concentration (0.05 wt%) of an organic compound with LCs.
Abstract: We propose a method for vertical alignment (VA) of liquid crystals (LCs) without alignment layers by mixing only a very low concentration (0.05 wt%) of an organic compound with LCs. The electro-optic characteristics of a VA cell fabricated by the proposed method were almost the same as those of a conventional VA cell with VA layers. Moreover, we used the proposed method to realise a polymer-stabilised VA device with a rapid response time without alignment layers. The proposed method can simplify the fabrication process and reduce the manufacturing cost of LC display devices by removing the need for alignment layers and the alignment process such as coating of polyimide layers and the UV exposure for the photo-alignment. We believe that the proposed method can play an essential role in the fabrication of plastic flexible LC display devices requiring the low-temperature process.
TL;DR: In this paper, a series of linear molecules of 4-(n-(2,3,5,6-tetrafluoro-4-iodophenoxy)alkoxy)benzoic acid (4a-d) bearing a hydrogen-bond donor on one end of the molecule and a halogen-bund donor on another end was synthesized.
Abstract: A series of linear molecules of 4-(n-(2,3,5,6-tetrafluoro-4-iodophenoxy)alkoxy)benzoic acid (4a–d) bearing a hydrogen-bond donor on one end of the molecule and a halogen-bond donor on another end was synthesised. Compounds 4a–d formed composite halogen- and hydrogen-bonded polymeric complexes with bis(4-trans-4′-stilbazolyl)-oligo(ethylene glycol) (5a-c), as verified by Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). The degree of polymerisation of complexes 4a–d/5a–c was estimated to be in the range of 11–25 using the Flory equation, suggesting the polymeric nature of the complexes. The complexes 4a–d/5a–c showed thermotropic mesophases upon cooling, confirmed by polarised optical microscopy and DSC. The liquid crystals exhibited significantly broader mesophase temperature ranges than those induced by the halogen bond alone, indicating that the introduction of a more flexible hydrogen-bonded mesogenic core in halogen-bonded polymeric assembly likely led to a marked im...
TL;DR: In this paper, features of glass transition in liquid crystalline nematic and smectic E, B and IA phases of selected materials observed by means of the polarising microscopy and Fourier transform infrared spectroscopy (FTIR) are reported.
Abstract: Features of glass transition in liquid crystalline nematic and smectic E, B and IA phases of selected materials observed by means of the polarising microscopy and Fourier transform infrared spectroscopy (FTIR) are reported. Evolution of cracking in the glass and a coincidence of its disappearance temperature with the glass transition temperature (Tg) on heating is shown and discussed in the context of processes that occur in the glass. The shape of temperature dependencies of absorption bands is shown as the signature of the glass transition.
TL;DR: In this article, a newly synthesized ferroelectric liquid crystal (FLC) material, namely LAHS 22, has been characterised using dielectric relaxation spectroscopy, differential scanning calorimetry and polarisation optical microscopy.
Abstract: In this article, a newly synthesised ferroelectric liquid crystal (FLC) material, namely LAHS 22, has been characterised. The characterisation of the FLC material has been performed using dielectric relaxation spectroscopy, differential scanning calorimetry and polarisation optical microscopy. We observed an enhancement in the dielectric and electro-optical properties of the FLC material by incorporating gold nanoparticles (GNPs)-decorated multiwalled carbon nanotubes (MWCNTs). The GNPs-decorated MWCNTs cause an increment in dielectric dispersion (up to kHz), absorption, spontaneous polarisation and rotational viscosity of the FLC material. The pure and GNPs-decorated MWCNTs doped FLC cells were analysed by means of various dielectric spectroscopic and optical measurements. The observed enhancement in the dielectric and electro-optical properties of the FLC material has also been studied with concentration of GNPs-decorated MWCNTs in FLC material. The GNPs-decorated MWCNTs/FLC composites are not only of f...
TL;DR: In this paper, the electro-optical properties of the homogeneous aligned nematic liquid crystal (N-LC) doped with cobalt oxide (Co3O4) nanoparticles (NPs) were investigated.
Abstract: In this article, we study the electro-optical (EO) properties of the homogeneous aligned nematic liquid crystal (N-LC) doped with cobalt oxide (Co3O4) nanoparticles (NPs). The EO characteristics of Co3O4 doped N-LC are higher performance, indicating lower threshold voltage (1.33 V), faster rising time (1.479 ms), and faster falling time (9.343 ms) than pure liquid crystal (LC) cells. We have demonstrated these results by investigating the relationship between dielectric constants and LC device properties. Furthermore, we proved NPs doped N-LC cells drive low power operation without capacitance hysteresis. Our experimental results were verified by software simulation based on general physical properties.
TL;DR: In this article, a series of 10 new symmetric compounds containing three hexyl-bridged imidazolium bromide units as the core and two terminal n-alkyl chains was synthesized and analyzed.
Abstract: Imidazolium-containing thermotropic ionic liquid crystals (TILCs) are of interest because of their structural similarity to imidazolium-based ionic liquids (ILs), allowing them to exhibit some IL-like properties in addition to the LC order. More imidazolium units are important for increasing the IL character; however, the effect of multiple imidazolium units on LC behaviour is not well known. Most reported imidazolium TILCs contain one imidazolium unit; only a handful containing multiple imidazolium units is known. The only examples of TILCs with multiple imidazolium units sequentially linked with a flexible spacer are based on an alkyl- or oligo(ethylene oxide)-bridged bis(imidazolium) core with an n-alkyl tail at each end. Herein, a series of 10 new symmetric compounds containing three hexyl-bridged imidazolium bromide units as the core and two terminal n-alkyl chains was synthesised and analysed. Thermotropic LC phases were generally not observed for homologues with even-numbered tails less than 16 car...
TL;DR: In this article, the synthesis of 4-butyl-4′-[(4butyl]-2,6-difluorophenyl)ethynyl]biphenyl and its higher fluorinated analogues is presented and discussed.
Abstract: The synthesis of 4-butyl-4′-[(4-butyl-2,6-difluorophenyl)ethynyl]biphenyl and its higher fluorinated analogues is presented and discussed. Correlations between molecular structure and mesomorphic properties for presented compounds as well as other known from the literature analogues have been drawn. The dielectric study of four synthesised compounds and their mixtures are presented and discussed. Trifluoro-substituted analogues are trade off between low dielectric anisotropy of difluorinated compounds and lower clearing points of tetrafluorinated ones.
TL;DR: Examples of biologically inspired systems, which form LC phases with their LC nature impacting biological function in cells or being important in biomedical applications are presented.
Abstract: In this paper, which is part of a collection in honour of Noel Clark’s remarkable career on liquid crystal (LC) and soft matter research, we present examples of biologically inspired systems, which form LC phases with their LC nature impacting biological function in cells or being important in biomedical applications. One area focuses on understanding network and bundle formation of cytoskeletal polyampholytes (filamentous actin, microtubules and neurofilaments (NFs)). Here, we describe studies on NFs, the intermediate filaments of neurons, which form open network nematic LC hydrogels in axons. Synchrotron small-angle-X-ray scattering studies of NF protein dilution experiments and NF hydrogels subjected to osmotic stress show that NF networks are stabilised by competing long-range repulsion and attractions mediated by the NF’s polyampholytic sidearms. The attractions are present both at very large inter-filament spacings, in the weak sidearm-interpenetrating regime, and at smaller inter-filament spacings,...
TL;DR: The mesomorphic, thermoptic and glass-forming properties of 4-[6-((cholesteryloxy) carbonyl)oxy hexyloxy] benzoic acid (Ch-BA) have been investigated as a novel supramolecular hydrogen-bonded cholesteric mesogen as mentioned in this paper.
Abstract: The mesomorphic, thermoptic and glass-forming properties of 4-[6-((cholesteryloxy) carbonyl)oxy hexyloxy] benzoic acid (Ch-BA) have been investigated as a novel supramolecular hydrogen-bonded cholesteric mesogen. Fourier transform infrared and 1H nuclear magnetic resonance studies have confirmed the chemical structure and the hydrogen-bond formation between the mesogens. According to polarising optical microscope observations, the compound exhibited smectic and chiral nematic phases. Differential scanning calorimetry indicated an unexpected glass transition (T g) around 32°C and a liquid crystalline region between 32 and 122°C, in which the cholesteric phase appeared at 80°C. As a result of the glass formation, samples of Ch-BA which were rapidly cooled below the T g were found to preserve the long-range ordering of the liquid crystalline state and retained the iridescent colours of the cholesteric phase. These results led to the conclusion that the formation of identical dimers by intermolecular hydrogen...
TL;DR: In this paper, a bistable smectic A (SmA) liquid crystal (LC) device based on polymer-dispersed liquid crystal mode was demonstrated, in which SmA PDLC films were prepared from ultraviolet (UV) irradiation-induced polymerisation of the acrylate monomers in acrylated monomers/ion-doped SmA LCs mixtures.
Abstract: In this study, a bistable smectic A (SmA) liquid crystal (LC) device based on polymer-dispersed liquid crystal (PDLC) mode was demonstrated, in which SmA PDLC films were prepared from ultraviolet (UV) irradiation-induced polymerisation of the acrylate monomers in acrylate monomers/ion-doped SmA LCs mixtures. The effects of the constitute of the mixtures, functionality (crosslinker concentration), polymerisation temperature and the UV light intensity on the microstructure of the polymer network and electro-optical performance in bistable SmA PDLC films were investigated in detail. The moderate size of SmA LC microdrop and dispersibility of polymer matrix in LCs played important role in determining the performances of PDLC. Photopolymerisation temperature and UV light intensity were able to improve the morphology of polymer matrix and electro-optical performance of PDLC device. This device enables the possibility of industrial production such as smart electronic control glass, which can be fabricated by the...
TL;DR: In this paper, a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers is presented.
Abstract: We present a detailed theoretical and experimental study of the reflectance response of a deformed-helix ferroelectric (DHF) liquid crystal (LC) cell to an applied voltage under cross-polarisers. Using a model based on the effective dielectric tensor approximation, we derive simple analytical formulas to design a LC cell with maximum modulation depth and optimal linearity of the electro-optical response intensity versus the electric field. Our experimental results show that the cell works at frequencies up to 10 kHz and exhibits excellent linearity, with a total harmonic distortion as low as −70 dB. These findings suggest that DHF-LCs can be exploited to develop simple and accurate optical sensors.
TL;DR: In this article, the authors describe classroom experiments on controlled generation of umbilics in a nematic layer with homeotropic anchoring conditions submitted to an electric field, and reveal the winding action of rotating localised magnetic fields and the winding reversal induced by Poiseuille flows.
Abstract: Umbilics in a nematic layer can be seen as topological defects of a complex order parameter. Being analogous to vortex lines in superfluids or superconductors, they are much easier to handle. We describe classroom experiments on controlled generation of umbilics in a nematic layer with homeotropic anchoring conditions submitted to an electric field. For this purpose we submit nematic samples to magnetic fields created by small NdFeB magnets. Umbilics induced by applied fields are unveiled by observation between crossed polarisers in monochromatic or white light. We report also on the winding action of rotating localised magnetic fields and on the winding reversal induced by Poiseuille flows.
TL;DR: Triple diamino-bridged cyclotriphosphazene (1) was reacted in a 1:8 stoichiometry with the sodium derivatives of long-chain diols [1-octanol, 1-decanol and 1-hexadecanol] tetrahydrofuran (THF) at room temperature to form hexa-substituted cyclotrizene derivatives (2, 3, 4 and 5, respectively), whose mesomorphic behaviours were investigated for their possible applications as liquid crystals as discussed by the authors.
Abstract: Triple diamino-bridged cyclotriphosphazene (1) was reacted in a 1:8 stoichiometry with the sodium derivatives of long-chain diols [1-octanol, 1-decanol, 1-dodecanol, 1-hexadecanol] tetrahydrofuran (THF) at room temperature to form hexa-substituted cyclotriphosphazene derivatives (2, 3, 4 and 5, respectively), whose mesomorphic behaviours were investigated for their possible applications as liquid crystals. The cylindrical-type cyclotriphosphazene derivatives (2–5) were characterised by mass and elemental analyses and by Fourier transform infrared spectroscopy (FT-IR), 1H and 31P {1H} NMR spectroscopies. The thermal and mesomorphic properties were investigated by differential scanning calorimetry and by polarising optical microscopy, respectively. It was found that liquid crystal materials could be obtained from compounds 3 and 4 with alkoxy chains rather than using aromatic ring(s) as mesogens as published previously.