Showing papers in "Liquid Crystals in 2015"
TL;DR: In this paper, the formation of liquid crystal and soft crystal phases as a consequence of minimizing the free volume of the system either through design engineering of molecular shape or molecular shape optimization.
Abstract: In this article, we probe the formation of liquid crystal and soft crystal phases as a consequence of minimising the free volume of the system either through design engineering of molecular shape o...
149 citations
TL;DR: In this article, six new non-symmetric dimers belonging to the family of compounds the (R,S)-(benzylidene-4-substituted-aniline)-2ʺ-methylbutyl-4ʹʹ-phenyloxy) benzoate-oxy) hexanoates have been prepared and their thermal behaviour characterised.
Abstract: Six new non-symmetric dimers belonging to the family of compounds the (R,S)-(benzylidene-4ʹ-substituted-aniline)-2ʺ-methylbutyl-4ʹʹʹ-(4ʹʹʹʹ-phenyloxy) benzoate-oxy) hexanoates have been prepared and their thermal behaviour characterised. The terminal substituents on the 4-benzylideneaniline fragment are H, CH3, C2H5, Cl, Br and I. All six dimers exhibit an enantiotropic nematic phase, and the efficiency of the terminal substituent in enhancing the nematic–isotropic transition temperature is largely consistent with that established for conventional low molar mass liquid crystals. This trend is discussed in terms of the size of the terminal substituent and its effect on the shape of the molecule. The halogen-substituted and ethyl-substituted dimers also exhibit smectic behaviour. For the halogen-substituted dimers, the driving force for smectic phase formation is considered to be, at least in part, the specific anisotropic interaction between the unlike mesogenic units. In contrast, for the ethyl-substitute...
102 citations
TL;DR: The phase behavior of equimolar mixtures of 6-(4-cyanobiphenyl-4-yl)hexyloxybenzoic acid (CB6OBA) is reported in this article.
Abstract: The phase behaviour of equimolar mixtures of 6-(4ʹ-cyanobiphenyl-4-yl)hexyloxybenzoic acid (CB6OBA) with either 1-(4-butylazobenzene-4ʹ-oxy)-5-(4-oxypyridine)pentane (BuABO5OPyr) or 1-(4-butylazobenzene-4ʹ-oxy)-6-(4-oxypyridine)hexane (BuABO6OPyr) is reported. CB6OBA shows a monotropic twist-bend nematic phase and an enantiotropic nematic phase whereas the two pyridyl-based components do not exhibit liquid crystallinity. Both equimolar mixtures (CB6OBA/BuABOnOPyr) show enantiotropic nematic phases. The nematic-isotropic transition temperature and associated entropy change are higher for the CB6OBA/BuABO6OPyr mixture than for the CB6OBA/BuABO5OPyr mixture. This may be accounted for in terms of the average shapes of the hydrogen-bonded 1:1 complexes formed between the two differing components in the mixtures. However, Fourier transform infrared spectroscopy reveals that this complex is not formed quantitatively, but instead a complex mixture exists over the complete temperature range studied, involving the ...
77 citations
TL;DR: In this paper, the formation of arrays of focal conic defects (FCDs) was studied in the twist-bend nematic, Ntb, phase, and some of the focal conics exhibit submicron internal structure with 8nm periodicity, which is very close to that found in the crystalline phase of the material.
Abstract: Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical textures related to the formation of arrays of focal conic defects (FCDs). Some of the focal conics exhibit submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, that might suggest surface freezing.
75 citations
TL;DR: The development and realisation of applications utilising the cholesteric or chiral nematic phase have benefited from the materials research work carried out by George Gray and his colleagues as mentioned in this paper.
Abstract: The development and realisation of applications utilising the cholesteric or chiral nematic phase have benefited from the materials research work carried out by George Gray and his colleagues. His work on cholesteric materials started in the 1950s with the synthesis of cholesteryl esters and the observation in them of an unusual blue fog phase which he later studied in more detail. He went on to identify the molecular features that give rise to the characteristic cholesteric helical structure and the role of molecular structure and chirality on the properties of the cholesteric phase. This pioneering work paved the way for a wide range of applications of which a few are exemplified.
69 citations
TL;DR: The liquid crystal dimer 1ʺ,7ʺ-bis (4-cyanobiphenyl-4ʹ-yl) heptane (CB7CB) has been shown to possess a nematic-nematic phase transition at 376 K as mentioned in this paper.
Abstract: The liquid crystal dimer 1ʺ,7ʺ-bis(4-cyanobiphenyl-4ʹ-yl) heptane (CB7CB) has been shown to possess a nematic–nematic phase transition at 376 K. The phase below this temperature has been identified...
61 citations
TL;DR: In this article, the ionic behavior in nanoparticles (NPs) dispersed nematic liquid crystal has been investigated and it is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension.
Abstract: The present study focuses on the ionic behaviour in nanoparticles (NPs) dispersed nematic liquid crystal. Dielectric spectroscopy has been used to investigate the behaviour of ions in suspension of NPs and liquid crystal (LC). Ionic concentration, diffusion coefficient, activation energy and mobility have been calculated from dielectric data. It is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension. The initial increase in ion concentration is attributed to the insertion of more ions due to impurities of TiO2 NPs and various other reasons. Temperature dependence of diffusion constant for different loading of TiO2 NPs is also investigated. The activation energy of NPs dispersed LC is found to be lower than the pristine one and it decreases with increasing concentration of NPs. The decreasing DC conductivity with increasing NPs concentration is attributed to the hindered or restricted motion of ions in the suspension. It is proposed that...
60 citations
TL;DR: In this article, a polymer-dispersed liquid crystal (PDLC) system based on polysulfone as carrying matrix and 4-cyano-4-pentylbiphenyl (5CB) liquid crystal was obtained as thin transparent films.
Abstract: Polymer-dispersed liquid crystal (PDLC) systems based on polysulfone as carrying matrix and 4-cyano-4ʹ-pentylbiphenyl (5CB) liquid crystal (LC) were obtained as thin transparent films The PDLC films were prepared by solvent- and thermally induced phase separation methods, with various compositions in the two components Information on the phase separation was obtained by polarised light optical microscopy, differential scanning calorimetry and scanning electron microscopy The PDLC composites show well-defined droplets of submicrometric size, around 650 nm for a medium content of LC and around 250 nm for a low one The droplets show a radial configuration and a homeotropic alignment of the LC molecules within By contact angle measurement and surface free energy calculations, it was established that self-assembling of aliphatic units of the two composite components, at droplet interface, is the driving force of the homeotropic alignment Moreover, these data indicated the potential biocompatibility of th
59 citations
TL;DR: In the early 1970s, the twisted-nematic liquid crystal display (TN-LCD) technology and subsequent polarisation-controlled field effect LCDs strongly depended on the discovery, development and manufacturing of novel nematic liquid crystals as discussed by the authors.
Abstract: Since 1970, scientific and technological progress of the twisted-nematic liquid crystal display (TN-LCD) technology and subsequent polarisation-controlled field-effect LCDs strongly depended on the discovery, development and manufacturing of novel nematic liquid crystals. New experimental techniques had to be developed for determining all display-relevant LC-material parameters and correlating them with molecular structural elements and display performance. TN-LCDs with low operating voltage and power consumption, faster response, broader operating temperature range, multiplexability and, last but not least, long lifetime were some of the goals. Progress in LC-material R&D, device physics and display manufacturing broadened the range of TN-LCD applications from seven-segment, directly addressed displays in the early 1970s to increasingly more complex LCDs with higher information content. Examples include super-twisted nematic-LCDs in the 1980s and thin-film transistor-addressed TN-LCD monitors in the 1990...
58 citations
TL;DR: In this article, the authors studied the properties of pure 8CB and its composites with gold and silver nanoparticles and found that Ionic conductivity increases significantly in nematic and smectic Ad (SmAd) phases, whereas dielectric anisotropy is almost unchanged for both the nanocomposites.
Abstract: Thermodynamical, dielectric, optical and electro-optical characterisation of pure 8CB and its composites with gold and silver nanoparticles have been studied. Thermodynamical studies suggest a decrease in clearing temperature of the nanocomposite systems as compared to the pure system. Dielectric parameters of pure nematic liquid crystal and nanocomposites in the homeotropic and planar aligned samples have been measured in the frequency range of 1–35 MHz. Ionic conductivity increases significantly in nematic and smectic Ad (SmAd) phases, whereas dielectric anisotropy is almost unchanged for both the nanocomposites. Threshold voltage for Freederick transition, switching voltage and splay elastic constant have decreased in the case of nanocomposite systems. Relaxation frequency and activation energy of an observed relaxation mode corresponding to molecular rotation about the short axis increase in the SmAd phases of both the nanocomposites. The optical study suggests that due to dispersion of nanoparticles,...
55 citations
TL;DR: In this paper, eight homologous series of 2-or 3-) substituted phenyl 4-alkoxy phenylazo (Ina-h) benzoates (ina−h) were prepared in which, within each homologously series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH3, H, F, Br and CN.
Abstract: Eight homologous series of 2- (or 3-) substituted phenyl 4ʹ-(4ʺ-alkoxy phenylazo) benzoates (Ina–h) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 6, 8, 10 and 12 carbons, while the other substituent, X, is a laterally attached polar group that alternatively changed from CH3, H, F, Br and CN. Compounds prepared were characterised by infrared and 1H-NMR spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and identified by polarised light microscopy. The results were discussed in terms of polarity and steric effects. The stability of the mesophase was correlated once with the dipolar anisotropy of the whole molecule and another with the dipolar anisotropy of the substituent, X. A comparative study was made between the investigated compounds and their previously prepared linear 4-substituted isomers, namely 4-substituted phenyl 4ʹ-(4ʺ-alkoxy phenylazo) benzoates (Ini–k).
TL;DR: The significance of Gray's cyanobiphenyls in the discovery of the partially bilayer smectic A phase (SmAd) and in the formulation of mixtures exhibiting the blue phase is described in this paper.
Abstract: The significance of Gray’s cyanobiphenyls in the discovery of the partially bilayer smectic A phase (SmAd) and in the formulation of mixtures exhibiting the blue phase is described. The properties of the SmAd phase and its relationships to molecular structures are reviewed. Induced phenomena such as the transformation of nematics into smectics, SmAd or SmA1, as well as the opposite transformation of smectics into nematics are described and discussed.
TL;DR: In this paper, a light shutter device using dye-doped cholesteric liquid crystals for a high-visibility see-through display was proposed, which can perfectly block the background image through simultaneous use of light scattering and absorption effects in a single-layered structure.
Abstract: We propose a light shutter device using dye-doped cholesteric liquid crystals for a high-visibility see-through display. In the focal-conic state, the proposed device can perfectly block the background image through simultaneous use of light scattering and absorption effects in a single-layered structure. By switching the proposed device placed at the backside of a see-through display, we can choose transparent or high-visibility display modes in a see-through display.
TL;DR: In this paper, the flexoelectric effect of a fringe field switching liquid crystal (LC) cell was investigated and the resultant image flicker with different LC mixtures at different frame rates.
Abstract: We investigated the flexoelectric effect of a fringe field switching liquid crystal (LC) cell and characterised the resultant image flicker with different LC mixtures at different frame rates. Incorporating with human eye perception of 10 observers, we found that LC mixtures with a dielectric anisotropy smaller than ~7 lead to unnoticeable image flicker at 60 frames per second. The obtained flicker sensitivity line serves as important guidelines for optimising LC materials and display devices.
TL;DR: In this paper, two new groups of azobenzene ester derivatives were synthesized: alkyl 4-(nonyloxy)phenyl]diazenyl]benzoates and 4-[4-(mene)diamyl]phenyl alkanoates, and the kinetic constants of the isomerization and relaxation processes were calculated.
Abstract: Two new groups of azobenzene ester derivatives were synthesised: alkyl 4-[4-(nonyloxy)phenyl]diazenyl]benzoates and 4-[4-(nonyloxy)phenyl]diazenyl]phenyl alkanoates. All 35 presented homologues are mesogenic. Moreover, some of the above-mentioned compounds exhibit rich liquid-crystalline polymorphism likewise tetramorphism. During this investigation by the use of polarising optical microscopy, differential scanning calorimetry and X-Ray studies, six types of mesophases were detected: nematic, smectics (A, C, I, F) and G. Furthermore, due to the presence of the photosensitive azo moiety, the E–Z isomerisation reaction is possible. This process, which is initiated by the UV irradiation, causes significant changes in the UV-Vis absorption spectra of investigated compounds. However, the photoisomerisation is a reversible process and in the dark the thermal relaxation of Z isomer takes place. Based on the achieved data, the kinetic constants of the isomerisation and relaxation processes were calculated. It sho...
TL;DR: In this article, five homologous series of 4-substituted phenyl 4′-(4″-alkoxy phenylazo) benzoates (Ina−−e) were prepared in which, within each homologic series, the length of the terminal alkoxy group varies between 8, 10, 12, 14 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH3O, CH3, H, Br and CN groups.
Abstract: Five homologous series of 4-substituted phenyl 4′-(4″-alkoxy phenylazo) benzoates (Ina–−e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed from CH3O, CH3, H, Br, and CN groups. Compounds prepared were characterised by infrared, mass, and H1-NMR spectroscopy and their mesophase behaviour investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The results were discussed in terms of mesomeric and polarisability effects. Only for the lower group of compounds, I8a-e, that showed a nematic phase, the nematic-to-isotropic transition temperatures (TN–I) were successfully correlated to the polarisability anisotropy of bonds to the substituent X. A comparative study was made between the investigated compounds and two previously prepared isomeric groups. In the first group of isomers, 4-(4′alkoxy phenylaz...
TL;DR: In this paper, an atomic force microscopy (AFM) study was conducted to examine the nanoscale morphology of the active layer without and after annealing at specific temperature.
Abstract: Advanced composite materials aimed for construction of organic photovoltaic cells have been studied by atomic force microscopy (AFM). The composites are based on poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM) and two different chiral photosensitive liquid crystalline (LC) materials. The objective of the study was to examine the nanoscale morphology of the active layer without and after annealing at specific temperature. The preliminary results of AFM observation of the morphological changes done on the investigated composites revealed an increase in the surface ordering. The surface area ratio decreases for both studied composites, while the basic roughness parameters (Sa and Sq) have been found toughly dependent on the structure of the photosensitive LC dopant.
TL;DR: In this paper, the effect of the size gradient distribution of liquid crystal (LC) droplets on the electro-optical and light-scattering properties of PDLC films was investigated.
Abstract: Polymer dispersed liquid crystal (PDLC) films with the size gradient of the LC droplets were prepared based on the epoxy/acrylate hybrid polymer matrix. The ultraviolet (UV) intensity gradient was induced by the UV-absorbing dye over the thickness of the samples. Taking advantage of the difference between the epoxy monomers and acrylate monomers in polymerisation rates and the UV intensity gradient, the gradient distribution of the LC droplet size was formed in PDLC films. The effect of the size gradient of the LC droplets on the electro-optical and the light-scattering properties of PDLC films was investigated. The results showed that due to the size gradient distribution of the LC droplets, PDLC films could exhibit the strong light scattering in the UV-visible-near infrared (VIS-NIR) region. Consequently, it provides a potential approach for modulating NIR light transmittance.
TL;DR: In this paper, the antiferroelectric smectic phase (SmCA*) with a direct transition from the antifroelectric to isotropic phase was observed, usually for propoxy-(CH2)3- spacing group.
Abstract: Novel chiral (S)-(+)-4ʹ-(1-methylalkoxycarbonyl)biphenyl-4-yl 4-[ω-(2,2,3,3,4,4,4-heptafluoro-butoxy)alkoxy]benzoates and 4-[ω-(2,2,3,3,4,4,4-heptafluorobutoxy)alkoxy]-2-fluorobenzoates were prepared using different optically active alcohols: (S)-(+)-2-hexanol, (S)-(+)-2-heptanol, (S)-(+)-2-nonanol, (S)-(+)-2-decanol, (S)-(+)-2-undecanol and (S)-(+)-5-methylhexan-2-ol. Properties, such as the sequence of phases, transition temperatures and enthalpies, were tested by polarising optical microscopy and differential scanning calorimetry. Extremely low melting compounds were found (below 10°C) for derivatives of (S)-(+)-2-hexanol. The antiferroelectric smectic phase (SmCA*) with a direct transition from the antiferroelectric to isotropic phase (SmCA*-Iso) was observed, usually for propoxy-(CH2)3- spacing group. Initially, multicomponent mixtures with broad temperature ranges of antiferroelectric phase and direct SmCA*-Iso transition were formulated.
TL;DR: A review of the impact of Professor Gray's nematic liquid crystals as well as the structures and functions of oligothiophene-based liquid crystals can be found in this article.
Abstract: It is fundamentally important to study the relationships between structures and properties of liquid crystals. Professor G.W. Gray developed new rod-like nematic liquid crystals, 4-alkyl- and 4-alkoxy-4ʹ-cyanobiphenyls, which act as materials for stable informational liquid crystal displays. This molecule was invented based on his deep understanding of the relationships of chemical structure and physical properties of liquid crystals. After the discovery of nematogenic liquid crystals for display application, the advent of the molecular design and synthesis of liquid crystals has produced a variety of new family of functional liquid crystals. For example, as a new twist of rigid rod mesogens, oligothiophene rings have emerged recently. Due to their extended π-conjugated systems, oligothiophene-based liquid crystals exhibit various electronic and optical functions. In this review, we describe the impact of Professor Gray’s nematic liquid crystals as well as the structures and functions of oligothiophene-ba...
TL;DR: In this article, the first examples of room temperature liquid crystal dimers based on cholesterol and pentaalkynylbenzene linked via flexible alkyl spacers were reported.
Abstract: In this article, we report the synthesis of the first examples of room temperature liquid crystal dimers based on cholesterol and pentaalkynylbenzene linked via flexible alkyl spacers. The thermal ...
TL;DR: In this paper, the spontaneous polarisation (Ps) values of a compound with a bulky chiral unit, zigzag ester linkage and polar fluorinated terminal were investigated.
Abstract: The electro-optical properties of orthoconic antiferroelectric liquid crystals of some analogues of (S)‑MHPOBC ((S)‑4‑(1‑methylheptyloxy)carbonylphenyl 4'-octyloxy-4-biphenylcarboxylate) have been investigated and discussed in terms of the structure property correlations of liquid crystalline molecules. Polarisation field reversal technique has been used for their characterisation. In this study the occurrence of such a high value of spontaneous polarisation (Ps) for the investigated compound is especially noteworthy as they comprise a bulky chiral unit, zigzag ester linkage and polar fluorinated terminal. Lengthening of oligomethylene spacer in the terminal chain and placement of fluorine atom in the molecular core structure leads to reduction in the value of Ps. The Ps data suggest that the nature of the chiral smectic C (SmC*) to smectic A (SmA) phase transition is of second order and the critical exponent β is in the range 0.19–0.34. The ‘V-shaped’ mode or thresholdless switching in such high-polarisa...
TL;DR: In this paper, six new compound derivatives from thiophene were synthesised, including three symmetrical and three non-symmetrical compounds, and the structural modifications were made by changing the number of alkoxy groups in order to understand the relation between structure and mesomorphic behaviour.
Abstract: In this work, six new compound derivatives from thiophene were synthesised. The three symmetrical compounds were synthesised containing two heterocyclic 1,2,3-triazole on each side of thiophene, 2,5-disubstituted and the three non-symmetrical compounds were synthesised containing alkyne groups as a spacer in replacing one of these heterocycles. The structural modifications were made by changing the number of alkoxy groups in order to understand the relation between structure and mesomorphic behaviour. Some of the compounds presented liquid crystalline properties, smectic and nematic mesophases. The non-symmetrical compounds allowed for a low emission in the blue region.
TL;DR: In this article, the effect of lateral methyl substitution on the mesophase behavior of the previously investigated laterally neat 4-substituted phenyl 4-methyl-4-alkoxyphenylazo) benzoates (Ina-e) was investigated.
Abstract: In order to investigate the effect of lateral methyl substitution on the mesophase behaviour of the previously investigated laterally neat 4-substituted phenyl 4ʹ-(4ʺ-alkoxyphenylazo) benzoates (Ina–e), five homologous series of 4-substituted phenyl 4ʹ-(3ʺ-methyl-4ʺ-alkoxyphenylazo) benzoates (IIna–e) were prepared in which, within each homologous series, the length of the terminal alkoxy group varies between 8, 10, 12, 14, and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed between the electron-donating CH3O and CH3 groups, and the electron-withdrawing Br and CN groups, in addition to the unsubstituted analogue. Two other isomeric series (IIIna–e) were also prepared in which the methyl group is laterally attached, this time, to position 2 of the same ring, aiming to investigate the effect of the different orientation of the methyl groups on the mesophase behaviour of the produced isomers. The results were discussed in terms of steric, mesomeric, and polari...
TL;DR: In this paper, the role of bend elastic constants and field effects in the stability of the blue phase monodomains has been discussed, and the dependence of these phenomena on the physical properties of the liquid crystalline system, including the twist and bend elastic constant and the dielectric anisotropy, is emphasised.
Abstract: The blue phases are fascinating structures in liquid crystals, fluids that exhibit cubic structures that have true crystalline order. The blue phases were discovered in the 1970s and were the subject of extensive research in the 1980s, when a deep understanding of many of their properties was established. The discovery that the blue phases could be stabilised to exist over wide temperature ranges meant that they became more than scientific curiosities and led to a recent resurgence in research into them as they offer some promise in applications. This paper considers some important aspects of the blue phases that are recurrent topics in their research. It describes factors affecting blue phase stability, demonstrating on the role of the bend elastic constant; field effects, including the Kerr effect, electrostriction and relaxation phenomena; and alignment, in particular production and control of blue phase monodomains. The dependence of these phenomena on the physical properties of the liquid crystalline system, including the twist and bend elastic constants and the dielectric anisotropy, is emphasised wherever possible. The paper links work carried out in the 1980s with contemporary research, using a few key examples to show how there is still much to understand in this beautiful topic.
TL;DR: In this article, the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy.
Abstract: Four new groups of the di-fluoro-substituted 4-(2′-(or 3′)-fluoro phenylazo)-2-(or 3-) fluoro phenyl-4″-alkoxyphenylazo benzoates (In–IVn) were prepared and investigated for their mesophase behaviour. An alkoxy group of variable chain length (n = 6, 10 and 14 carbons) is attached to the terminal phenylazo benzoate moiety, and two lateral fluoro substituents are attached individually with different orientations to the other two adjacent rings. The molecular structures of the prepared compounds were confirmed by Fourier transform infrared spectroscopy and 1H NMR spectroscopy. The study aims to investigate the steric effect of the spatial orientation and relative positions of the two lateral fluorine atoms on the mesomorphic properties in their pure states. The mesophase behaviour was investigated via differential scanning calorimetry and mesophases were identified by polarised light microscopy. The investigation shows that these compounds exhibit high enantiotropic mesophases (SmC and N) and broad mesophase...
TL;DR: In this paper, the phase transitions and physical properties of colloidal suspensions of BaTiO3 nanoparticles and two cyanobiphenyl liquid crystals (4-pentyl-4-4ʹ-cyanobiphensyl and 4-octyl- 4-4 -cyclophosphate-cyclophenyl) were investigated.
Abstract: We report experimental studies on the phase transitions and physical properties of colloidal suspensions of BaTiO3 nanoparticles and two cyanobiphenyl liquid crystals (4-pentyl-4ʹ-cyanobiphenyl and 4-octyl-4ʹ-cyanobiphenyl). From the differential scanning calorimetric measurements, we show that the nanoparticles have antagonistic effect on the isotropic to nematic and nematic to smectic-A phase transitions. The birefringence, dielectric anisotropy and splay elastic constant remain almost unchanged, whereas the bend elastic constant and rotational viscosity decrease considerably. The experimental results are discussed based on the possible contribution of BaTiO3 nanoparticles and free surfactant molecules in the suspensions.
TL;DR: In this article, an in-plane driven liquid crystal (LC) device with a crossed polariser has been proposed for flexible liquid crystal displays, which shows a very high contrast ratio over 1000 comparable to the conventional nematic inplane switching cell, wide viewing angle, low threshold voltage of 8.2
Abstract: Optically isotropic liquid crystal (OILC) mixtures utilising polymerisation-induced phase separation in mixtures of prepolymers and liquid crystals (LCs) have been made and their overall electro-optic performances have been tested by applying an in-plane electric field for flexible display application. Excellent transparent films with a LC to prepolymer weight ratio of 42:58 are achieved and confirmed by SEM images. The average LC droplet size inside the polymer matrix is 215 nm. Consequently, an in-plane driven LC device with a crossed polariser shows a very high contrast ratio over 1000 comparable to the conventional nematic in-plane switching cell, wide viewing angle, a low threshold voltage of 8.2 V, hysteresis free and fast response time. The proposed LC device is free from an alignment layer and the rubbing process and its dark state is not disturbed by mechanical pressure, which can open its application to flexible liquid crystal displays.
TL;DR: In this article, the authors demonstrate a simple method for measuring the twist elastic constant (K22) of a nematic liquid crystal (LC) by adding some chiral dopant to an LC host, the LC directors rotate 180° in a homogeneous cell, known as 180° super-twisted nematic (STN) cell.
Abstract: We demonstrate a simple method for measuring the twist elastic constant (K22) of a nematic liquid crystal (LC). By adding some chiral dopant to an LC host, the LC directors rotate 180° in a homogeneous cell, which is known as 180° super-twisted nematic (STN) cell. By preparing two such STN cells with different chiral concentrations and measuring their Freedericksz threshold voltages, we can obtain the K22 and helical twisting power simultaneously. In the whole process, there is no need to measure the pitch length. Our obtained K22 values agree well with those reported by using other methods.
TL;DR: In this paper, the dependence of relaxation frequency on molecular structures and physical properties of systems (molecular rigid core length, polarity and viscosity) is discussed and a mixture of two, three and four fluoro-substituted in the lateral position tolanes and phenyltolanes showing negative dielectric anisotropy is presented.
Abstract: Relaxation frequencies fr characterising the molecular rotation around the short axes (flip-flop movement) of 45 three- and four-ring polar compounds with high birefringence (mainly cyclohexyl, phenyl and biphenyl tolanes and quaterphenyls terminated with F, OCF3, NCS group) have been measured. These compounds exhibit a large positive dielectric anisotropy Δe = e║ − e⊥ in the nematic phase and relatively low fr values (in the range of dozens kHz). The dependence of fr upon molecular structures and physical properties of systems (molecular rigid core length, polarity and viscosity) is discussed. Mixtures for dual frequencies addressing display with the crossover frequency fco of the order of ~1 kHz have been prepared by joining the above compounds with a mixture consisted of two, three and four fluoro-substituted in the lateral position tolanes and phenyltolanes showing negative dielectric anisotropy. It was stated that relaxation frequency is correlated mainly with their length and polarity.