Showing papers in "Liquid Crystals in 2012"
TL;DR: In this paper, seven members of the bis(ω-(cholesteryloxycarbonyl)alkyl) disulfides, which contain a sulfur−sulfur link in the flexible spacer have been synthesized and their liquid crystal properties characterised.
Abstract: Seven members of the homologous series of the liquid crystal dimers, the bis(ω-(cholesteryloxycarbonyl)alkyl)disulfides, which contain a sulfur−sulfur link in the flexible spacer have been synthesised and their liquid crystal properties characterised. The dimers are referred to using the acronym Chol-n-SS-n-Chol in which n denotes the number of carbon atoms linking the cholesteryl-based groups and the sulfur atoms, and was varied between 3, 5, 6, 8, 10, 11 and 12. All seven homologues exhibit a chiral nematic phase and for the longest three members a smectic A phase was also observed. An odd−even effect is apparent in both the transition temperatures and the values of the entropy change associated with the chiral nematic−isotropic transition, ΔSN*I /R, in which dimers with even values of n show the higher values. This is interpreted in terms of the average molecular shapes in which the C−S−S−C dihedral angle is around 90°. The values of ΔSN*I/R shown by these dimers are very small for liquid crystal dimer...
122 citations
TL;DR: The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the α-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-ω-(4-methioxazobenzene-4'-oxy)alkanes as discussed by the authors.
Abstract: The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the α-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-ω-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic–isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the α,ω-bis(4-methoxyazobenzene-4'-oxy)alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic–isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-...
118 citations
TL;DR: The structure/property relationship of two classes of synthetic branched-chain glycolipids, namely the Guerbet and isoprenoid glycosides, are presented, in particular highlighting the importance of chain branching to their self-assembly properties.
Abstract: This review presents the structure/property relationship of two classes of synthetic branched-chain glycolipids, namely the Guerbet and isoprenoid glycosides, in particular highlighting the importance of chain branching to their self-assembly properties. Alkyl chain branching in glycolipids tends to stabilise the reversed type phases as well as a lamellar (Lα) phase. These glycolipids exhibit several reversed bicontinuous cubic phases ( ), the reversed hexagonal phase (H II) and the lamellar phase. The detailed structures of the phases are governed by the balance between the hydrophobic chain bulkiness and the headgroup interaction, including hydrogen bonding. Among the isoprenoid glycolipids, an aqueous isoprenoid xyloside exhibits a bicontinuous cubic phase with a diamond (Pn3m) space group at full hydration and that of a glucoside adopts the stable reversed micellar cubic phase of an Fd3m space group. In the series of Guerbet glycolipids, the ones with longer chains may form stable bicontinuous cubic p...
92 citations
TL;DR: In this paper, the authors proposed a merit of using a liquid crystal with negative dielectric anisotropic anisotropy for the fringe-field switching (FFS) mode.
Abstract: The fringe-field switching (FFS) mode has been widely applied in high-resolution portable liquid crystal displays because of its excellent performances in transmittance, viewing angle, and operating voltage. Up to now, the FFS mode utilised a liquid crystal with positive dielectric anisotropy owing to fast response time and low operating voltage. This paper proposes a merit of using a liquid crystal with negative dielectric anisotropy. The optimised cell structures with thin cell gap and fine patterned electrode structures make the FFS mode with negative liquid crystals exhibit higher transmittance than that of the positive liquid crystals and a fast response time.
74 citations
TL;DR: In this article, the bending angles of the five-membered heterocyclic substituents are crucial in determining the thermal stability of the LC phases formed, indicating a delicate balance of forces involved in LC phases.
Abstract: New fluorescent liquid crystalline (LC) compounds containing the 2,1,3-benzothiadiazole chromophore as the central core substituted with 1,2,4-oxadiazole, 1,2,3-triazole and 1,2-isoxazole heterocycles were synthesised and their mesophases characterised by polarised optical microscopy, differential scanning calorimetry and X-ray diffraction. We observed that the bent angles of the five-membered heterocyclic substituents are crucial in determining the thermal stability of the LC phases formed, indicating a delicate balance of forces involved in LC phases. The mesophases formed by all symmetrical and unsymmetrical compounds showed thermal stability in the order 1,2-isoxazole > 1,2,3-triazole > 1,2,4-oxadiazole.
67 citations
TL;DR: Polarizing optical microscopy (POM) shows evidence for a reversible uniaxial nematic (NU) to biaxially nematic phase transition in a quiescent melt of bent-core mesogens (BCM) as discussed by the authors.
Abstract: Polarising optical microscopy (POM) shows evidence for a reversible uniaxial nematic (NU) to biaxial nematic (NB) phase transition in a quiescent melt of bent-core mesogens (BCM). A second superimposed Schlieren texture, attributed to a second director field, grows into the NU phase on lowering the temperature and disappears again on heating, indicating a fully reversible NB to NU phase transition. This POM result together with recent X-ray data provides a new signature for the NB phase in this class of BCMs, and offers a new method for assessment of new biaxial nematic phases.
55 citations
TL;DR: In this paper, five bent-shaped molecules derived from the 1,3,4-oxadiazole core are synthesized and doped into chiral nematic liquid crystals to induce the blue phase.
Abstract: Five bent-shaped molecules derived from the 1,3,4-oxadiazole core are synthesised and doped into chiral nematic liquid crystals to induce the blue phase. The effects of their terminal chain length on the blue phase range are compared and analysed experimentally. The results show that the blue phase range is significantly influenced by terminal chain length, and the widest range could be obtained in the case that the chain length is neither too long nor too short. In addition, it is also found that the mechanism of a blue phase induced by bent-shaped molecules is mainly related with its geometry, no matter whether a liquid crystal phase exists or not.
51 citations
TL;DR: In this paper, the first discotic liquid crystals were prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or trans-4-alkoxy-4′-stilbazoles.
Abstract: New discotic nematic liquid crystals have been prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) and the peripheral molecules of stilbazole derivatives. The various nematic phases formed by new hydrogen bonding building blocks were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The first discotic complexes of PG and trans-4-alkoxy-4′-stilbazoles exhibited nematic columnar (NC) and hexagonal columnar phases depending on the length of alkyl chains, which were considered as the basic discotic structure. Several structural variations on the building blocks were attempted to examine their effects on the liquid crystalline properties of discotic complexes. The nematic lateral phase (NL) with enhanced intercolumnar order was observed for the complexes of PG and trans-4-cyanoalkoxy-4′ stilbazoles due probably to the strong dipole interactions between...
46 citations
TL;DR: A series of novel 1,3,5-triazine-based triphenylene oligomers 7, 10 and 12 with large bridging polyaromatic core were designed and synthesized by simple procedures in high yields as mentioned in this paper.
Abstract: Series of novel 1,3,5-triazine-based triphenylene oligomers 7, 10 and 12 with large bridging polyaromatic core were designed and synthesised by simple procedures in high yields. Their structures were confirmed by FTIR, 1H NMR, ESI-MS and elemental analyses. Their mesomorphic behaviours were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. 1,3,5-triazine-based triphenylene monomer 7 has no mesomorphic property, but 1,3,5-triazine-based triphenylene dimer 10 and 1,3,5-triazine-based triphenylene trimer 12 possess excellent mesomorphic properties. The mesomorphic temperature range of compound 12 was as wide as 180°C. These studies indicated that the mesomorphic properties were determined by the numbers of triphenylene units. More units of triphenylene in the oligomers resulted in better mesomorphic properties.
46 citations
TL;DR: A series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different rigid cores were synthesized under the microwave irradiation based on green chemistry and atom economy as mentioned in this paper.
Abstract: A series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different rigid cores were synthesised under the microwave irradiation based on green chemistry and atom economy. The induced blue phase (BP) behaviours of these bent-shaped compounds were investigated after blending them with a high twisted power chiral dopant or doping them into the chiral nematic liquid crystal (N*LC). It was found that the BP ranges varied greatly with the difference in the rigid cores of 2,5-disubstituted 1,3,4-oxadiazoles, and the bent-shaped molecules with higher miscibility and twisted molecular conformation significantly contribute to the stabilisation of BPs. In addition, the electro-optical performances of pure BPs and polymer-stabilised BPs in the systems containing 1,3,4-oxadiazoles with different rigid cores were also explored, which shows that the Kerr constant decreases after being polymerised and varies with the doping of the compounds possessing different rigid cores in the polymerised mixtures.
43 citations
TL;DR: In this paper, the effects of monomer structure on the morphology of polymer networks in PDLC films were studied and the effect of morphology of the polymer network on the electro-optical properties of PDLC was also investigated.
Abstract: Polymer-dispersed liquid crystal (PDLC) films were prepared by photochemical polymerisation with a series of (meth)acrylate monomers. The effects of monomer structure on the morphology of polymer networks in the PDLC films were studied. The acrylate monomers without sidegroup chain formed uniform polymer networks. The methacrylate monomers with methyl as their sidegroup chains formed lace-like networks. The size of the LC droplets increased with increasing the length of the flexible chain of both methacrylate and acrylate monomers. Meanwhile, the effects of the morphology of the polymer network on the electro-optical properties of PDLC films were also investigated.
TL;DR: In this article, the biaxial nematic phase domain is present in a window of values of, where is the number of carbon atoms in the alkyl chain of KL.
Abstract: Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K2SO4)/alcohol (n-OH)/water, with the alcohols having different numbers of carbon atoms in the alkyl chain ( ), from 1-octanol to 1-hexadecanol, were investigated by optical techniques (optical microscopy and laser conoscopy). The biaxial nematic phase domain is present in a window of values of , where is the number of carbon atoms in the alkyl chain of KL. The biaxial phase domain became smaller and the uniaxial-to-biaxial phase transition temperatures shifted to relatively higher temperatures upon going from 1-nonanol to 1-tridecanol. Moreover, compared with other lyotropic mixtures these new mixtures present high birefringence values, which we expect to be related to the micellar shape anisotropy. Our results are interpreted assuming that alcohol molecules tend to segregate in the micelles in a way that depends on the relative value of n with respect to . The larger the value of n, the more alcohol molecules...
TL;DR: In this paper, a new method for the synthesis of 4'-alkyl-, 4'alkyl-cyclohexyl or 4',alkylphenyl monofluoro-, difluoro- and tetrafluoro -substituted 4-alkoxy- or 4-alkyltolanes is proposed.
Abstract: Convenient new methods for the synthesis of 4'-alkyl-, 4'-alkylcyclohexyl or 4'-alkylphenyl monofluoro-, difluoro- and tetrafluoro-substituted 4-alkoxy- or 4-alkyltolanes are proposed. The temperature and enthalpy of the phase transition for the homologues of the eight series, as well as the examples of the mixtures with negative dielectric anisotropy (Δϵ < −5) and high birefringence (Δn ≥ 0.3), are given.
TL;DR: The mesomorphic properties of these compounds were studied by differential scanning calorimetry and polarising optical microscopy as mentioned in this paper, and the best results were obtained with compounds of series 3a-f.
Abstract: Novel liquid crystal materials base on amino-thiadiazoles, specifically 5-(3,4-di-, and/or 3,4,5-tri-n-alkoxy)phenyl-2-amino-1,3,4-thiadiazoles (3a–f, n = 10, 12, 14) and 5-(3,4-di- and/or 3,4,5-tri-n-alkoxy)phenyl-2-(4-amino)phenyl-1,3,4-thiadiazoles (6a–f, n = 10, 12, 14) were synthesised. The mesomorphic properties of these compounds were studied by differential scanning calorimetry and polarising optical microscopy. All the compounds in series 3a–f and series 6a–f display an enantiotropic columnar phase. The mesomorphic properties were found to be dependent on the number of the side alkoxy chains, and on the length of the rigid core, and on the position of the thiadiazole ring. The best results were obtained with compounds of series 3a–f.
TL;DR: The refractive indices of p(p-ethoxyphenylazo) phenyl (EPAP) alkanoates, which are the nematic liquid crystals where the alkyl chain n is 5, 6, 7 and 11, were measured using a wedge technique.
Abstract: The refractive indices of p(p-ethoxyphenylazo) phenyl (EPAP) alkanoates, which are the nematic liquid crystals where the alkyl chain n is 5, 6, 7 and 11, were measured as a function of temperature at λ = 6328 A using a wedge technique. The temperature variation of the orientational order parameter (S) is calculated at this wavelength using the Vuks model (with consideration of internal field) and by different methods excluding the internal field – Haller and Kuczynski models, and involving effective geometry parameter (αg). The intensity of light deflection in a uniaxial EPAP alkanoate with a particular molecular configuration and ordering by varying temperature is discussed. The temperature gradients of the ordinary (∂no /∂T) and extraordinary (∂ne /∂T) refractive indices are analysed. Due to a high clearing temperature with low molecular chain length, EPAP valerate exhibited low deviation of light with a large positive value of ∂no /∂T.
TL;DR: In this paper, the authors have doped reverse morphology polymer dispersed liquid crystal (PDLC) films with increasing amounts of single-walled carbon nanotubes and investigated their effects on the morphology, electro-optical properties, and conductivity of the PDLC films.
Abstract: 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.
TL;DR: In this paper, multi-walled carbon nanotubes were dispersed at low concentrations into various achiral liquid crystals having either a thioester or oxoester linkage group in the core.
Abstract: Multi-walled carbon nanotubes were dispersed at low concentrations into various achiral liquid crystals having either a thioester or oxoester linkage group in the core. The presence of the carbon nanotubes resulted in chiral signatures being observed in the liquid crystals, including an electroclinic effect (a rotation of the liquid crystal director perpendicular to, and linear in, an applied electric field) in both the nematic and smectic A phases, and a macroscopic helical twist of the liquid crystal director in the nematic phase. For both experiments the chiral signatures for the thioester liquid crystals were found to be an order of magnitude larger than those of the oxoesters. We speculate that the much larger strength of the thioester's chiral properties is a result of stronger non-covalent interactions between the liquid crystal molecule and carbon nanotube.
TL;DR: Aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent as mentioned in this paper.
Abstract: A simple and efficient procedure for the synthesis of a new class of organoselenium liquid crystal compounds was developed. The coupling of aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent. This is the first report of the synthesis and characterisation of liquid crystal-based diselenides. Their mesophases were characterised by polarising optical microscopy and differential scanning calorimetry. Compounds 1, 2 and 4b exhibited the smectic A phase. In addition, these compounds showed weak blue fluorescence in solution (λmax. em. 350–405 nm) and a Stokes shift of around 90 nm.
TL;DR: In this paper, the electro-rheological behavior of a series of four liquid crystal (LC) cyanobiphenyls with a number of carbon atoms in the alkyl group, ranging from five to eight (5CB-8CB), was studied.
Abstract: In this work we study the electro-rheological behaviour of a series of four liquid crystal (LC) cyanobiphenyls with a number of carbon atoms in the alkyl group, ranging from five to eight (5CB–8CB). We present the flow curves for different temperatures and under the influence of an external electric field, ranging from 0 to 3 kV mm−1, and the viscosity as a function of the temperature, for the same values of electric field, obtained for different shear rates. Theoretical interpretation of the observed behaviours is proposed in the framework of the continuum theory of Leslie–Ericksen for low molecular weight nematic LCs. In our analysis, the director alignment angle is only a function of the ratio between the shear rate and the square of the electric field – boundary conditions are neglected. By fitting the theoretical model to the experimental data, we are able to determine some viscosity coefficients and the dielectric anisotropy as a function of temperature. To interpret the behaviour of the flow curves...
TL;DR: In this article, a family of 4'-(ω-perfluoroalkanoyloxy)alkoxybiphenyl-4-yl (S)-4-(1-methylheptyloxy)benzoates smectic liquid crystals were synthesized in search of new compounds with a high-tilted C* phase.
Abstract: The aim of our research was the preparation of a family of 4'-(ω-perfluoroalkanoyloxy)alkoxybiphenyl-4-yl (S)-4-(1-methylheptyloxy)benzoates smectic liquid crystals. The synthesis has been designed in search of new compounds with a high-tilted smectic C* phase. Five homologous series of chiral esters have been obtained. Phase transition temperatures and enthalpies for all compounds, as well as tilt angle, spontaneous polarisation, helical pitch and layer thickness for some, have been measured. The shapes of the molecules were also simulated. Relationships between the chemical structure and the observed physical and chemical properties are discussed. Unexpectedly, the compounds show a low-tilt smectic C* phase, and sometimes also a smectic C*A phase; an explanation of this feature is given.
TL;DR: In this paper, the texture analysis of thermotropic liquid crystals was carried out using a polarising optical microscope under crossed polarisers attached with a hot stage and a high-resolution camera.
Abstract: Analysis of the textures and phase transitions of thermotropic liquid crystals p-ethoxybenzylidene-p-n-butylaniline, cholesteryl myristate and cholesteryl decanoate was carried out using a polarising optical microscope under crossed polarisers attached with a hot stage and a high-resolution camera. Using MATLAB software, the statistical parameters, such as mean, standard deviation, root mean square, contrast and entropy of the textures as a function of temperature, are computed. These results show abrupt changes as a function of temperature, indicating the phase transition of the sample. The statistical image analysis of various liquid crystal samples are in good agreement with the literature results and the proposed methodology offers a reliable and very sensitive technique to identify mesophase transition temperatures.
TL;DR: In this paper, the mesophase behavior of pyridine-based azo dyes was investigated by differential scanning calorimetry and polarised light microscopy, and the structures of compounds were confirmed via elemental analyses, IR, 1H-NMR and mass spectra.
Abstract: Two types of new pyridine-based azo dyes, namely, 4-(3′-pyridylazo)-4″-alkoxybenzoates with various alkoxy chains and 4-(3′-pyridylazo)-4″-substituted benzoates bearing groups of different polarities, were prepared and investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. All homologues of the former group were found to be mesomorphic, while all derivatives of the latter are non-mesomorphic. The structures of compounds prepared were confirmed via elemental analyses, IR, 1H-NMR and mass spectra. Four types of angular 1:1 hydrogen-bonded supramolecular complexes were prepared via hydrogen-bond formation between each of the pyridine-based derivatives and two types of benzoic acids, namely, 4-alkoxy and 4-substituted benzoic acids. The latter bear the polar groups (CH3O, CH3, Br and NO2) in addition to benzoic acid. Complexes were similarly investigated and it was found that three of them are mesomorphic while the fourth is not. The formation of 1:1 hy...
TL;DR: In this paper, a fluorinated compound, (S)-4′′-(6-perfluoropentanoyoxyhexylhexyl-1-oxy)-2′,3′-difluoro-4-(1-methylheptyloxycarbonyl)-[1,1′:4′, 1′]-terphenyl, has been investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and frequency-dependent dielectric spectroscopy methods.
Abstract: The fluorinated compound, (S)-4′′-(6-perfluoropentanoyoxyhexyl-1-oxy)-2′,3′-difluoro-4-(1-methylheptyloxycarbonyl)-[1,1′:4′,1′′]-terphenyl, which exhibits antiferroelectric SmCA*, ferroelectric SmC* and paraelectric SmA* phases, has been investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and frequency-dependent dielectric spectroscopy methods. X-ray studies have revealed that the layer thickness remains almost constant in the SmA* phase but within the SmC* and SmCA* phases it decreases with decreasing temperature, a step jump being observed only at the SmA*–SmC* transition. The tilt angle in the SmCA* phase decreases from 22.2° to 19.5°, and in the SmC* phase it decreases from 18.8° to 5.5°. Spontaneous polarisation is found to be quite high and varies between 74.1 and 118.7 nC cm−2. The variation in e′ and e′′ with temperature shows a discontinuous change at the transition temperatures. Goldstone mode relaxation is only observed in the ferroelectric and an...
TL;DR: In this paper, a new dinaphthylacetylene liquid crystal (LC) compound with alkoxy tails of length m (DNA-OCm) was synthesized and characterised their phase behavior by polarising optical microscopy and differential scanning calorimetry, where all compounds exhibited a nematic phase.
Abstract: We synthesised 1,2-bis(6-alkoxy-2-naphthyl)acetylene as a new dinaphthylacetylene liquid crystal (LC) compound with alkoxy tails of length m (DNA–OCm) and characterised their phase behaviour by polarising optical microscopy and differential scanning calorimetry, where all compounds exhibited a nematic phase. Also, we measured the actual, and not extrapolated, Δn values of this target compound, and our results show the birefringence potential of the pure LC compound. They have high birefringence values, with the highest value of approximately 0.5 obtained for DNA–OC2 at 550 nm at 10°C above the nematic−crystal transition temperature.
TL;DR: In this paper, a series of non-symmetric chiral isoflavone-based liquid crystalline dimers, α-(2-methylbutyl-4′-(4″-phenyloxy)benzoate)-ω-(3-(4′-decyloxyphenyl)-4H-1-benzopyran-4-one-7oxy)alkanes, with 3-12 carbon atoms in the alkyloxy spacer, have been synthesized.
Abstract: A new series of non-symmetric chiral isoflavone-based liquid crystalline dimers, α-(2-methylbutyl-4′-(4″-phenyloxy)benzoate)-ω-(3-(4′-decyloxyphenyl)-4H-1-benzopyran-4-one-7-oxy)alkanes, with 3–12 carbon atoms in the alkyloxy spacer, have been synthesised. A pronounced odd–even effect for the phase transition temperatures upon varying the spacer length was observed. The short dimers exhibited monolayer smectic A (SmA) and smectic C (SmC*) phases while for longer homologues a chiral nematic (N*) phase was found. The temperature range of the nematic phase was broadened with elongation of the alkyl spacer. Stabilisation of the nematic phase resulted from competition between the monolayer and intercalated smectic structures. The SmA–SmC* phase transition was second order for all studied compounds with a cross over to the de Vries type behaviour for the shortest homologue.
TL;DR: In this paper, octadecyltrichlorosilane (OTS) was added to the liquid crystal (LC) mixture for vertical alignment without using an alignment layer printing process, and the OTS-LC system exhibited a more stable LC alignment compared with the polyhedral oligomeric silsesquioxane (POSS) -LC system.
Abstract: Here, we demonstrate excellent liquid crystal (LC) vertical alignment without using an alignment layer printing process by introducing octadecyltrichlorosilane (OTS) into the LC mixture. Further, we investigated the alignment mechanism by analysing the surfaces of the substrates. The optimum concentration of OTS was found to be about 0.03 wt%, which is 1/100 of that in the previously reported polyhedral oligomeric silsesquioxane (POSS)–LC system. Moreover, the OTS–LC system exhibited a more stable LC alignment compared with the POSS–LC system. These differences may arise from the different strengths of surface–dopant interactions; that is, the covalent bond in the OTS–LC system and the van der Waals interactions in the POSS–LC system. We also demonstrated that the method can be used in a capillary tube, which may serve as a new method facilitating the application of LCs with curved surfaces.
TL;DR: In this article, a series of o-diamidobenzenes, bearing long-chain alkyl substituted gallic ester groups, have been synthesised, and the liquid crystalline phases spread over phase width of extremely wide temperature intervals from -50 to 118°C.
Abstract: Two series of o-diamidobenzenes, bearing long-chain alkyl substituted gallic ester groups, have been synthesised. The 3,4,5,6-unsubstituted amides 7 with a minimum chain length of C9 exhibited columnar rectangular mesophases of p2mm symmetry with Z = 2. The liquid crystalline phases spread over phase width of extremely wide temperature intervals from -50 to 118°C. However, the phase width slightly decreased with an increase in the length of alkyl substituents. Despite their very similar molecular structure, 1,2-dimethoxy-4,5-diamides 10 revealed a different packing behaviour in their mesophases, due to steric factors. The diamides 10 formed columnar rectangular mesophases with p2mm symmetry, but with Z = 3. In a comparison with unsubstituted analogues 7, compounds 10 displayed even broader mesophases (with temperature intervals up to 220°C).
TL;DR: In this article, the UV polymerisation temperature dependence of the microstructure and the electro-optical properties of PDLC films based on epoxies/acrylates hybrid polymer matrix components were studied.
Abstract: Hybrid polymers, which form a combination of monomers with different reactive groups and curing mechanisms, synergistically combine the properties of the two constituent homopolymers. In this paper, polymer-dispersed liquid crystal (PDLC) films using epoxies / acrylates as hybrid polymer matrix components were prepared. The UV polymerisation temperature dependence of the microstructure and the electro-optical properties of PDLC films based on epoxies / acrylates hybrid polymer matrix had been studied. The electro-optical properties of PDLC films depend strongly on the liquid crystal (LC) domain size and morphology of PDLC films, which could be controlled by the polymerisation rate of the curable monomers and the diffusion rate of the LC molecules during the film preparation process. The polymerisation rate of the curable monomers and the diffusion rate of the LC molecules depend exponentially on the UV polymerisation temperature. Therefore, this research reports an example of methods to prepare PDLC films...
TL;DR: In this article, the electro-optic properties of a Y2O3 nanoparticle-doped nematic liquid crystal (NLC) system were investigated and shown to have superior EO properties.
Abstract: We report the electro-optic (EO) characteristics of a Y2O3 nanoparticle-doped nematic liquid crystal (NLC) system. After doping with 2 wt.% Y2O3 nanoparticles, LC alignment shows a homogeneous orientation state without aggregation and crack. In particular, the pretilt angle was slightly increased in proportion to Y2O3 doping concentration. Response time was improved by nearly 53%, and the threshold voltage for display operation was reduced from 4.2 V to 2.6 V. We assumed that superior EO properties were achieved by the Y2O3 nanoparticle, which reduces the field-screening effect of impurity ions. We also confirmed that enhanced EO characteristics were achieved without loss of light transmittance.
TL;DR: In this paper, the synthesis of chiral liquid crystal monomers (M1 −M4 ) derived from menthyl groups, the corresponding smectic polymers (P1 −P4 ), and cholesteric elastomers (E1 −E4 ) based on M2 and crosslinking agent (CA ) is presented.
Abstract: The synthesis of new chiral liquid crystal monomers (M1 −M4 ) derived from menthyl groups, the corresponding smectic polymers (P1 −P4 ), and cholesteric elastomers (E1 −E4 ) based on M2 and crosslinking agent (CA ) is presented. The chemical structures and purity were characterised by Fourier transform infrared, 1H nuclear magnetic and elemental analyses. The phase behaviour and mesomorphism were investigated by differential scanning calorimetry, polarising optical microscopy, thermal gravimetric analysis and X-ray diffraction. The selective reflection of light for M1 −M4 was characterised with ultraviolet/visible/near infrared. The structure–property relationships of M1 −M4 and P1 −P4 were studied. The effect of the content of mesogenic crosslinking units on phase behaviour and mesomorphism of E1 −E4 was discussed. By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, M1 −M4 all showed strong mesomorphism and exhibited an oily streak and focal conic textures of the ch...