Showing papers in "Liquid Crystals in 2006"
TL;DR: In this paper, the behavior of the anisotropic electrical conductivity of liquid crystal-gold nanoparticle (LC-GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol-capped GNPs has been investigated.
Abstract: The behaviour of the anisotropic electrical conductivity of liquid crystal–gold nanoparticle (LC‐GNP) composites consisting of a commercially available room temperature nematic compound doped with alkylthiol‐capped GNPs has been investigated. The nematic–isotropic transition of the composite decreases nearly linearly with increasing X, the concentration of GNP (in weight %) at a rate of about 1°C /weight %. The inclusion of GNPs increases the electrical conductivity of the system with the value increasing by more than two orders of magnitude for X = 5%. However, the anisotropy in conductivity, defined as the ratio of the conductivity along (σ∥) and orthogonal (σ⊥) to the director shows a much smaller but definite decrease as X increases.
124 citations
TL;DR: In this article, non-symmetric dimeric liquid crystals have been studied in the context of engineering and physical sciences at the University of Aberdeen in the UK, where the paper is based on the work of Rigeme et al.
Abstract: CORRIE T. IMRIE* School of Engineering and Physical Sciences, Meston Building, University of Aberdeen, Old Aberdeen, Scotland, UK A Commentary on the paper “Non‐symmetric dimeric liquid crystals. T...
121 citations
TL;DR: In this paper, a general synthetic strategy based on a convergent approach allowed a series of luminescent unsymmetrical bent core compounds (2,5−(disubstituted)−1,3,4−oxadiazole derivatives) via the Sonogashira crosscoupling reaction, all possessing a similar hockey stick shape.
Abstract: A general synthetic strategy, based on a convergent approach, allowed us to prepare a series of luminescent unsymmetrical bent‐core compounds (2,5‐(disubstituted)‐1,3,4‐oxadiazole derivatives), via the Sonogashira crosscoupling reaction, all possessing a similar hockey stick shape. Their mesophases were characterized using polarizing optical microscopy and differential scanning calorimetry. The observed LC phases possess the classical textures of calamitic liquid crystals. Fluorescence in solution for these compounds exhibits strong blue emission (λmax em. = 390–460 nm) with good quantum yields (50–85%).
100 citations
TL;DR: In this paper, the effect of lateral methoxy and polar hydroxy groups on the mesomorphism of Schiff's base esters was studied, based on thermal properties and textural analysis, which indicated that compounds with the larger number of carbons in the alkyl chain prefer smectic phase formation and possess higher transition temperatures and molecular polarizability along the long axis.
Abstract: Three series of Schiff's base esters, 2‐hydroxy‐4‐methoxybenzylidene‐4′‐alkanoyloxyaniline, 2‐hydroxy‐3‐methoxybenzylidene‐4′‐alkanoyloxyaniline and 3‐methoxy‐4‐alkanoyloxybenzylidene‐4′‐alkanoyloxyaniline, which possess mono‐ and di‐substituted moieties at both ends of the molecules have been synthesized and their mesomorphic properties investigated along with physical characterization (elemental analysis, mass spectrometry, Fourier transform IR and high resolution NMR). The effect of lateral methoxy and polar hydroxy groups on the mesomorphism of the title compounds was studied, based on the thermal properties and textural analysis. The results indicate that compounds with the larger number of carbons in the alkyl chain prefer smectic phase formation and possess higher transition temperatures and molecular polarizability along the long axis. Further analysis shows that the greater shielding effect (through the formation of intramolecular interaction) leads to lower molecular broadening and results in hi...
78 citations
TL;DR: A Commentary on the paper ''The synthesis of triphenylene-based discotic mesogens'' by N. Boden, R. C. Borner and M. V. Jesudason is given in this article.
Abstract: A Commentary on the paper ''The synthesis of triphenylene-based discotic mesogens. New and improved routes'', by N. Boden, R. C. Borner, R. J. Bushby, A. N. Cammidge and M. V. Jesudason. First published in Liquid Crystals, 15, 851-858 (1993).
72 citations
TL;DR: In this paper, a new approach for estimating the Leslie coefficients of liquid crystals based on MBBA data is presented, where literature values of the temperature-dependent Leslie viscosity coefficients of MBBA are used to fit with the analytical functions of Leslie coefficients based on the Imura and Okano theory, and a set of constants in these functions are determined.
Abstract: A new effective approach for estimating the Leslie coefficients of liquid crystals based on MBBA data is presented. Literature values of the temperature‐dependent Leslie viscosity coefficients of MBBA are used to fit with the analytical functions of Leslie coefficients based on the Imura and Okano theory, and a set of constants in these functions are determined. The same functions are then applied to two high birefringence liquid crystal mixtures, E7 and UCF‐2, to extract their Leslie coefficients based on their order parameters. Using the extracted Leslie coefficients, the simulation results agree very well with the experimental data.
63 citations
TL;DR: In this article, an electro-optical technique was used to measure the rotational viscosity of nematic liquid crystals, whose structures were chosen to investigate the effects of linking groups and lateral groups on rotational viscosity.
Abstract: An electro‐optical technique was used to measure the rotational viscosity of nematic liquid crystals, whose structures were chosen to investigate the effects of linking groups and lateral groups on rotational viscosity. These results are compared with the theory developed by Osipov and Terentjev. It is shown that the theory is useful in predicting rotational viscosity for specific molecular structures. The agreement between theory and experiment is found to be good for all the liquid crystals studied.
58 citations
TL;DR: The synthesis and liquid crystalline properties of new series of 1,2,4 and 1,3,4oxadiazole derivatives (2a−f and 5a-f respectively) are reported in this article.
Abstract: The synthesis and liquid crystalline properties of new series of 1,2,4‐ and 1,3,4‐oxadiazole derivatives (2a–f and 5a–f respectively) are reported. These compounds contain only one terminal flexible alkoxy chain, the other terminal substituent is a protecting benzyl group. All compounds of series 2 exhibit an enantiotropic nematic phase. The homologue with the longest chain (2f) displays an enantiotropic dimorphism smectic A– nematic. None of the compounds of series 5 shows mesomorphism and only crystal–isotropic transitions were observed. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X‐ray measurements. Luminescence properties, in chloroform solution, of 2f and the series 5 compounds were evaluated. Good photoluminescence quantum yields for compounds of series 5 were observed. Compound 2f, incorporating the 1,2,4‐oxadiazole ring shows a very strong reduction in emissive properties.
52 citations
TL;DR: Drzaic et al. as discussed by the authors provided a commentary on the paper "Reorientation dynamics of polymer dispersed nematic liquid crystal films" by P. Drzaic, which was published in Liquid Crystals, 3, 1543-1559 (1988).
Abstract: A Commentary on the paper ”Reorientation dynamics of polymer dispersed nematic liquid crystal films„, by P. Drzaic. First published in Liquid Crystals, 3, 1543‐1559 (1988).
49 citations
TL;DR: Several difluoroisothiocyanato-based biphenyl tolanes exhibiting high optical birefringence are presented and their representative molecular structure is shown below as mentioned in this paper.
Abstract: Several difluoroisothiocyanato‐based biphenyl tolanes exhibiting high optical birefringence are presented and their representative molecular structure is shown below. The optical birefringence of these liquid crystals lies between 0.44 to 0.48. Several eutectic mixtures of the biphenyltolanes with other compounds have been formulated and their properties investigated. The molecular simulations of polarizability and dipole moment of biphenyl tolanes are also presented.
43 citations
TL;DR: In this paper, the authors have designed novel liquid crystal oligomers in which three mesogenic units are connected via 3,5-dihydroxybenzoic acid, and their physical properties investigated by optical microscopy and differential scanning calorimetry.
Abstract: We have designed novel liquid crystal oligomers in which three mesogenic units are connected via 3,5‐dihydroxybenzoic acid. 4‐Cyanobiphenyl‐4′‐yl 3,5‐bis{6‐[4‐(5‐octylpyrimidin‐2‐yl)phenyloxy]hexyloxy}benzoate and 4‐(5‐octylpyrimidine‐2‐yl)phenyl 3,5‐bis{6‐[4‐(5‐octylpyrimidine‐2‐yl)phenyloxy]hexyloxy}benzoate have been prepared, and their physical properties investigated by optical microscopy and differential scanning calorimetry. The Y‐shaped liquid crystal oligomers were found to show a direct phase transition from isotropic liquid to anticlinic SmC (SmCanti) phase.
TL;DR: In this article, a click reaction based 1,2,3 triazole synthesis was successfully applied in the preparation of two series of nonlinear mesogens, based on 1,4−diaryl−[1, 2,3]−triazole (Ia−e) and with Schiff's base units (IIa−c).
Abstract: Regioselective synthesis of [1,2,3]‐triazoles based on the ‘click‐reaction’, involving the Cu(I)‐catalysed 1,3‐dipolar cycloaddition of aryl azide to terminal arylacetylenes, was successfully employed in the preparation of two series of non‐linear mesogens, based on 1,4‐diaryl‐[1,2,3]‐triazole (Ia–e) and with Schiff's base units (IIa–c). Their mesophases were characterized by polarizing optical microscopy and differential scanning calorimetry. All final compounds exhibited preferentially the SmC phase. In addition, compounds of series I showed weak blue fluorescence in solution (λmax. em. = 380–386 nm) with poor quantum yields and a Stokes shift of around 90 nm.
TL;DR: In this paper, it has been shown that the structure of the liquid crystal molecules in the Langmuir films is correlated with their ability to form corresponding mesophase in the bulk.
Abstract: Langmuir films of members of two homologous series, the 4‐n‐alkyl‐4′‐cyanobiphenyls (nCB) for n = 2–14 and trans‐4‐n‐alkyl(4′‐cyanophenyl)cyclohexanes (PCHn) for n = 2–12, have been studied by recording surface pressure/area isotherms and by Brewster angle microscopy. It has been found that the compounds with very short chains (n3) and very long chains (n>12 for nCB, n>10 for PCHn) are unable to form compressible monolayers at the air–water interface. Other members of both series can form stable Langmuir films, but both their rigidity and stability as well as the molecular packing vary with the alkyl chain length. The isotherms and BAM images imply that the organization of the liquid crystal molecules in the films is to some extent correlated with their ability to form corresponding mesophase in the bulk: nematogenic compounds tend to form rounded droplet‐like domains, whereas smectogenic compounds tend to form flat domains.
TL;DR: In this paper, a bent-shaped mesogens based on substituted naphthalene 2,7-diol, possessing a double bond at the end of terminal branches, have been synthesized and characterized.
Abstract: Novel bent‐shaped mesogens based on substituted naphthalene‐2,7‐diol, possessing a double bond at the end of terminal branches, have been synthesized and characterized. A variety of banana‐mesophases has been found, depending on the type of lateral substitution. Increasing the length of the alkyl chain leads to the appearance of the SmCAPA phase for two of the compounds synthesized. Under an electric field a transition into the SmCSPF phase takes place and a tilt angle close to 45° has been found. These materials are appropriate for the preparation of polymeric materials.
TL;DR: In this paper, two new chiral liquid crystalline monomers with bilactate or trilactate chiral units were synthesized and studied, and the monomers show the paraelectric SmA and ferroelectric SmC∗ phases.
Abstract: Two new chiral liquid crystalline monomers with bilactate or trilactate chiral units were synthesized and studied. The monomers show the paraelectric SmA and ferroelectric SmC∗ phases. The antiferroelectric phase was detected only for the monomer possessing the bilactate unit. The temperature dependences of the spontaneous polarization and spontaneous tilt angle were measured. Real and imaginary parts of the complex permittivity were studied as a function of frequency and temperature. The synthesized monomers contain a double bond at the end of the achiral terminal chain, and were used to prepare liquid crystalline polysiloxanes.
TL;DR: Pfannemuller et al. as mentioned in this paper described the liquid crystal behavior in the nalkyl gluconamides and other related carbohydrates and provided a commentary on the paper.
Abstract: A Commentary on the paper ”Liquid‐crystalline behaviour in the n‐alkyl gluconamides and other related carbohydrates„, by B. Pfannemuller, W. Welte, E. Chin and J.W. Goodby. First published in Liquid Crystals, 1, 357‐370 (1986).
TL;DR: In this article, the effect of photoisomerization of E-Z structures on the optical behavior of cholesteric liquid crystal (ChLC) cells was investigated, and a series of novel azo derivatives was synthesized.
Abstract: In order to investigate the effect of photoisomerization of E–Z structures on the optical behaviour of cholesteric liquid crystal (ChLC) cells, a series of novel azo derivatives was synthesized. Molecular structures were identified using 1H NMR, 13C NMR, FTIR and elemental analysis. Thermal properties and the specific rotation of the synthesized chiral azo derivatives were estimated. Rubbed polyvinyl alcohol coated on the inner surface of substrates was used to control the liquid crystal alignment in cells. The effect of chiral dopants on the reflection band of ChLC cells was investigated, as well as the dependence of polarizing optical microscope textures on temperature. The stability and reproducibility of the effect of UV irradiation on the cell reflection band and real image recording were confirmed. Real image recording of the ChLC cells fabricated in this investigation was also studied; a photoinduced image through a mask is given. Photoirradiated and non‐irradiated areas appear as different reflect...
TL;DR: In this paper, a phenomenological model of a gliding of easy axes is proposed to explain the slow surface reorientation and memory effects of a nematic liquid crystal on solid substrates.
Abstract: We present new results of experimental investigations of azimuthal director reorientation dynamics for a nematic liquid crystal on solid substrates. Two types of substrate with weak anchoring were studied: glass/polystyrene and glass/UV‐activated dye. Slow and fast relaxation processes were observed in both cases under the action of a strong ‘in‐plane’ electric field. The slow surface reorientation and memory effects were controlled by two parameters: the electric voltage and the excitation time. It was established that the increase of the excitation time results in a slowing of the relaxation of the system to the initial state after turning off the electric field. A phenomenological model of a gliding of easy axes is proposed to explain the slow relaxation process.
TL;DR: In this paper, a numerical fitting algorithm based on the Berreman 4×4 matrix technique was used to obtain high resolution reflection spectra for the chiral nematic liquid crystals and provided accurate information on changes in the pitch, refractive indices, device thickness and change in the surface director.
Abstract: The phenomenon whereby sudden changes in helicoidal pitch occur in thin chiral nematic devices with strong surface anchoring has been studied experimentally. This has been done with the aim of examining the underlying process in the context of existing theory. Thin devices (∼2.5 µm thick) containing two commercially available chiral nematic liquid crystals were employed in the study. The samples were chosen for their dependence of pitch on temperature; one exhibits a very slow increase in pitch with increasing temperature (95.6% of the Merck material BL131 in BL130), while the second shows the more common rapid reduction in pitch with increasing temperature (the Merck mixture TM1001). High resolution reflection spectra were obtained for the devices and a numerical fitting algorithm, based on the Berreman 4×4 matrix technique, provided accurate information on changes in the pitch, refractive indices, device thickness and changes in the surface director across the pitch jump region. We demonstrate that chan...
TL;DR: In this paper, high birefringence and low viscosity isothiocyanate liquid crystal single compounds, and eutectic mixtures based solely on unsaturated rigid core structures, are reported.
Abstract: High birefringence and low viscosity isothiocyanate liquid crystal single compounds, and eutectic mixtures based solely on unsaturated rigid core structures, are reported. Extraordinarily high values of figure‐of‐merit were observed at room temperature for the formulated nematic mixtures. Potential applications of such mixtures for laser beam steering at λ = 1.55 µm using optical phased arrays are emphasized.
TL;DR: In this paper, a polymer nematic nanocomposites containing 1.43-4.64% of silver nanoparticles whose mean dimensions are 2-4nm were presented.
Abstract: New polymer nematic nanocomposites are prepared containing 1.43–4.64 wt % of silver nanoparticles whose mean dimensions are 2–4 nm. According to 2H NMR spectroscopic measurements, on increasing the content of metallic nanoparticles, the orientational order parameter Szz of the nematic phase shown by the nanocomposites increases.
TL;DR: The mesomorphic properties of porphyrin derivatives with twelve flexible alkyl chains were investigated by DSC, WAXD and polarizing optical microscopy as mentioned in this paper, and the results showed that 1a and 2a exhibit a pseudo-hexagonal columnar phase, and 1b a rectangular (Col) phase over a wide temperature range including room temperature.
Abstract: Novel porphyrin derivatives with twelve flexible alkyl chains, namely meso‐tetra[4‐(3,4,5‐n‐trialkoxybenzoylamino)phenyl]porphyrins (1a, n = 12; 1b, n = 16) and the zinc complex (2a) were synthesized The mesomorphic properties were investigated by DSC, WAXD and polarizing optical microscopy; the results showed that 1a and 2a exhibit a pseudo‐hexagonal columnar phase, and 1b a rectangular (Col) phase over a wide temperature range including room temperature
TL;DR: In this paper, the authors demonstrate the ability to tune the physical properties of a liquid crystal elastomer (LCE) by varying the amount and type of crosslinking within the elastic network.
Abstract: In this report we demonstrate the ability to tune the physical properties of a liquid crystal elastomer (LCE) by varying the amount and type of crosslinking within the elastomer network. LCE films composed of a single mesogenic compound were capable of uniaxial contraction when thermally actuated through the nematic to isotropic phase of the material. We probed the physical properties of the LCE films while varying the amount and concentration of two crosslinking agents and measured actuation strains of 10–35%, elastic moduli of 3–14 MPa, and transition temperatures ranging between 75 and 60°C. The viscous losses of the elastomers and the estimated work capable of being produced by the films were also evaluated. The ability to tune the physical properties of the LCE films allows for a wide range of applications including robotics, microelectromechanical systems (MEMS), shape‐changing membranes, and/or microfluidics.
TL;DR: In this paper, eight banana-shaped side chain liquid crystalline oligomers and polymers were synthesized by hydrosilylation of vinyl-terminated bent-core mesogens with trimethylsilyl−terminated siloxanes, and they were investigated by polarizing optical microscopy (POM), differential scanning calorimetry, X-ray diffraction (XRD), electro-optical experiments and Maldi-Tof.
Abstract: Eight banana‐shaped side chain liquid crystalline oligomers and polymers have been synthesized by hydrosilylation of vinyl‐terminated bent‐core mesogens with trimethylsilyl‐terminated siloxanes. The synthesized oligomers and polymers, and their olefinic precursors, were investigated by polarizing optical microscopy (POM), differential scanning calorimetry, X‐ray diffraction (XRD), electro‐optical experiments and Maldi‐Tof. The short‐tailed olefins form a Colr mesophase, whereas those with longer chains exhibit the SmCPA mesophase. All the oligomers and polymers studied show liquid crystalline properties and do not crystallize upon cooling. Most oligomers with around four repeating siloxane units, show a lamellar (layer) structure and antiferroelectric switching properties, the SmCPA phase. XRD shows that the layer spacings are hardly influenced by the length of the terminal tails. The oligomer prepared from the smallest olefinic precursor, having the shortest alkyl tail, shows an XRD pattern reminiscent o...
TL;DR: In this article, liquid crystalline esters with a perfluorocarbonyloxy terminal chain and lateral fluoro substituents were synthesized to determine their influence on mesomorphic behavior, tilt angle and spontaneous polarization.
Abstract: Novel liquid crystalline esters have been synthesized with a perfluorocarbonyloxy terminal chain and lateral fluoro substituents in order to determine their influence on mesomorphic behaviour, tilt angle and spontaneous polarization. Certain locations of lateral fluoro substituents provide for very low melting points and reasonably wide temperature ranges of the antiferroelectric phase, and can generate enhanced tilt angles of up to 45°, although spontaneous polarization is always lower than for the parent system without lateral fluoro substituents. Thus, these novel materials, particularly as components in mixtures, should be useful in high tilt antiferroelectric (orthoconic) applications.
TL;DR: Wu et al. as discussed by the authors provided a commentary on the paper "Response times and voltages for PDLC shutters" by Bao-Gang Wu, John H. Erdman and J. William Doane.
Abstract: A Commentary on the paper ”Response times and voltages for PDLC shutters„, by Bao‐Gang Wu, John H. Erdman and J. William Doane. First published in Liquid Crystals, 5, 1453‐1465 (1989).
TL;DR: In this paper, the degree of colour shift depending on viewing direction in the inplane switching (IPS) mode has been investigated and it was shown that the IPS cell with pure twist deformation exhibits a stronger colour shift than the one with tilt and twist deformations, although the former has better luminance uniformity in the bright state than the latter.
Abstract: The degree of colour shift depending on viewing direction in the in‐plane switching (IPS) mode has been investigated. The IPS cell with pure twist deformation exhibits a stronger colour shift than that of the IPS cell with tilt as well as twist deformation, although the former has better luminance uniformity in the bright state than the latter. Furthermore, the IPS cell with multi‐directional LC orientation, with tilt as well as twist deformation, shows the least colour shift.
TL;DR: In this paper, the synthesis of new liquid crystalline 3-aryl−5−alkylisoxazoles, 3−aryl−1H−pyrazoles with ether or ester bridges are reported.
Abstract: The syntheses of new liquid crystalline 3‐aryl‐5‐alkylisoxazoles, 3‐aryl‐5‐alkyl‐1H‐pyrazoles and 3‐aryl‐5‐alkyl‐2‐isoxazolines with ether or ester bridges are reported. The key stage in the synthesis is the oxidation of the 2‐isoxazoline ring to isoxazole. The influences of core‐heterocycle type and bridging group on the mesomorphic properties for the prepared compounds are discussed.
TL;DR: In this paper, two series of UV-curable rod-like diacrylates containing bis-tolane (M1−M5) and bis-stilbene (M6−M10) mesogens were synthesized.
Abstract: Two series of UV‐curable rod‐like diacrylates containing bis‐tolane (M1–M5) and bis‐stilbene (M6–M10) mesogens were synthesized. All of the diacrylates were prepared through convergent syntheses involving palladium‐catalysed coupling reactions. The thermal transitions and mesomorphic properties of the diacrylates were characterized by differential scanning calorimetry and optical microscopy. All the bis‐tolane‐based monomers reveal nematic phases, except M5 which shows no mesomorphic behaviour. For the bis‐stilbene based monomers, most show no mesomorphic behavior and only M7 and M9 exhibit a SmA phase.
TL;DR: In this article, the universal growth law was used to model the nucleus growth during a quench across the isotropic to nematic phase transition for a siloxane-azomethine polyether at cooling rates of 10 and 20°Cmin−1.
Abstract: Kinetics of the nucleus growth during a deep temperature quench across the isotropic to nematic phase transition was experimentally investigated for a siloxane‐azomethine polyether at cooling rates of 10 and 20°C min−1. Nematic droplets revealed in the optical images during the phase separation were treated statistically and the resulting statistical size distributions were described using the model of reversible aggregation. Analysis of the time‐dependent distribution parameters allowed two processes involved in liquid crystal phase ordering to be identified: nucleus growth and nucleus coarsening. Both regimes are quantitatively described using the universal growth law.