Showing papers in "Molecular Crystals and Liquid Crystals in 2015"
TL;DR: In this paper, the authors focus on various issues surrounding the mathematical description of defects in models of liquid crystals, drawing on experience from solid mechanics, and highlight the roles played by a suitable choice of function space and by the growth properties of the free-energy density.
Abstract: The paper is concerned with various issues surrounding the mathematical description of defects in models of liquid crystals, drawing on experience from solid mechanics. The roles played by a suitable choice of function space and by the growth properties of the free-energy density are highlighted. Models in which the director can jump across surfaces are formulated, and their relevance for nematic elastomers, order reconstruction and smectic A thin films discussed.
29 citations
TL;DR: In this article, a model of the LC alignment in a porous system is proposed and the LC orientation type is determined by the free anchoring energy and the micropore diameter.
Abstract: A porous system for LC alignment is reviewed. Fabrication of nanomesh aluminum films and their porous structure are described. Methods of the nanomesh parameters for optimal LC alignment are discussed. A model of the LC alignment in a porous system is proposed. The LC orientation type is determined by the free anchoring energy and the micropore diameter. The difference between planar and homeotropic anchoring energies appears to be lower than the interaction energy by two orders of magnitude.
25 citations
TL;DR: In this paper, a novel organic nonlinear optical (NLO) compound (2E)-3-(2-methylphenyl)-1-(4-nitrophenyl) prop-2-en-1-one (2MPNP) has been synthesized and grown as a high-quality single crystal by the slow evaporation technique.
Abstract: A novel organic nonlinear optical (NLO) compound (2E)-3-(2-methylphenyl)-1-(4-nitrophenyl) prop-2-en-1-one (2MPNP) has been synthesized and grown as a high-quality single crystal by the slow evaporation technique. 2MPNP crystals were characterized by FT-IR, UV-Vis-NIR, NMR, DSC, and Single Crystal XRD techniques. 2MPNP crystallizes in the orthorhombic crystal class in the noncentrosymmetric space group Pca21 with cell parameters a = 29.905(4) A, b = 4.8241(5) A, c = 9.0984(10) A, α = β = γ = 90.00°, and V = 1312.58 A3 and Z = 4. Second harmonic generation (SHG) efficiency of the grown crystal was found to be 1.17 times that of urea. Thermal analysis reveals that the crystal has better thermal stability.
23 citations
TL;DR: In this article, a simple method to enhance the conductivity of poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) thin films from 0.7 to 1185 S/cm by post-treatment with dimethyl sulfoxide (DMSO) is demonstrated.
Abstract: In this study, a simple method to enhance the conductivity of poly(3,4-ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) thin films from 0.7 to 1185 S/cm by post-treatment with dimethyl sulfoxide (DMSO) is demonstrated. After the rubbing technique was applied, the DMSO-treated PEDOT:PSS film was used as both transparent electrode and alignment layer to fabricate ITO-free liquid crystal (LC) cells. The electro-optical properties of LC cells fabricated by rubbed PEDOT:PSS were compared to those constructed by ITO and polyimide. This work indicates that highly conductive PEDOT:PSS film is a promising material for ITO-free LC devices.
22 citations
TL;DR: Rod-like gold(I) complexes with phenyl, biphenyl, or naphthyl rings in a mesogenic core were synthesized by complexation of ethynyl-substituted aromatic derivatives with (tetrahydrothiophene)AuCl, followed by ligand exchange with alkyl isocyanide, to investigate the effects of molecular and molecular-aggregated structures on their liquid-crystalline (LC) behavior and photoluminescence properties.
Abstract: Rod-like gold(I) complexes with phenyl, biphenyl, or naphthyl rings in a mesogenic core were synthesized by complexation of ethynyl-substituted aromatic derivatives with (tetrahydrothiophene)AuCl, followed by ligand exchange with alkyl isocyanide, to investigate the effects of molecular and molecular-aggregated structures on their liquid-crystalline (LC) behavior and photoluminescence properties. The gold complexes exhibited enantiotropic liquid crystallinity. Introduction of multi-ring systems into the mesogenic core effectively expanded the LC temperature range. A comparison of the photoluminescence properties in the crystalline phase showed that the molecular-aggregated structure plays a crucial role in the luminescence of these gold complexes.
21 citations
TL;DR: In this article, a novel homologous series consists of 11 homologues, studied with a view to understand and establish the relations between mesomorphism and molecular structure of novel substances.
Abstract: A novel homologous series consists of 11 homologues, studied with a view to understand and establish the relations between mesomorphism and molecular structure of novel substances. All the novel members of a series except methoxy and pentyloxy homologue derivatives are liquid crystalline [LC] in nature. Mesomorphism commences from a second member of a series ethoxy, propyloxy, butyloxy, and hexyloxy to hexadecyloxy homologue derivatives are nematogenic while decyloxy, dodecyloxy, and tetradecyloxy homologue derivatives are smectogenic, in addition to nematogenic. All mesogenic homologues of a series are enantiotropic mesomorphic. Phase transition curve for Smectic-Nematic behave in normal manner without exhibition of odd-even effect, whereas nematic-isotropic transition curve adopts serpentile shape as rising and falling nature with exhibition of very minor odd-even effect. Textures of nematic phase are threaded or schlieren and that of a smectic mesophase is a focal conic fan shaped of the type smectic A...
20 citations
TL;DR: In this paper, the effects of the laser fluence on the characteristics of ZnO nanoparticles produced by pulsed laser ablation of a Zn plate in acetone were studied.
Abstract: We have studied the effects of the laser fluence on the characteristics of ZnO nanoparticles produced by pulsed laser ablation (PLA) of Zn plate in acetone. The beam of a Q-switched Nd:YAG laser of 1064 wavelength at 7 ns pulse width and different fluencies was employed to produce nanoparticles. The ZnO nanoparticles were found to be hexagonal. The size distribution of generated nanoparticles is increased by increasing the laser fluence. The production rate of nanoparticles is increased with increasing the laser fluence. ZnO nanoparticles were formed with spherical shape. The bandgap energy of nanoparticles is calculated to be 3.59–3.89 eV. In this range of ZnO nanoparticle size, photoluminescence spectrum exhibits two peaks due to bandgap transition and defect levels.
20 citations
TL;DR: In this paper, the authors demonstrate high-performance photo-actuation of nematic liquid crystal elastomer (LCE) nanocomposites incorporating graphene oxide (GO), which absorbs photons and converts the photonic energy to heat.
Abstract: The authors demonstrate high-performance photo-actuation of nematic liquid crystal elastomer (LCE) nanocomposites incorporating graphene oxide (GO). The nematic LCE serves as the matrix with reversible thermomechanical response. The incorporated GO absorbs photons and converts the photonic energy to heat, thus actuating the LCE nanocomposite. Both infrared and visible lights of wide spectrum (white light) or various wavelength ranges irradiations are able to effectively actuate the LCE nanocomposites, thus proves that they can fully utilize the photo energy of a light source for their mechanical actuation. Attributed to the well dispersity of GO in LCE matrix, sensitive (in seconds) and reversible photo-induced strain of LCE nanocomposites with consistent shape-changing ratio and significantly enhanced mechanical properties are observed. The contraction of the LCE nanocomposite films under light irradiation is about one third of the original length. The effective load-actuation capability is elevated abou...
19 citations
TL;DR: In this article, the discovery of micrometre-scale periodic patterns at the N-Ntb phase transition interface and sub-micrometer scale patterns in the Ntb phases were reported.
Abstract: Several attractive properties of hydrocarbon-linked mesogenic dimers have been discovered, a major feature of these has been the ability of dimers under confinement to form periodic patterns. At least six different types of stripe-like periodic patterns can be observed in these materials under various experimental conditions. Our most recent finding is the discovery of micrometre-scale periodic patterns at the N-Ntb phase transition interface, and sub-micrometre scale patterns in the Ntb phase. Layer-like sub-micrometre patterns were observed using three-photon excitation fluorescence polarizing microscopy, and these are being reported here.
19 citations
TL;DR: For interaction energy of mesogenic model rod-like molecules an analytical expression was obtained in this article, where it was shown that dipole moments interaction is much less than the total interaction energy.
Abstract: For interaction energy of mesogenic model rod-like molecules an analytical expression is obtained. Interaction energy of dipole moments interaction is much less than the total interaction energy. T...
18 citations
TL;DR: In this paper, a series of cholesterol-based liquid crystalline (LC) dimers with a menthyl terminal group in the biphenyl base side have been synthesized.
Abstract: A novel series of cholesterol-based liquid crystalline (LC) dimers with a menthyl terminal group in the biphenyl base side have been synthesized. The chemical structures and LC properties of this series of compounds are characterized by FT-IR, 1H-NMR, elemental analysis, hot-stage coupled polarizing microscopy and differential scanning calorimetry. All the dimers exhibit enantiotropic mesophases. These dimesogenic compounds with a short spacer are chiral nematic LCs, while with long spacers, they are SmA and chiral nematic LCs. Some of these LC dimers exhibit iridescent colors in their chial nematic (N*) states.
TL;DR: A facile chemical synthesis of poly(methyl methacrylate) (PMMA) grafted CdTe nanocrystals (CdTe NCs) has been realized as mentioned in this paper.
Abstract: A facile chemical synthesis of poly(methyl methacrylate) (PMMA) grafted CdTe nanocrystals (CdTe NCs) has been realized. Initially, CdTe NCs were prepared in a controlled manner using 2-mercaptoehanol (ME) as a capping agent. Then, 3-(trimethoxysilyl) propyl methacrylate having C˭C double bonds were anchored with ME capped CdTe NCs through condensation reaction. Subsequently, AIBN initiated in situ free radical polymerization provided PMMA-g-CdTe nanohybrids. The FT-IR investigation suggested the formation of robust covalent bonding between CdTe NCs and the organic PMMA segment. XPS analysis also confirmed PMMA-g-CdTe nanohybrids. The physical structure and morphology of the as-prepared nanohybrids were studied by XRD and TEM. The thermal stability of the hybrids was enhanced in comparison with pure PMMA as indicated by TGA analysis. The UV-Vis absorption and photoluminescence measurements of the PMMA-g-CdTe nanohybrids showed their potential optical properties.
TL;DR: In this paper, the authors deal with the studies on synthesis, characterization, nonlinear absorption, and optical-limiting property of a new organic crystal 3-(3-fluorophenyl)-1-[4-(methylsulfanyl) phenyl] prop-2-en-1-one (FMP).
Abstract: This paper deals with the studies on synthesis, characterization, nonlinear absorption, and optical-limiting property of a new organic crystal 3-(3-fluorophenyl)-1-[4-(methylsulfanyl) phenyl] prop-2-en-1-one (FMP). Primary characterization of FMP samples were performed using FTIR, UV-Visible, and NMR Spectroscopy techniques. FMP crystallizes in monoclinic system with centrosymmetric space group P21/n. UV-Visible spectrum shows minimum absorption in the entire visible region. From the thermo gravimetric and differential scanning calorimetry, melting point of FMP was found to be 96°C and there was no phase transition below this temperature. Open aperture Z scan experiment of FMP showed a good nonlinear absorption and optical-limiting property.
TL;DR: In this paper, a novel homologous series of liquid crystalline 4-(4′-n-alkoxy cinnamoyloxy)-4″-methoxy benzyl Cinnamates was synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal behavior.
Abstract: A novel homologous series of liquid crystalline 4-(4′-n-alkoxy cinnamoyloxy)-4″-methoxy benzyl cinnamates was synthesized and studied with a view to understand and establish the effects of molecular structure on liquid crystal behavior. The series consists of eleven members of the series. None of the homologue derivatives are either nonliquid crystal or smectogenic, i.e. all the eleven members of the novel homologous series are enantiotropcially nematogenic only. Transition and melting temperatures as well as textures of the nematic mesophase were determined on an optical polarizing microscope equipped with a heating stage. The transition curves of the phase diagram show phase behavior in a normal expected manner. An odd-even effect is observed for the nematic-isotropic transition curve. The textures of the nematic mesophase are threaded or Schlieren as determined a by miscibility method. Analytical and spectral data confirm the molecular structures of the homologues. The average thermal stability for nem...
TL;DR: In this article, a phase shifter for W-band frequencies has been fabricated, which reached a measured figure of merit for passive phase shifters of up to 148° /dB, based on a specialized liquid crystal simulation tool, different tuneable waveguide topologies are compared in terms of tuneability, transmission loss and tuning speed.
Abstract: This work represents the evolution of micro- and millimetre wave optimized nematic liquid crystal mixtures and their applications. Starting with the well-known liquid crystal mixture K15 used in the display technology, microwave optimized LC mixtures have been developed. For that, novel characterization setups have been developed, which play an essential factor in the optimization process for the micro-, millimetre wave and THz regime. By using a specialized LC simulation tool, different tuneable waveguide topologies are compared in terms of tuneability, transmission loss and tuning speed. Based on that, a phase shifter for W-band frequencies has been fabricated, which reached a measured figure of merit for passive phase shifters of up to 148° /dB.
TL;DR: In this paper, liquid crystal elastomers (LCEs) are used for actuator materials and they are shown to be a good actuator material, however, current LCE materials are generally made in the forms with thin thickness, such as films or fibers, which have limitation.
Abstract: Liquid crystal elastomers (LCEs) are excellent actuator materials. However, current LCE materials are generally made in the forms with thin thickness, such as films or fibers, which have limitation...
TL;DR: In this paper, a plasmonic strain sensor based on gold nanoparticles deposited onto elastomeric films is presented, which demonstrates how the combined effect of nanoparticle growth and stretching influences the average normalized gap between particles, thus modifying the extinction spectra of the sample.
Abstract: We have carried out an experiment on a flexible polymeric substrate, coated with a monolayer of gold nanoparticles, which demonstrates how the combined effect of nanoparticle growth and stretching influences the average normalized gap between particles, thus modifying the extinction spectra of the sample. The study paves the way for the realization of a plasmonic strain sensor based on the plasmonic coupling of gold nanoparticles deposited onto elastomeric films: application of a mechanical stretching induces a change of colour of the device and a fine control of the applied strain allows a continuous tuning of the colour.
TL;DR: In this article, the isothermal crystallization kinetics of 4n-pentyl-4-cyanobiphenyl (5CB) was studied with Differential Scanning Calorimetry (DSC) and Dielectric Relaxation Spectroscopy (DRS).
Abstract: The isothermal crystallization kinetics of 4-n-pentyl-4–cyanobiphenyl (5CB) has been studied with Differential Scanning Calorimetry (DSC) and Dielectric Relaxation Spectroscopy (DRS). 5CB is a well characterized material which makes it ideal for a dielectric and thermal comparative study. The effect that isothermal crystallization exerts on the behavior of relaxation processes α and δ by cooling the isotropic liquid below the nematic phase or through the process of cold crystallization by heating it from the supercooled state is explored by comparing the DRS and DSC. Furthermore, by employing the Avrami equation, we compare the ability to probe the crystallization with each technique.
TL;DR: In this article, a combination of characteristics of short pitch liquid crystalline compounds and noble metal nanoparticles (MNPs) has demonstrated effective to provide an advanced tool to monitor nanoscale temperature variations.
Abstract: Localized plasmon resonance (LPR) of noble Metal Nanoparticles (MNPs) opens up a new horizon for nanoscale materials able to convert light into heat, since the strong electric field generated around the MNPs can transform them into original heat nanosources. Thus, investigation of the heat transport mechanism, from the heated MNPs to their surrounding medium, is fundamental for realizing applications in nanotechnology and thermal-based therapies, and a challenge is definitely represented by the possibility of measuring temperature variations at the surface of the MNPs undergoing optical illumination. In this framework, we show that an ingenious combination of characteristics of short pitch liquid crystalline compounds and MNPs has demonstrated effective to provide an advanced tool to monitor nanoscale temperature variations.
TL;DR: In this paper, surface-functionalised laponite nanoplatelets dispersed in a chiral liquid crystal were shown to increase the temperature stability of blue phase I by a factor of two.
Abstract: We report on the widening of blue phase range induced by surface-functionalised laponite nanoplatelets dispersed in a chiral liquid crystal. The results are obtained by means of high-resolution ac calorimetry and optical microscopy and they are reproducible upon heating and cooling, identifying thermodynamically stable blue phases. It is shown that nanoplatelets target mostly the cubic structure of blue phase I and increase its temperature stability range by a factor of two. The present results are in agreement with recent findings that anisotropic nanoparticles tend to effectively stabilise blue phase I.
TL;DR: In this paper, the surface thiol-lactam-initiated radical polymerization (TLIRP) technique was used to synthesize poly(acrylic acid)/TiO2 (PAA-g-TiO 2) nanocomposites.
Abstract: Poly(acrylic acid)/TiO2 (PAA-g-TiO2) nanocomposites were synthesized by the surface thiol-lactam initiated radical polymerization (TLIRP) technique. The synthetic strategy involved the modification of TiO2by a one-step direct anchoring of thiol groups via reaction between the hydroxyl groups on the surface of TiO2 and triethoxysilane groups of (3-mercapto)propyltrimethoxysilane (MPTMS). The modified TiO2nanoparticles (NPs) were dispersed in acrylic acid monomers and subsequently polymerized by TLIRP to yield PAA-g-TiO2nanocomposites. FT-IR spectra, XPS, EDS, UV-Vis spectroscopy and SEM images provided direct and clear evidence for the coordination of MPTMS and the presence of PAA on TiO2 NPs. The immobilization of PAA onto TiO2 NPs significantly improved their dispersibility in organic solvents. Additionally, laser diffraction spectroscopy of the TiO2 NPs was examined in order to get the size distribution of nanocomposites.
TL;DR: In this paper, the diffusional properties of the ionic smectic phase formed by the cationic diffogen, N-docecyl-N'-methyl-imidazolium (C12mim), with two different counter ions are studied.
Abstract: Thermotropic ionic liquid crystals are considered very promising for a wide range of applications, such as anisotropic conductors as well as electrolytes in dye-synthesized solar cells Their potential comes from the unique combination of ionic conductivity and high polarizability In this paper we present a study of the diffusional properties of the ionic smectic A phase formed by the cationic smectogen, N-docecyl-N'-methyl-imidazolium (C12mim), with two different counter ions Experimental translational diffusion data measured by NMR diffusometry are collected both for cations and anions and discussed in terms of their different anisotropy
TL;DR: In this article, the average effective birefringence for the samples in a tube flow of aqueous GO dispersions with varying GO concentrations was quantitatively deduced the order parameter of GO particles.
Abstract: The flow-induced ordering of Graphene oxide (GO) particles was investigated in a tube flow of aqueous GO dispersions with varying GO concentrations. By measuring the average effective birefringence for the samples in a tube flow, we could quantitatively deduce the order parameter of GO particles. The flow-induced effective birefringence linearly increased as the GO concentration increased in isotropic phase, but the birefringence deviated from the linear tendency and increased more in biphase. We also calculated the S and P order parameters using the optical birefringence profile in the tube flow. The result showed that the S order parameter kept increasing as the GO concentration increased but the P order parameter decreased as the GO concentration increased. All these results indicate that the increase in inter-particle ordering interaction in biphase enhances the uniaxial S order parameter in the flow-induced ordering and suppresses the biased biaxial ordering.
TL;DR: This article designed crosslinked polysiloxane with side chain mesogens that contain exchangeable crosslinking points based on transesterification between phenyl benzoates and hydroxy groups.
Abstract: Crosslinked liquid-crystalline polymers (CLCPs) show unique behavior of deforming macroscopically when stimulated with heat, electricity and light However, they cannot be remolded and reshaped once prepared Here, we designed crosslinked polysiloxane with side chain mesogens that contain exchangeable crosslinking points based on transesterification between phenyl benzoates and hydroxy groups After the formation of a polymer network, a base catalyst was introduced into the CLCP When heated at 80°C, a piece of the CLCP was reshaped into a film and separate pieces of the CLCP were fused together, indicating that the CLCP is remoldable
TL;DR: Tristriazolotriazines with a threefold 3,5-dialkoxyphenyl substitution were prepared from the corresponding phenyltetrazoles and cyanuric chloride.
Abstract: Tristriazolotriazines with a threefold 3,5-dialkoxyphenyl substitution were prepared from the corresponding phenyltetrazoles and cyanuric chloride. These star-shaped compounds are discotic liquid crystals that form broad and stable thermotropic mesophases. The thermal behaviour was studied by DSC and polarizing optical microscopy. An increasing length of the side chains reduces the phase transition temperatures, this effect is more pronounced for the crystalline to mesophase transition than for the clearing temperature. XRD on an oriented sample revealed a hexagonal columnar structure for the mesophase. All TTTs emit a strong fluorescence in the UV-violet region.
TL;DR: In this article, a small series of partially alkylated bisindolylmaleimide dyes were prepared containing NO2 groups at the ortho, meta, and para position and the effect of substitution position in the aryl ring on the photophysical properties of the dyes was discussed in detail.
Abstract: A small series of partially alkylated bisindolylmaleimide dyes were prepared containing NO2 groups at the ortho, meta, and para position. The effect of substitution position in the aryl ring on the photophysical properties of the dyes is discussed in detail. The highly electron withdrawing NO2 makes different emission behavior of these dyes. Medium quantum yields of fluorescence in toluene solution are observed for derivative with NO2 substituted in the ortho position of aryl ring. Careful analysis of optimized structure and frontier molecular orbitals (HOMO/LUMO) suggests that the electronic rather than steric effect is controlling non-radiative decay.
TL;DR: In this paper, the authors presented detailed Monte Carlo simulations of a nematic cell with homeotropic boundary conditions at the four confining surfaces, based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the cell anchoring.
Abstract: We present detailed Monte Carlo (MC) simulations of a nematic cell with homeotropic boundary conditions at the four confining surfaces. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the cell anchoring. We have investigated the model using a standard Metropolis Monte Carlo method to study the optical transmission and the ordering through the cell.
TL;DR: Graphene/PANI nanocomposite multilayer CE was created through the insertion of a PANI layer in this article, which showed improved electrical conductivity, interface charge transfer rate and catalytic activity on I3− reduction compared with the Pt CE.
Abstract: Polyaniline (PANI) conducting polymer and graphene are preferred counter electrode (CE) materials for dye-sensitized solar cells (DSSC). Graphene/PANI nanocomposite multilayer CE is created through the insertion of a PANI layer. It has been demonstrated as a platinum-free counter electrode for cost-efficient DSSCs. Here, graphene/PANI nanocomposite and PANI were synthesized by electro-polymerization from a solution containing aniline monomers and graphene. Graphene/PANI nanocomposite multilayer CE showed improved electrical conductivity, interface charge transfer rate, and catalytic activity on I3− reduction compared with the Pt CE. The high electro-catalytic ability of graphene/PANI nanocomposite multilayer CE was demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy.
TL;DR: In the present study, the cytotoxicity of PNDs consisting of SN-38 dimer and podophyllotoxin dimer with size in the range 30–50 nm was evaluated in human cancer HepG2, KPL-4, and MCF-7 cells.
Abstract: Pure nanodrugs (PNDs) is a newly designed drug materials, which is a carrier-free drug nanoparticles fabricated by the reprecipitation method. In the present study, the cytotoxicity of PNDs consisting of SN-38 dimer and podophyllotoxin dimer with size in the range 30–50 nm was evaluated in human cancer HepG2, KPL-4, and MCF-7 cells. It was observed that the cytotoxicities of PNDs were changed depending on the type of cells. In addition, PNDs coated with polysorbate 80 showed higher activity than free PNDs, which suggests that the surface state of PNDs was the one of the important factors to affect cytotoxicity.
TL;DR: In this article, a liquid crystalline dendrimer having a cinnamate mesogen containing an azobenzene moiety (D-6AC2) was prepared as an alignment agent of nematic liquid crystals for a planar homogeneous alignment.
Abstract: A liquid crystalline dendrimer having a cinnamate mesogen containing an azobenzene moiety (D-6AC2) was prepared as an alignment agent of nematic liquid crystals for a planar homogeneous alignment. D-6AC2 is a thermotropic liquid crystal showing smectic phases. A mixture of ZLI-4792 with 1wt% of D-6AC2 exhibited a homeotropic alignment. After UV irradiation of the same sample, the schlieren texture due to a planar orientation was observed, and the texture was maintained even after 133 days. Thus D-6AC2 can induce the stable planar alignment of NLC upon UV irradiation. Furthermore, D-6AC2 could induce a planar homogeneous alignment by polarized UV light irradiation.