Showing papers in "Molecular Crystals and Liquid Crystals in 2007"

Biological Effects of C60 Fullerenes in vitro and in a Model System

Abstract: With the use of artificial lipid membranes, it is shown that C60 fullerenes are capable to penetrate into a lipid bilayer, by locally strengthening its conductivity. C60 fullerenes under the UV/VIS and X-ray irradiation do not influence the MTT reduction and the DNA structure in thymocytes. UV/VIS irradiated C60 fullerenes give rise to the DNA fragmentation and a decrease of the viability of ascitic Erlich carcinoma cells.

Ambipolar Charge Carrier Transport Properties in the Homologous Series of 2,3,6,7,10,11-hexaalkoxytriphenylene

Abstract: In this study, ambipolar charge carrier transport properties were investigated for a homologous series of triphenylene by time-of-flight (TOF) technique for the homeotropic domains. Ambipolar electronic charge carrier transport was observed and the both positive and negative charge carrier mobilities decrease with the increase of the alkyl chain length. Ionic conduction was also observed for the negative charge carrier transport except for C4OTP and any remarkable dependency of the alkyl chain length was not seen. It was reasonably found that both the positive and negative charged carrier mobilities by electronic hopping process is affected by the intra columnar order.

Optically Isotropic Chiral Liquid Crystals Induced by Polymer Network and Their Electro-Optical Behavior

Abstract: The optical and electro-optical properties of the optically isotropic liquid crystalline composites prepared by in-situ photo-polymerization of cross-linking monomers in the isotropic phase and the blue phase of the chiral liquid crystals were investigated. In the composites prepared in the isotropic phase, no typical platelet textures corresponding to blue phase I and blue phase II were seen, and no reflection peaks were observed around the wavelength where the polymer-stabilized blue phase should exhibit reflection. A large Kerr constant, being relatively insensitive to temperature, was obtained for composites even in a temperature range where a liquid crystal used exhibits chiral nematic phase. The response time of Kerr effect was on the order of tens to hundreds of microseconds.

Syntheses, structures, and mesomorphism of a series of Cu(II) salen complexes with 4-substituted long alkoxy chains

Abstract: A series of copper(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings [Cu((4-C n H2n+1O)2salen)] (n = 3 ( 1 ), 4 ( 2 ), 6 ( 3 ), 8 ( 4 ), 10 ( 5 ), 12 ( 6 ), 14 ( 7 ), 16 ( 8 ), 18 ( 9 ), and 20 ( 10 ) and salen (N,N'-ethylenebis(salicylideneiminato)) has been prepared, and single-crystal structures of 2 · H2O, 4 , and 6 by an X-ray crystallographic analysis have been revealed. Complexes 4 and 6 form tetrahedrally distorted square planer structure with one-dimensional polymeric stacking by van der Waals interaction between the dramatically distorted salen moieties. Complexes 1 – 3 did not exhibit any mesophases, but complexes 4 – 10 with longer alkoxy chains of n = 8–20 showed the metallomesogen of a lamello-columnar (ColL) mesophase in the smectic layers with the nearly constant stacking distances, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements, which show similar behaviors to the corresponding Ni(II) complexes of n = 14–20. The ...

Influence of Alkyl Chain Length on the Solid-State Packing and Fluorescence of 1,4,5,8-Tetra(alkyl)anthracenes

Abstract: 1,4,5,8-Tetra(alkyl)anthracenes (alkyl = methyl, ethyl, n-propyl, and n-hexyl) were prepared by a sequence of reactions of 1,2,4,5-tetrabromobenzene and 2,5-dialkylfurans in the presence of n-BuLi, hydrogenation, and treatment with acid. The influence of alkyl chain length on the packing patterns in the crystals and the fluorescent properties in the solid state was investigated. X-ray analysis revealed that the molecular structures can be classified into plane, semi-chair, and chair forms and that the packing patterns can be categorized into two-dimensional (herringbone) and one-dimensional (slipped-parallel) arrangements, in both of which there is no π–π stacking. In the case of the methyl, ethyl, and n-propyl derivatives, the wave shapes of the fluorescence spectra in the solid state resemble each other; on the other hand, the n-hexyl derivative displayed a slightly red-shifted and broader spectrum. The absolute quantum yield depended on the transition dipole moments because of the packing patterns and ...

Ellipsometric Study of Liquid Crystal Infiltrated Porous Silicon

Abstract: Porous silicon (PS) based devices are nowadays under an intense and widespread investigation in the optoelectronic and sensing fields. Recently, the range of possible applications has been widened ...

Polymethacryloylaminoarylmethacrylates: New Concept of Photoalignment Materials for Liquid Crystals

Abstract: New class of highly efficient polymers for liquid crystal (LC) photoalignment is proposed. These polymers are based on methacryloylaminoarylmethacrylates having two methacryloyl groups of different reactivity. The more active O-methacryloyl group is subjected to polymerization, while the less active NH-methacryloyl group undergoes photocrosslinking reaction in combination with Fries rearrangement. The latter process is anisotropic in case of polarized light irradiation that results in LC photoalignment with readily controlled pretilt angle and anchoring energy. The induced alignment shows high thermal and photo-stability.

Pet Fabric/Poly(3,4-Ethylenedioxythiophene) Composite with High Electrical Conductivity for EMI Shielding

Abstract: Highly electrically conducting fabrics were prepared by chemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on a PET fabric. Monomer solution was prepared by dissolving EDOT and poly(vinyl pyrrolidone) (PVP) as a binder in 1-butanol. The oxidant solution was prepared by dissolving ferric p-toluene sulfonate (FTS) in 1-butanol. The mixture of the monomer and oxidant solutions was applied to PET fabric and polymerization was carried out under various conditions. We studied the effect of the chemical polymerization conditions on the properties of resulting composites such as electrical conductivity and surface morphology, environmental stability, electromagnetic interference shielding effectiveness (EMI SE). The specific volume resistivity, specific surface resistivity and EMI SE of the resulting composite were extremely low as 0.15 Ω · cm, 10 Ω/□ and quite high as 18 dB, respectively.

Optical Transmission and Conductivity of Nematic Liquid Crystals Containing Dispersed Multiwall Nanotubes

Abstract: For nematic liquid crystals (LC) with small (0.01–0.15 wt%) concentration of multiwall nanotubes (NT) dispersed therein, optical transmission and electric conductivity were measured as a function of temperature. Characteristic changes in transmission at the nematic-isotropic phase transition temperature have been noted, suggesting that NT dispersed in the LC matrix behave in a manner similar to that of the conventional non-mesogenic dopants. This picture is supported by the electrical conductivity data. The electrical conductivity increased noticeably within ∼0.01–0.1 wt% range of NT concentrations in the LC matrix, and a marked difference in the measured electrical conductivity values for the LC matrices of different polarity (e.g., cyanobiphenyl and azoxy) was observed.

Characterization of Blue Sensitive Holographic Polymer Dispersed Liquid Crystal for Microholographic Data Storage

Abstract: We present the results of an extended investigation performed on holographic reflection gratings recorded in blue sensitive polymer dispersed liquid crystals in view of a possible application in optical data-storage. The analysis has been performed by means of real-time spectroscopy during the polymerization process. The analysis of transmission spectra during the recording process showed a fast photopolymerization, resulting in the rapid formation of a reflection peak. Gratings characterized by high spatial frequency (> 7000 lines/mm), high diffraction efficiency (up to 50%) and large refractive index modulation (Δn ∼ 0.008) have been obtained. Unfortunately, the monomer conversion into a polymer network is generally characterized by a strong packing, with a consequent reduction in volume (polymerization shrinkage). This phenomenon induces a significant blue-shift of the reflected wavelength. With the aim of better understanding and possibly reducing the shrinkage, a new high-sensitive experimental techn...

Novel Color Changing pH Sensors Based on Cholesteric Polymers

Abstract: Color changing cholesteric hydrogen bonded polymer films responding to pH changes induced by basic amino acids or inorganic bases were synthesized and studied. The films with a higher concentration...

Physical Properties of Multi-Walled Carbon Nanotube-Filled PVDF Composites Prepared by Melt Compounding

Abstract: Multi-walled carbon nanotube (MWNT)/Poly(vinylidene fluoride) (PVDF) composites with various loading levels (0.01 ∼ 10 wt%) have been prepared by the simple melt-compounding approach. Morphology and electrical properties of the composites were investigated. The experimental percolation threshold for the electrical conductivity was estimated and clearly occurred between 2 and 2.5 wt%. MWNT/PVDF composites presented a shoulder posterior to the main melting peak and an increased endpoint of the peak. In the WAXD profiles, the incorporation of MWNT produced a larger shoulder at 2θ = 20.7° with increase in the loading levels, corresponding to the β-form crystal of PVDF. In the rheological properties, dynamic viscosity, the extent of shear thinning behaviors and relaxation time were notably increased with the MWNT content.

Electronic Excitation Energy Transfer in DNA. Nature of Triplet Excitations Capturing Centers

Abstract: Spectral properties, energy structure, and electronic processes in DNA, poly(dAdT)2, d(CCCGGGTTTAAA), d(ATC), d(AT), dGMP, dAMP, dCMP, dTMP were studied. The DNA lowest excited electronic singlet and triplet levels are connected with guanine and adenine bases, correspondingly. The DNA fluorescence is close to a linear combination of the guanine and cytidine emissions and connected, to a greater extent, with the singlet energy transfer to these bases. The origin of the DNA phosphorescence is associated with AT-sequences that are traps of triplet excitations in DNA. The triplet energy transfer to these centers and adenine bases (that are most photostable) leads to the DNA self-protection against a damage induced by electronic excitations of DNA.

Synthesis and Characterization of Novel All-Organic Liquid Crystalline Radicals

Abstract: We have synthesized a new series of all-organic liquid crystalline (LC) radical compounds (2), which are the structural isomers of the previously reported series (1) containing a chiral nitroxide unit in the mesogen core. Only difference between the two isomers is the orientation in the ester functionality (‒OCO‒ vs ‒COO‒). The new LC compounds 2 with C4 to C8 alkoxy terminal chains showed the distinct odd-even effects of alkoxy terminal chains with respect to the thermal stability of nematic phases, while such effects were not observed for the isomers 1.

Glass-Forming Hole-Transporting Triphenylamine-Based Hydrazones with Reactive Functional Groups

Abstract: Synthesis and the properties of a series of triphenylamine-based hydrazones are reported The dependence of their thermal and glass-forming properties on their chemical structure is discussed The ionization potentials of the synthesized hydrazones measured by the electron photoemission technique range from 516 to 532 eV Hole-drift mobilities of some derivatives molecularly dispersed in bisphenol Z polycarbonate exceed 10−4 cm2V−1s−1 at high electric fields (106 V/cm),at room temperature

Synthesis, Characterization, and Mesomorphic Properties of New Liquid-Crystalline Compounds involving Ester–Azomethine Central Linkages, Lateral Substitution, and a Thiazole Ring

Abstract: In continuation with our work on liquid crystals with unconventional molecular structures, two homologous series that have 1,4-disubstitution and 1,3,4-trisubstitution in the central phenyl ring, such as 2[(4-n-alkoxy-benzyloxy) phenyl azomethine]-5-methyl thiazole and 2-[(4-n-alkoxy-benzyloxy)-2-hydroxy salicyladimine]-5-methyl thiazole, have been synthesized. They have been characterized by elemental analysis, FT-IR, 1HNMR, 13CNMR, and mass spectrometry. The liquid-crystalline behavior of these compounds was observed by differential scanning calorimetry (DSC) and polarizing microscopy. All the compounds of the 1,4-disubstituted series show an enantiotropic nematic phase only, whereas the compounds of the 1,3,4-trisubstituted series show smectic and nematic phases. Some mesogens with a lateral hydroxy group were also synthesized to evaluate the effect of this group on melting point, transition temperatures, and mesophase morphology.

Integration of Optical Pumped Dye Laser on Organic Microflowcytometry Chip

Abstract: Integration techniques of tunable film dye laser on a plastic optical application chip were studied. The developed film dye lasers were waveguided distributed feedback (DFB) lasers, and they can cover the wavelength from 400 to 1100 nm. We fabricated microflowcytometry chip integrated with DFB film lasers as a first example. Partly film-coating technique and film lithography fabrication with an excimer laser were tried and combined each other. The film DFB dye laser was found as an useful technique for multi-color laser integration, and they showed comparable performance our traditional spin-coated film dye lasers.

Polarizing Properties of Functional Optical Films Based on Lyotropic Chromonic Liquid Crystals

Abstract: We report results of the optical characterization of dried thin films obtained from the well-aligned nematic phase of a lyotropic chromonic liquid crystal (LCLC) by two different deposition techniques. The first one, the electrostatic layer-by-layer deposition technique, was used to prepare aligned LCLC films of a nanometer thickness in the form of a monomolecular layer and multi-layered stack. The second technique is the direct deposition technique. The films' optical characteristics such as dispersion of the light absorption indices, birefringence, polarizing efficiency, contrast ratio, transmittance of unpolarized light, were measured and compared with the correspondent characteristics of a cell filled with nematic solution of the same LCLC material.

Resistance of a Nanocarbon Material Containing Nanotubes

Abstract: The results of the experimental studies of resistivity of a nanocarbon material (NCM), which contains carbon nanotubes (CNT), and also the amorphous carbon particles and nanographite are presented. The main efforts were aimed at the ascertaining the mechanism of NCM conduction with regard to their phase composition.

Organic Conductor Based on Nucleobase: Structural and Electronic Properties of a Charge-Transfer Solid Composed of TCNQ Anion Radical and Hemiprotonated Cytosine

Abstract: A semiconductive charge-transfer solid was prepared by the reaction of cytosine and TCNQ. Cytosine molecules formed a hemiprotonated cytosine pair by complementary triple hydrogen bonds, and the pairs were then linked by complementary double hydrogen bonds to form infinite ribbons. TCNQ molecules formed uniform segregated columns. The robust hydrogen bonds linking the cytosine and TCNQ molecules preserved the uniform arrangement even at low temperatures. Such structural regulation demonstrated a high conductivity of 3 × 10−2 S cm−1 in a fully ionic TCNQ salt by virtue of large transfer interaction and short interplanar distance of TCNQ molecules.

Photoinduced Deformation Behavior of Crosslinked Azobenzene Liquid-Crystalline Polymer Films with Unimorph and Bimorph Structure

Abstract: The use of a crosslinked azobenzene liquid-crystalline polymer (CALP) system for micro-integrated actuators becomes especially attractive. CALPs can deform along the alignment direction of mesogens upon irradiation of UV/visible light owing to photochemical phase transition. In this study, to improve the bending speed, CALP films with a homogenous alignment on one surface and a homeotropic alignment on the opposite surface (hybrid alignment) were prepared and their bending behavior was investigated. The films showed photoinduced bending whose direction was determined by the surface alignment treatment, and the bending speed was greatly enhanced upon irradiation from both surfaces of the film at the same time.

Tuning Hydrogen-Bonding with Amide Groups for Stable Columnar Mesophases of Triphenylene Discogens

Abstract: Tuning hydrogen-bonding of discotic liquid crystal can result in more ordered columnar mesophases and higher charge carrier mobility materials. In this paper, triphenylene derivatives with one, two and three amide groups with structure of C18H6(OR)5(OCH2CONHBu), C18H6(OC5H11)4(OCH2CONHBu)2 and symmetrical and asymmetrical C18H6(OR)3(OCH2CONHBu)3 (R = C n H2n+1, n = 4–9) respectively were designed and synthesized. The results showed that each intra-columnar H-bond forming amide (–CONH–) group caused an average increase of 22°C in clearing point from the non-H-bonding ester group (–COO–) triphenylene analogous. This was the first quantitative result of H-bonding on the stabilization of columnar mesophase.

Porphyrin-Based Molecular Architectures for Light Energy Conversion

Abstract: We have constructed a series of supramolecular photovoltaic cells composed of multi-porphyrin arrays such as porphyrin-alkanethiolate monolayer protected-gold nanoparticles [H2PCnMPC: n is the number of methylene groups in the spacer], porphyrin dendrimers [D n P n ], and porphyrin-peptide oligomers [P(H2P) n ] and fullerene (C60) on nanostructured SnO2 electrodes (OTE/SnO2). These multi-porphyrin arrays form complexes with fullerene molecules and they form clusters in acetonitrile/toluene mixed solvent. The highly colored composite clusters are assembled as three-dimensional arrays onto nanostructured SnO2 films [denoted as OTE/SnO2/(multi-porphyrin array+C60) m ] using an electrophoretic deposition method. These highly organized molecular assembly films attain drastic enhancement of light energy conversion properties as compared to the non-organized reference system. The maximum power conversion efficiency (η) of OTE/SnO2/(H2PC15MPC+C60) m reaches 1.5%, which is 45 times higher than that of the referenc...

Inverse Frederiks Effect and Bistability in Ferronematic Cells

Abstract: In recent work we have examined switching properties of a ferronematic in an external magnetic field in a cell with homeotropic boundary conditions, and subject also to a bias field in the plane of the cell. There are three regimes, depending on the strength of the director-ferroparticle coupling. For low coupling, there is a high field inverse Frederiks transition to an undistorted phase. At low non-dimensional temperatures, high magnetic fields can cause the ferroparticles to segregate. Segregation-director distortion coupling can drive the inverse Frederiks transition first order, causing bistability. This article considers homogeneous planar, rather than homeotropic anchoring at the cell walls and particle surfaces. The bias field is unnecessary, but the basic physical picture is retained, with the same set of regimes. The lack of bias field means that this case is a more suitable model for basic studies.

New Photoalignment Materials in LCD's Development: Liquid Crystal Pretilt Angle Variations By Using Fluoroalkylmethacrylates

Abstract: Fluorinated copolymers based on 4-(N-methacryloylamino)phenyl methacrylate are proposed as materials for the liquid crystal (LC) photoalignment with a wide range of variations of a pretilt angle. As fluorinated chains, 2,2,3,3-tetrafluoropropylmethacrylate and 2,2,3,3,4,4,5,5-octafluoropenthylmethacrylate are used. The growth of a pretilt angle with the concentration of fluorinated chains, more pronounced in a series with longer fluorinated chain, is observed. The pretilt angle of TN LC ZLI 2293 is smoothly varied in the range 0°–20°. Additionally, the uniform high pretilt angle (89°–90°) alignment is realized for VA LC MJ961180.

On the Importance of the Molecular Core Interactions on the Induction of the High Optical Tilt Angle

Abstract: Two smectogens being structural analogs with the opposite space orientation of the COO ester group in the molecular core exhibit extremely different tilt angles. A molecular mechanism of the induction of the high optical tilt angle is searched on the basis of extensive investigations of those compounds. Computer modeling of molecules and investigations of physical parameters of smectic phases were done. Different molecular aggregates forming smectic phases were observed. The size and shape of those aggregates are estimated on the basis of measurements and calculations. The different values of the tilt angles in studied compounds were discussed.

High figure-of-merit laterally fluorinated biphenyltolane-isothiocyanates

Abstract: We have designed, synthesized, and evaluated the physical properties of some high birefringence (Δn) isothiocyanato biphenyl-tolane liquid crystals. These compounds exhibit Δn ∼ 0.48–0.52 at room temperature and wavelength λ = 633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. A eutectic mixture based on those compounds was formulated and its physical properties evaluated.

SEM Investigations of the Polymer Morphology in the Liquid Crystal-Polymer Composites with Different Polymer Contents

Abstract: Scanning electron microscopy was employed to study the evolution of the morphology of liquid crystal-polymer composites with increasing contents of a polymer. The composites were formed by a nematic mixture E7 from Merck and a photocurable adhesive NOA65 from Norland by means of photoseparation. The polymer phase reveals a smooth transition from a polymer network to a sponge-like structure and then to the ‘Swiss cheese’ morphology with the increasing fraction of a polymer. It is established that the best electro-optic performance is demonstrated by samples with the well-developed sponge-like structure of the polymer phase.

Microcapsules by Complex Coacervation for Electronic Ink

Abstract: Electrophoretic TiO2 nanoparticles in a low dielectric medium can be utilized in non-emissive flexible display such as an electronic paper. To prevent the aggregation and to reduce the density of neat TiO2 nanoparticles, the surface of TiO2 particles was modified by acrylic copolymer. The surface modified TiO2 nanoparticles, which were dispersed in low dielectric oils, were encapsulated by the complex coacervation of gelatin and gum Arabic. Then, core-shell type microcapsules were eventually fabricated. The capsules were crosslinked by the reaction between glutaraldehydes and amino groups in gelatinto improve the durability of the microcapsules. These microcapsules were stable during vacuum drying and were easily layered on the surface of the ITO substrates because of their flexibility. A simple electrophoretic display cell was constructed and both the color change and the response time were monitored.

Confocal Microscopy of Director Structures in Strongly Confined and Composite Systems

Abstract: We review approaches for simultaneous imaging of three-dimensional director structures and component distributions in composite materials using fluorescence confocal polarizing microscopy. To study dynamic processes in these systems, we use the Nipkow-disk microscope in which the confocal images are obtained within milliseconds. The visualized director fields, free-standing film profiles, and ordered colloidal structures provide insights into the physics phenomena ranging from elasticity-mediated self-organization to anchoring-assisted levitation and dynamics of micron-sized spheres.