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Showing papers in "Molecular Crystals and Liquid Crystals in 2000"


Journal ArticleDOI
TL;DR: In this article, the authors have analyzed flammability of polypropylene (PP)/cellulose composites with long flax fibers obtained by compressing and showed that thermal decomposition and combustion of the mentioned samples occur in a different way.
Abstract: Biodegradability and interesting physical and mechanical properties of polypropylene (PP)/cellulose composites are the essential motive for undertaking fundamental studies of various properties of such materials. An addition of lignocellulosic particles to polymers results in a change in properties of the product obtained which is a resultant of properties of lignocellulosic material and those of polymer and depends on the proportion of both materials. It is also reflected in the flammability characteristics of the composites. In this study we have analyzed flammability of PP composites with long flax fibers obtained by compressing. The amounts of natural fibers were 12.5%, 20%, 30% and 40%. The thickness of the investigated samples was 5 mm. The samples were tested in accordance with ISO 5660 (Cone Calorimeter) at heat flux of 35 kW/m2. Heat release rate (HRR) and mass loss rate (MLR) curves show that thermal decomposition and combustion of the mentioned samples occur in a different way. When fl...

49 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used aspen fiber and polypropylene to construct a composite with and without the addition of a compatibilizer (maleic anhydride grafted polyethylene, MAPP).
Abstract: Natural fiber/thermoplastic composites were made using aspen fiber and polypropylene. Several different levels of aspen fiber (30 to 60% by weight) were used with and without the addition of a compatibilizer (maleic anhydride grafted polypropylene, MAPP). These composites were tested for strength properties, exposed to boiling and cyclic liquid water and oven drying tests, and evaluated in an accelerated weathering test for 2000 hours. As the level of fiber increases without MAPP, flexural strength, flexural modulus, tensile strength and tensile modulus increases but notched and unnotched impact strength decrease as compared to pure polypropylene. The presence of MAPP has a very large positive effect on flexural strength, flexural modulus, tensile strength and tensile modulus as compared to composites made without MAPP. As the level of fiber increased in the composites, the rate and extent of thickness swelling and moisture sorption increased as compared to pure polypropylene. The presence of MAP...

49 citations


Journal ArticleDOI
TL;DR: Hybrid inorganic-organic polymers (ORMOCER®s) have been developed and tested for evaluation in optical and electrical interconnection technology as discussed by the authors, which are composed of inorganic oxidic structures cross-linked or substituted by organic groups.
Abstract: Hybrid inorganic-organic polymers (ORMOCER®s) have been developed and tested for evaluation in optical and electrical interconnection technology. The photopatternable materials with negative resist behaviour are composed of inorganic oxidic structures cross-linked or substituted by organic groups. They are prepared from organosilane precursors by sol-gel-processing in combination with organic crosslinking of polymerizable organic functions. As a result of these functionalities the properties of the ORMOCER®s can be adjusted to particular applications. Systematic variation of composition combined with adaptation to micro system technology allows great flexibility in processing. The main features of these materials are: Combined use as dielectric and passivation layers in electrical systems and devices as well as core and cladding for optical applications enables e/o applications with high integration levels. Postbaking at moderate temperatures (120°C – 170°C) enables processing on low-cost substra...

48 citations


Journal ArticleDOI
TL;DR: In this article, the solid state structures of a series of methyl substituted neutral quaterthiophenes have been analyzed in terms of crystal cohesion and intermolecular interactions.
Abstract: The solid state structures of a series of methyl substituted neutral quaterthiophenes have been analysed. Structures have been retrieved from the Cambridge Structural Database and investigated in terms of crystal cohesion and intermolecular interactions. In these thiophene oligomers, it can be shown that crystal packing efficiency and optimisation of S—S, C-H—S and C-H—π interactions constitute the driving force for their solid state geometry and configuration. A detailed discussion of their packing arrangement is reported and shown to be based on either a herringbone or π-π stacking of thiophene units.

45 citations


Journal ArticleDOI
TL;DR: Semi-flexible copolyimides with various alkyl chain lengths (BTDA-ODA/CnMPD PIs) were newly synthesized in N-methyl-2-pyrrolidone from benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphenylene diamine, and 3,5-diaminobenzoyl n-alkanoates.
Abstract: Semi-flexible copolyimides with various alkyl chain lengths (BTDA-ODA/CnMPD PIs) were newly synthesized in N-methyl-2-pyrrolidone from benzophenonetetracarboxylic dianhydride, 4,4′-oxydiphenylene diamine, and 3,5-diaminobenzoyl n-alkanoates. The films were rubbed with varying rubbing densities, and on the rubbed surface the alignment behavior of a nematic liquid-crystal (LC) was examined. LCs were always aligned along the rubbing direction either homogeneously or homeotropically, depending on the side chain length as well as the rubbing density. The results inform that flexible n-alkyl side groups in the copolyimide play a critical role to align LCs on the surface, and their role is strongly dependent on its length. In addition, thermal, optical, and dielectric properties were investigated.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of defects in the bulk and at the domain boundary on carrier transport was investigated by measuring transient photocurrents in thick cells up to 120 μm in thickness and in the cells of different domain sizes of 10−100s μm.
Abstract: Smectic mesophases in the calamitic liquid crystalline materials such as 2-phenylnaphthalene derivatives exhibit fast ambipolar carrier transport, whose mobility is up to 10−2 cm2/Vs. For these mesophases, we have investigated the effect of defects in the bulk and at the domain boundary on these carrier transport by measuring transient photocurrents in thick cells up to 120 μm in thickness and in the cells of different domain sizes of 10–100s μm. It was found that non-dispersive carrier transports was observed for all the cells and the carrier transport was affected neither by cell thickness nor by domain sizes. Thus, it was concluded that there are few deep defects in the bulk and that the domain boundary is electrically inactive in these mesophases, demonstrating their high potential for practical application to large-area electronic devices.

42 citations


Journal ArticleDOI
TL;DR: Tetra and octa(13, 17-dioxa nonacosane-15-sulfanyl) substituted metal free-and Ni(II) phthalocyanines have been synthesized from the corresponding phthalonitrile derivatives in the presence of the anhydrous metal salt (NiCl2) or a strong organic base.
Abstract: Tetra- and octa(13, 17-dioxa nonacosane-15-sulfanyl) substituted metal free- and Ni(II) phthalocyanines have been synthesized from the corresponding phthalonitrile derivatives in the presence the anhydrous metal salt(NiCl2) or a strong organic base. The new compounds have been characterised by elemental analyses, IR, NMR and electronic spectroscopy and mass spectra. The mesogenic properties of these new materials were studied by differential scanning calorimetry(DSC), optical microscopy and X-ray investigations. All compounds show a discotic mesophase in an extremely large temperature interval including room temperature. X-ray diffraction patterns of the mesophases confirm that tetra-substituted compounds(5a, 5b) form a hexagonal ordered columnar mesophases(Dho), whereas octa-substituted compounds(7a, 7b) lead to centered rectangular disordered columnar mesophases(Drd).

42 citations


Journal ArticleDOI
TL;DR: In this paper, a bio/organic-inorganic hybrid compound of deoxyribonucleic acid (DNA) and methotrexate (MTX)-layered double hydroxide is prepared by ion exchange type intercalation reaction.
Abstract: Novel bio-/organic-inorganic hybrid compounds of deoxyribonucleic acid (DNA) and methotrexate (MTX)-layered double hydroxide are prepared by ion-exchange type intercalation reaction. The layered inorganic support. Mg2Al(NO3)-LDH, is at first obtained by coprecipitation in an aqueous solution, and then the interlayer NO3 − anions are replaced by guest molecules such as methotrexate (an anticancer drug) and deoxyribonucleic acid (about 500 ∼ 1000 base pairs), leading to form new bio-/organic-nanohybrids. Upon intercalating guest molecules into hydroxide layers, the basal spacing of LDH increases from 8.5 A (NO3 −) to 20.8 A (MTX) and 23.9 A (DNA), respectively. According to the X-ray diffraction and infrared spectroscopic analyses, it is found that the target molecules are safely preserved by hydroxide layers maintaining their chemical and structural properties.

41 citations


Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the dispersion and transient current profiles of two classes of liquid crystal substances and provided an idea of probable mechanisms of ion generation, such as the dissociation of ion pairs and the recombination of free ions.
Abstract: Permittivity dispersion and transient current profiles of two classes of liquid crystal substances were analyzed, providing an idea of probable mechanisms of ion generation. Due to the strong local field caused by the electric double layers by ions, Schottky injection at electrodes can play an important role even under a small DC voltage application. In a higher voltage region, the dissociation of ion pairs and the recombination of free ions can be the dominant mechanisms, resulting in the Ohmic behavior of the voltage dependence of a steady-state current. Understandings of those mechanisms will be of a great help for development of advanced liquid crystal materials for uses in sophisticated displays.

40 citations


Journal ArticleDOI
Barry Van Gemert1
TL;DR: In this article, the authors reflect back on commercial uses that have developed from this interesting class of organic compounds over the years, including security devices and optical memory storage, the one application that has achieved substantial commercial success is switchable lenses.
Abstract: With 1999 marking the 100th anniversary of the discovery of organic photochromic compounds1, it is a fitting time to reflect back on commercial uses that have developed from this interesting class of organic compounds over the years. From the many applications that have been proposed, including security devices and optical memory storage, the one application that has achieved substantial commercial success is switchable lenses. Such lenses, based on inorganic photochromes (AgX), have been available since the mid 1960s, but it is only in the last 10 years that organic systems with acceptable performance have been available in the marketplace. From the mid 1980s until his sudden death in early 1998, John Crano lead the research effort at PPG Industries that developed the photochromic systems that have been commercialized by Transitions Optical Inc. under the name Transitions®.

40 citations


Journal ArticleDOI
TL;DR: In this article, a graphite with H2SO4 was thermally expanded at 1000°C and the surface area and chemical character of the exfoliated graphite was investigated.
Abstract: Electrochemically intercalated graphite with H2SO4 was thermally expanded at 1000°C. Exfoliated samples of GIC-H2SO4 with different times of expansion revealed different expansion volumes. Both the surface area and the chemical character of samples also depend on the exfoliation time. A low density of the exfoliated graphite is demanded for the oil sorption. The oil sorption is restricted by the surface area and the bulk density.

Journal ArticleDOI
TL;DR: In this paper, the structures of the higher fullerenes with the sizes of C86 and C88 are described based on UV/Visible/nearIR absorption spectra and 13C NMR measurements in solution.
Abstract: The isomer structure and stability of higher fullerenes is one of the most interesting issues which might be closely related with general question how a fullerene cage structure is formed. In the present study, the structures of the higher fullerenes with the sizes of C86 and C88 are described based on UV/Visible/nearIR absorption spectra and 13C NMR measurements in solution. For well-understanding the structure and growth of higher fullerenes, the isomer-free samples were prepared for all isomers associated with the C86, and C88 cages by means of a multiple stage high performance liquid chromatography (HPLC). As a result, five different isomers for C86 and C88 were successfully isolated and characterized. For these five different isomers studied in the present work, 13C NMR measurements in solution straightforwardly gave a conclusion that three of them possess the cage structures with a C2 molecular symmetry and two with a Cs molecular symmetry. The possible specific candidates for these five is...

Journal ArticleDOI
TL;DR: In this article, metal-free phthalocyanine derivatives were characterized both thermotropic and lyotropic mesophases by DSC and X-ray, and they carried four or eight oligo(ethyleneoxy)thia groups on peripheral positions.
Abstract: Metal-free phthalocyanines and nickel phthalocyanines carrying four or eight oligo(ethyleneoxy)thia groups on peripheral positions have been synthesized from new phthalonitrile derivatives. These phthalocyanine derivatives were characterized both thermotropic and lyotropic mesophases by DSC and X-ray.

Journal ArticleDOI
TL;DR: In this paper, a π-conjugated Ru(II) dinuclear complex containing a new azobenzene-bridged bis(terpyridine) ligand was synthesized and its photochemical and electrochemical properties were investigated.
Abstract: A novel π-conjugated Ru(II) dinuclear complex containing a new azobenzene-bridged bis(terpyridine) ligand was synthesized and its photochemical and electrochemical properties were investigated. The ligand underwent reversible trans-cis photoisomerization, whereas the Ru complex did not show such photoisomerization behavior. Cyclic voltammetry of the complex displayed a reversible one-step 2e oxidation wave due to Ru(III)Ru(III)/Ru(II)Ru(II) and four le reduction waves indicating the formation of mixed-valence states when the electrons are accumulated at the ligand-based orbitals.

Journal ArticleDOI
TL;DR: The literature states that serious decay occurs when the moisture content of wood is above the fiber saturation point (FSP), which is known as the saturation point of wood fiber as mentioned in this paper.
Abstract: Moisture content has an effect on the biological decay of wood. The literature states that serious decay occurs when the moisture content of wood is above the fiber saturation point (FSP), which is...

Journal ArticleDOI
TL;DR: In this paper, a series of dimeric compounds, which comprise the schiff's base mesogen, alkyl spacer with the carbon number of 5 and alkyyl or alkoxy tail with the Carbon number of m = 4∼16, were found to be antiferroelectric.
Abstract: We have prepared two series of dimeric compounds, which comprise the schiff's base mesogen, alkyl spacer with the carbon number of 5 and alkyl or alkoxy tail with the carbon number of m = 4∼16. In these compounds, we observed three types of smectic liquid crystals, the single layer phase with the tail group randomly mixing with the spacer, the bilayer phase in which the segregation of the spacer and tail groups takes place and so two mesogenic layers are included within a repeat unit, the frustrated smectic phase in which the density modulation appears along the layer as well as the layer normal. The bilayer phase was found to be antiferroelectric and the frustrated smectic phase was considered to result from the two dimensional escape from the dipolar interaction. The phase behaviour with m and the structure and properties of each phase will be described in detail.

Journal ArticleDOI
TL;DR: In this paper, the nature of jute fiber, productivity, advantages, disadvantages, its composition etc have been described and compared with the glass fiber, and the role of Jute composite as wood substitute is explained.
Abstract: This article consists of the two parts. In the first part the nature of jute fiber, productivity, advantages, disadvantages, its composition etc. have been described. The jute fiber is also compared with the glass fiber. Inspite of some advantages, this natural fiber possess some drawbacks and thus needs chemical modification. For modification of fiber-matrix interaction i.e.to reduce jute polymer interactions and to facilitate wetting, the use of compatibilisers is also mentioned. In the second part different types jute composites have been described. The role of jute composite as wood substitute is explained. The different methods of jute composite manufacture with its potentials & prospects are also described in a nutshell.

Journal ArticleDOI
TL;DR: In this article, a simple mechanistic model for the ring opening/closing reaction in room temperature solution was proposed for 3,3-diphenylnaphtho[2,1-b] pyran in solution.
Abstract: Transient absorption spectroscopy with femtosecond time resolution was used to probe the photochemical ring opening process of 3,3-diphenylnaphtho[2,1-b] pyran in solution. Analysis of the temporal evolution of the spectra from 0.4 ps to 100 ps has allowed us to detect and identify some of the intermediates involved in the photochemical formation of colored photomerocyanine isomers. From these data and those of recent ab initio and semi-empirical calculations on related photochromic systems, a simple mechanistic model was proposed for the ring opening/closing reaction in room temperature solution.

Journal ArticleDOI
TL;DR: In this article, the authors describe the chemical, thermal and thermomechanical characterization of curaua fiber, which is of major interest in several applications, and the large temperature range to which the fibers are submitted.
Abstract: This paper describes the chemical, thermal and thermomechanical characterization of curaua fiber. The research of the thermal and thermomechanical properties of natural fibers is of major interest, considering their increasing utilization in several applications, and the large temperature range to which the fibers are submitted.

Journal ArticleDOI
TL;DR: In this paper, two approaches to synthesize hybrid organic-inorganic materials are presented: the hydrolysis of organo functional metal alkoxides or the assembly of nanobuilding blocks.
Abstract: Among other soft chemistry processes, sol-gel chemistry offers a versatile access to chemically designed new hybrid organic-inorganic materials. Two approaches to synthesize hybrids are presented: the hydrolysis of organo functional metal alkoxides or the assembly of nanobuilding blocks.

Journal ArticleDOI
TL;DR: In this paper, the authors show that by favoring a pitch gradient in the helix during a novel experimental process, it is possible to get a cholesteric glassy material whose spectral characteristics evolve from a selective to a broad-band filter.
Abstract: Due to the existence of a macroscopic helicoidal structure, cholesteric liquid crystals exhibit many remarkable properties like selective light reflections. Bragg reflections occur when the helix pitch is of the order of the wavelength of the incident light propagating along the helix axis. The wavelength bandwidth is due to the medium birefringence and is typically limited to 50 nm, which is insufficient for some applications (full-colors displays, for example). The purpose of this paper is to show that, by favoring a pitch gradient in the helix during a novel experimental process, it is possible to get a cholesteric glassy material whose spectral characteristics evolve from a selective to a broad-band filter. Light reflection occurs on several hundreds of nanometers and several intermediary optical states are available during a thermal treatment. From a reciprocal viewpoint, the inverse transition, from a broad- to a narrow-band filter, is also demonstrated. Such a process is driven by one para...

Journal ArticleDOI
TL;DR: In this paper, the authors focus their attention on the family of distorted Mn4 cubane molecules with a [MnIVMnIII 3O3X]6+ core, tetranuclear vanadium (III) complexes with a butterfly structure and dodecanuclear manganese complexes, and their corresponding singly reduced salts (PPh4) which have been extensively studied in our laboratories.
Abstract: Metal cluster complexes with interesting magnetic properties characteristic of nanoscale magnetic particles have become an attractive prospect in the last few years. These complexes exhibit magnetization hysteresis loops and out-of-phase ac magnetic susceptibility signals. The advantages of such clusters over fragmented bulk ferromagnets are their easy synthesis and manipulation, their high solubility, and their potential use in storing a large density of information. Here we will focus our attention on the family of several distorted Mn4 cubane molecules with a [MnIVMnIII 3O3X]6+ core, tetranuclear vanadium (III) complexes with a butterfly structure and dodecanuclear manganese complexes, [Mn12O12(O2CR)16(H2O)4] (where R can be an aliphatic or aromatic group) and their corresponding singly reduced salts [Mn12O12(O2CR)16(H2O)4] (PPh4), which have been extensively studied in our laboratories.

Journal ArticleDOI
TL;DR: In this paper, the dependence of the photo-orientation process on the liquid crystallinity and the molecular aggregation is studied, and it is shown that the optical anisotropy increases with spacer length or the ordering tendency of the polymers.
Abstract: The dependence of the Photo-orientation process on the liquid crystallinity and the molecular aggregation is studied. In the case of ordered films the photo-orientation is restricted, but this restriction can be overcome by a photochemical pre-treatment using UV light or by higher power density of the incident Vis light. The optical anisotropy increases with spacer length or the ordering tendency of the polymers.

Journal ArticleDOI
TL;DR: In this article, 3,3-Diphenyl-9,10-di-n-undecyloxypyrano[3,2-a]phenazine 3 was designed to be incorporated into fibres of 2.3-di.n.undecyclicoxyphenazine which display gel-forming ability in various fluids.
Abstract: 3,3-Diphenyl-9,10-di-n-undecyloxypyrano[3,2-a]phenazine 3 was designed to be incorporated into fibres of 2,3-di-n-undecyloxyphenazine which display gel-forming ability in various fluids. A spectrok...

Journal ArticleDOI
TL;DR: The bis-μ-dicarboxylate ruthenium (II,III) complexes, Ru 2L2Br (L = trans-O2C-CH-CH═CH-CO2 (1), trans-transtrans-O 2C-C6H4-CO 2 (2), and p-o2C -C6h4- CO 2 (3), were prepared and their gas-occlusio...
Abstract: The bis-μ-dicarboxylate ruthenium (II,III) complexes, Ru (II,III)2L2Br (L=trans-O2C-CH═CH-CO2 (1), trans-trans-O2C-CH═CH-CH═CH-CO2 (2), and p-O2C-C6H4-CO2 (3)), were prepared and their gas-occlusio...

Journal ArticleDOI
TL;DR: A comparison between M.L.C. and parent intercalated layered binary systems shows comparabl... as discussed by the authors, showing that the stability of misfit layer chalcogenides is always governed by a charge transfer mechanism.
Abstract: Stability of misfit layer chalcogenides (M.L.C.) is always governed by a charge transfer (C.T.) mechanism. A comparison between M.L.C. and parent intercalated layered binary systems shows comparabl...

Journal ArticleDOI
TL;DR: In this paper, the effects of fluorine-inherited sp 3-carbon sites on the electronic state of the nano-sized π-electron system were investigated, showing that the orbital diamagnetism is monotonically reduced with increasing F/C, suggesting that introduced sp 3 carbon sites make the extended πconjugated system reduced.
Abstract: Activated carbon fibers (ACFs) are microporous systems comprised of a random network of nano-sized graphites. We investigated the structure and electronic properties of fluorinated ACFs in order to clarify the effects of fluorine-introduced sp 3-carbon sites on the electronic state of the nano-sized π-electron system. The orbital diamagnetism is monotonically reduced with increasing F/C, suggesting that introduced sp 3 carbon sites make the extended π-conjugated system reduced. In the intermediate fluorine concentration region, the localized spin concentration is enhanced by fluorination, reaching a maximum at F/C ∼ 0.8, whereas it tends to be lowered in the high concentration region. The enhancement in the spin concentration is explained in terms of the local destruction of the π-conjugated system at interior carbon sites by fluorine-inherited sp 3-carbon sites.

Journal ArticleDOI
TL;DR: Wood-polymer composites (WPC) as discussed by the authors are made from wood and monomers that are polymerized inside the wood, combining wood with polymer enhances the physical properties of the wood allowing the composite to be tailored to specific applications.
Abstract: Wood-polymer composites (WPC) are made from wood and monomers that are polymerized inside the wood. Combining wood with polymer enhances the physical properties of the wood, allowing the composite to be tailored to specific applications. This paper reviews the processes and monomers used to make WPC, physical properties of WPC, and actual and potential applications. The characteristics of traditional monomers (methyl methacrylate and styrene) and new monomers are described, as are WPC surface hardness, water repellency, dimensional stability, abrasion resistance, and fire resistance. Current and potential uses for WPC range from hardwood flooring to furniture, sports equipment, parts for musical instruments, industrial applications, and construction materials.

Journal ArticleDOI
TL;DR: In this article, the tensile strength, electrical resistivity, compressibility, elastic recovery, and Young's modulus of graphite foils were studied as a function of the production conditions.
Abstract: The tensile strength, electrical resistivity, compressibility, elastic recovery, and Young's modulus of foils were studied as a function of the production conditions of graphite foils (the foaming temperature of oxidized graphite, the fraction consumption of graphite, the nature of graphite intercalation compounds and their stage number).

Journal ArticleDOI
TL;DR: In this paper, the authors measured the azimuthal anchoring strength and easy axis gliding of the nematic 5CB on weakly anisotropic substrate and studied the anchoring evolution at a time scale ranging from a few minutes up to a few months.
Abstract: We measure the azimuthal anchoring strength and easy axis gliding of the nematic 5CB on weakly anisotropic substrate. We study the anchoring evolution at a time scale ranging from a few minutes up to a few months. We separate approximately the elastic and the viscous response and we obtain the gliding velocity as a function of the applied torque. We discuss the observed gliding times and nonlinear gliding viscosity.