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Showing papers in "Molecular Crystals and Liquid Crystals in 2008"


Journal ArticleDOI
TL;DR: In this article, the reaction to fire of polymer nanocomposites (thermoplastic polyurethane, polylactide and polyamide-6) containing different nanofillers (organoclay, polyhedral silsesquioxanes or POSS and carbon nanotube) is investigated.
Abstract: In this work, the reaction to fire of polymer nanocomposites (thermoplastic polyurethane, polylactide and polyamide-6) containing different nanofillers (organoclay, polyhedral silsesquioxanes or POSS and carbon nanotube) is investigated. When high level of nanodispersion is achieved (shown by transmission electron microscopy (TEM)), they exhibit good flame retardancy in specific scenarii (high heat flux), but fail to flammability tests (LOI, UL-94). The mechanism of protection is the formation of mineral layer associated to char promotion but the protective coating is not efficient enough to provide the highest standard of protection. It is shown that this technology gives the best results combined with conventional flame retardants and leads to synergistic effects. The aspects of nanodispersion of the filler with the flame retardant are also fully commented in the paper using TEM and electron microprobe.

116 citations


Journal ArticleDOI
TL;DR: The first processes for wood modification with furfuryl alcohol were developed several decades ago as discussed by the authors, and new catalytic systems and process additives have been developed over the last decade.
Abstract: The first processes for “furfurylation” of wood (wood modification with furfuryl alcohol) were developed several decades ago. Furfuryl alcohol is a renewable chemical since it is derived from furfural, produced from hydrolysed biomass waste. Over the last decade modernised processes for furfurylation of wood have been developed. These new processes are based on completely new catalytic systems and process additives. The properties of furfurylated wood depend on the retention of grafted/polymerised furfuryl alcohol (PFA) in the wood. At high modification levels (high retention of PFA) the enhancement of a wide variety of properties are achieved: an exceptional hardness increase, exceptional resistance to microbial decay and insect attack, high resistance to chemical degradation, increase in MOR and MOE, and high dimensional stability. At lower modification levels many property enhancements also occur, however to slightly lower extent. Notable are resistance to microbial decay and insect attack, increase in...

81 citations


Journal ArticleDOI
TL;DR: In this article, the application of nanolignin as a UV blocker for linen fabrics was described, and the linen fabrics covered by nanlignin showed also antibacterial properties, and it is possible to obtain multifunctional textile products with the following additional properties: UV barrier, antibacterial, antistatic properties guaranteeing positive effect on human physiology.
Abstract: Efficient protection against harmful UV radiation for human can be ensured by wearing garment made from bast fibers: linen and hemp, which also provide high use comfort thanks to high hygroscopicity, air permeability and cool touch. This paper describes application of nanolignin as a UV blocker for linen fabrics. Lignin with nano structure obtained by ultrasonic treatment was padded on linen fabrics. The linen fabrics covered by nanolignin show also antibacterial properties. Thanks to nanolignin application for finishing process of linen fabrics, it is possible to obtain multifunctional textile products with the following additional properties: UV barrier, antibacterial, antistatic properties guaranteeing positive effect on human physiology.

79 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that the strain response of conducting polymers and composites on woven textiles depends on the detailed distribution of the sensor material on the yarn and that the structure of most textiles, with strong fibers twisted into yarns, can provide a support which allows electronic materials, impregnated into the yarn, to stretch and bend without breaking.
Abstract: Metallic connections and polymer sensors have been printed onto textiles as a step toward the production of flexible printed electronics. We show that the strain response of conducting polymers and composites on woven textiles depends on the detailed distribution the sensor material on the yarn. The structure of most textiles, with strong fibers twisted into yarns, can provide a support which allows electronic materials, impregnated into the yarn, to stretch and bend without breaking.

73 citations


Journal ArticleDOI
TL;DR: In this paper, a very thick codeposited i-interlayer reaching 1.2μm was successfully fabricated by using fullerene purified by means of the single-crystal formed sublimation.
Abstract: p-i-n organic solar cells having very thick codeposited i-interlayer reaching 1.2 μm were successfully fabricated by using fullerene purified by means of the single-crystal formed sublimation. Short-circuit photocurrent density of 19 mAcm−2 and photo-electric conversion efficiency of 5.3% were observed.

65 citations


Journal ArticleDOI
TL;DR: In this article, the results of starch and starch derivatives-based electrolytes, which were characterized by impedance spectroscopy and thermal analysis, varied from 10−6 to 10−4 S/cm at room temperature, depending on the sample, and increased following Arrhenius model.
Abstract: Natural polymers are a very interesting matrix to obtain solid polymeric electrolytes (SPE). The principal advantage comes from their particularly interesting biodegradation properties due to the natural origin and also very low cost and good physical and chemical properties. These polymers contain heteroatoms in their structure and for this reason can interact with protons or lithium ions leading to the ionic conduction. Among different natural polymers, starch-based SPEs show good opto-electrochemical characteristics and can be applied to electrochemical devices. This work presents the results of starch and starch derivatives-based electrolytes, which were characterized by impedance spectroscopy and thermal analysis. The ionic conductivity results obtained for these SPEs varied from 10−6 S/cm to 10−4 S/cm at room temperature, depending on the sample, and increased following Arrhenius model. The samples showed good stability up to 200°C evidenced by thermal analysis (TGA). Good conductivity results combi...

62 citations


Journal ArticleDOI
TL;DR: In this article, the electro-optical response and the microstructure of multiwalled carbon nanotubes dispersed in nematic liquid crystals with negative dielectric anisotropy are investigated.
Abstract: The electro-optical response and the microstructure of multiwalled carbon nanotubes dispersed in nematic liquid crystals with negative dielectric anisotropy are investigated. In contrast to undoped liquid crystals, the liquid crystal dispersions of carbon nanotubes are characterized by the irreversible electro-optic response or the so-called electro-optical memory effect. This effect is that the light transmittance through the sandwiched layer of the dispersion placed between two crossed polarizers considerably increases after the electric field application cycle. The state of memory persisted over months of our observation. The memory is caused by the incomplete relaxation of liquid crystal molecules from the random planar to the initial homeotropic state after the field is off. It is pointed out that the stabilization of the planar state is due to the network of small nanotube aggregates formed in the liquid crystal disturbed by electro-hydrodynamic flows. It is revealed that the efficiency of electro-o...

60 citations


Journal ArticleDOI
TL;DR: In this paper, two structurally similar homologous series of chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described and their synthetic routes and mesomorphic properties, such as phase transitions temperatures and enthalpies, are characterized by polarizing optical microscope and differential scanning calorimetry.
Abstract: Two structurally similar homologous series of chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their synthetic routes and mesomorphic properties, such as phase transitions temperatures and enthalpies, are characterized by polarizing optical microscope and differential scanning calorimetry.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the q-plate converts the variation of spin angular momentum associated with the switching of light polarization handedness into orbital angular momentum, an optical process that had not been envisioned before.
Abstract: The helical modes of an electromagnetic wave are characterized by a helical shape of the wavefront. They carry quantized angular momentum of an orbital kind, as opposed to the spin-like angular momentum that can be associated with circularly polarized waves. Here, I review recent results on a novel method for generating helical waves of light by letting a circularly-polarized non-helical wave pass through an azimuthally inhomogeneous birefringent plate made of a suitably patterned liquid crystal, a device dubbed “q-plate”. The q-plate converts the variation of spin angular momentum associated with the switching of light polarization handedness into orbital angular momentum, an optical process that had not been envisioned before. Generalizing this idea, patterned birefringent plates similar to q-plates may be used for shaping the optical wavefront of a circularly polarized beam in any prescribed way. Moreover, these plates allow fast switching between conjugate wavefronts by inverting the handedness of the...

57 citations


Book ChapterDOI
TL;DR: In this article, composites with polypropylene and cellulose microfibrils were characterized by MS-coupled simultaneous TGA-DSC and the reinforcing effect of cellulose was emphasised by mechanical characterization.
Abstract: Polypropylene-based composites containing 10–30% by weight cellulose microfibrils were studied. Composites with polypropylene and cellulose microfibrils were characterised by MS-coupled simultaneous TGA-DSC and the reinforcing effect of cellulose microfibrils was emphasised by mechanical characterization. Experimental results are discussed in connection with the composite preparation method by mixing and extrusion. The effect of cellulose on the thermal stability and degradation behaviour of the polypropylene matrix is pointed out.

53 citations


Journal ArticleDOI
TL;DR: In this paper, the positions and intensities of the absorption bands in the electronic spectrum of benzene ring-based mono-azo dyes were modeled numerically, while preserving their potential mesogenic ability.
Abstract: The study reported herein is focused on measuring, as well as on modeling numerically, the positions and intensities of the absorption bands in the electronic spectrum of benzene ring-based mono-azo dyes, while preserving their potential mesogenic ability. Both non-polar structures, as well as highly polar push-pull structures, of azo dye molecules were designed and studied.

Journal ArticleDOI
TL;DR: In this article, four pyridine-based derivatives (I 10, I 12, I 14, and I 18) with molecular formula CnH2n+1O-C6H4COOC6H 4-N = N-C5H4N, that differ from each other in the number of carbon atoms, n, were prepared and characterized for their mesophase behavior.
Abstract: Four pyridine-based derivatives (I 10, I 12, I 14, and I 18) with molecular formula CnH2n+1O-C6H4COOC6H4-N = N-C5H4N, that differ from each other in the number of carbon atoms, n, were prepared and characterized for their mesophase behavior. The number of carbons in the alkoxy chain varies between 10, 12, 14, to 18 atoms, respectively. Liquid crystalline properties were studied for two series of hydrogen-bonded liquid crystal complexes, consisting of the central 4-pyridylazophenyl benzoate and substituted benzoic acids. In the first series of the supramolecular complexes (group A), the lengths of the alkoxy chains on both of the azo pyridine and the benzoic acid components have varied between 10, 12, 14, and 18 carbons. In the second series (group B), the same proton-acceptors, i.e., the pyridyl azo derivatives, were used but with benzoic acids para-substituted with small compact polar groups, X. All of the newly prepared pyridine-based derivatives and their hydrogen-bonded complexes were found to be meso...

Journal ArticleDOI
TL;DR: In this paper, the effect of carbon nanotube on the crystal structure and mechanical/ferroelectric/piezoelectric properties based on poly(vinylidene fluoride) and carbon nano tube (CNT) composite film was investigated.
Abstract: We investigated the effect of carbon nanotube on the crystal structure and mechanical/ferroelectric/piezoelectric properties based on poly(vinylidene fluoride) (PVDF) and carbon nano tube (CNT) composite film. The composite films were prepared by solution blending method, and the films were formed by hot-pressing. The contents of CNT were from 0.001 wt.% to 1 wt.%. For inducing piezoelectric beta-crystal structure, the hot-pressed nano composite films were drawn by 400% elongation. These samples were poled at high voltage and high temperature for polarization of the PVDF/CNT composite film. The beta-crystalline phase were increased with CNT contents, passing through the peak, and decreased. The structural changes depend on the CNT contents, drawing and poling conditions.

Journal ArticleDOI
TL;DR: In this paper, a general study of when the director fields can be oriented, described in terms of the topology of the domain filled by the liquid crystal, the boundary data and the rate of blow-up of possible singularities, is presented.
Abstract: Uniaxial nematic liquid crystals are often modeled using the Oseen-Frank theory, in which the mean orientation of the rod-like molecules is described through a unit vector field n. This theory has the apparent drawback that it does not respect the head-to-tail symmetry in which n should be equivalent ton; that is, instead of n taking values in the unit sphere S 2 , it should take values in the sphere with opposite points identified, i.e., in the real projective plane RP 2 . The Landau-de Gennes theory respects this symmetry by working with the tensor Q ¼s (nn � 1/3Id). In the case of a non-zero constant scalar order parameter s the Landau- de Gennes theory is equivalent to that of Oseen-Frank when the director field is orientable. We report on a general study of when the director fields can be oriented, described in terms of the topology of the domain filled by the liquid crystal, the boundary data and the rate of blow-up of possible singularities. We also analyze the circum- stances in which the non-orientable configurations are energetically favoured over the orientable ones.

Journal ArticleDOI
TL;DR: In this paper, the influence of LED backlight on the color performance, electro-optic characteristics of the LCD TVs, and color-sequential LCDs is emphasized, and the LED light source as a 2D adaptive dimming backlight not only enhances the viewing angle but also lowers the power consumption.
Abstract: Recent advances of LED-lit LCD TVs are reviewed. The influence of LED backlight on the color performance, electro-optic characteristics of the LCD TVs, and color-sequential LCDs are emphasized. The LED backlit LCDs not only exhibits a wider color gamut but also has a ∼ 1.3–2.5X smaller color shift than that of CCFL-BLU especially when there are no color filters used. Wide view angle of higher than 100:1 within the 85° viewing cone can be guaranteed with the optimal film compensation schemes. The LED light source as a 2D adaptive dimming backlight not only enhances the viewing angle but also lowers the power consumption. A thin twisted-nematic cell filled with a high birefringence exhibits a response time less than 2 ms, which is attractive for color sequential display using RGB LEDs.

Journal ArticleDOI
TL;DR: In this paper, the effect of nanotubes doping on spectral and photorefractive properties of conjugated organic systems based on polyimide has been studied and shown that these materials could be used as new reversible holographic recording elements, new optical limiting systems, as well as new high-speed switchers.
Abstract: The fullerene- and nanotubes-doping effect on spectral and photorefractive properties of conjugated organic systems based on polyimide have been studied. A fullerene introduction in these materials has been used due to high electron affinity of fullerenes that allows the intermolecular donor-acceptor interaction to be reinforced. The nanotubes doping has been made due to a large increase in photoconductivity of the new composites. Drastic increase in delta n has been observed under condition of nanoobjects introduction. The data presented in the current study testified that these materials could be used as new reversible holographic recording elements, new optical limiting systems, as well as new high-speed switchers.

Journal ArticleDOI
TL;DR: In this paper, a hole-transporting material, 9,9′-diphenyl-9H, 9′H-3, 3, 3′-bicarbazole(P-Cvz-2), 9, 9''-dipsyl-6.
Abstract: We synthesized new hole-transporting material, 9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-2), 9,9′-diphenyl-6-(9-phenyl-9H-carbazol-3-yl)-9H,9′H-3,3′-bicarbazole(P-Cvz-3), 6-(9,9′-diphenyl-9H,9′H-3,3′-bicarbazol-6-yl)-9,9′-diphenyl-9H,9′H-3,3′-bicarbazole(P-Cvz-4A) and 9-phenyl-6-(9-phenyl-9H-3,9′-bicarbazol-6-yl)-9H-3,9′-bicarbazole(P-Cvz-4B). EL luminance efficiencies of P-Cvz-2, P-Cvz-3, P-Cvz-4A and P-Cvz-4B devices were found to be 5.24, 5.64, 4.86 and 4.94 cd/A at 50 mA/cm2, respectively, when synthesized materials are using as a HTL material. The luminance efficiency of P-Cvz-3 is 20% higher than that of NPB, a commercialized HTL material used as a reference in this study.

Journal ArticleDOI
TL;DR: In this paper, the intrinsic alignment of the droplets induced by the structural field is similar to the alignment induced by an external field of 6E7 V/m, i.e., the droplet directors are strongly trapped along the direction of the grating vector.
Abstract: Electric field-induced reorientation of liquid crystal droplets in holographic polymer-dispersed liquid crystal (HPDLC) transmission gratings was investigated. In-plane reorientation of the droplet directors was attained by the use of interdigitated ITO electrodes. Samples with different angles between the directions of the grating vector and the electrodes were analyzed. The results show that intrinsic alignment of the droplets induced by the structural field is similar to the alignment induced by an external field of 6E7 V/m, i.e., the droplet directors are strongly trapped along the direction of the grating vector.

Journal ArticleDOI
TL;DR: In this paper, phase diagrams of the binary mixtures of the title compounds were constructed to investigate the effect of different polar substituents, on the pyridine-based derivatives, as well as the alkoxy-chain length on the acids, and on the extent and stability of the supramolecular liquid crystal phases induced by intermolecular hydrogen bonding.
Abstract: Phase diagrams of the binary mixtures of the title compounds were constructed to investigate the effect of different polar substituents, on the pyridine-based derivatives, as well as the alkoxy-chain length, on the acids, on the extent and stability of the supramolecular liquid crystal phases induced by intermolecular hydrogen bonding. None of the newly prepared pyridine-based derivatives is mesomorphic, but the hydrogen-bonded complexes are. The mixtures prepared were characterized for their mesophase behavior by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Five pyridine-based derivatives (I a-e), with molecular formula X-C6H4COOC6H4-N=N-C5H4N, were prepared that differ from each other by the substituent X. The latter varies between CH3O, CH3, H, Br, and NO2. Four 4-alkoxybenzoic acids (CnH2n+1OC6H4COOH, II 10–II 18) were used; the number of carbons (n) of their alkoxy groups varies between 10, 12, 14, and 18. Smectic C mesophase is induced in most of the binary mixtures ...

Journal ArticleDOI
TL;DR: In this article, phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 ) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.).
Abstract: Phototuning of Bragg reflection bandgap from green to blue and from red to green wavelengths was induced with a green (λ = 532 nm) laser beam in a cholesteric liquid crystal based on highly sensitive azobenzene nematic BEAM 1005 (BEAM Co.) and UV transparent non-photoisomerizable optically active dopant ZLI-6248 (R-2011) (Merck Ltd.). Optical switching between reflected and transmitted beams, as well as nonlinear transmission and reflection due to Bragg reflection band shift are studied in detail.

Journal ArticleDOI
TL;DR: In this article, the results of the studies of the orientational optical nonlinearity of a nematic host doped with high-molar-mass compounds of different molecular architecture such as a comb-like polymer and a dendrimer containing azobenzene chromophores are presented.
Abstract: The results of the studies of the orientational optical nonlinearity of a nematic host doped with high-molar-mass compounds of different molecular architecture such as a comb-like polymer and a dendrimer containing azobenzene chromophores are presented. The nonlinearity induced by these compounds was found to be higher than that induced by the low-molar-mass dyes similar in structure to the light-absorbing constituents of the polymer and dendrimer. Possible reasons for the nonlinearity enhancement for macromolecular dopants are discussed.

Journal ArticleDOI
TL;DR: In this article, mesomorphic and physical properties of several fluorinated NCS terphenyl single compounds and mixtures based solely on laterally fluorinated aromatic rigid core structures are reported.
Abstract: High birefringence (Δn > 0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time. In this paper, we report the mesomorphic and physical properties of several fluorinated NCS terphenyl single compounds and mixtures based solely on laterally fluorinated aromatic rigid core structures. The single compounds have Δn ∼ 0.35 in the visible spectral region and relatively low viscosity. In terms of applications, these compounds can be used as a dopant for enhancing the figure-of-merit of commercial mixtures for display applications. Or we can formulate high birefringence eutectic mixtures using solely NCS terphenyl compounds for near IR laser beam steering applications.

Journal ArticleDOI
TL;DR: In this article, a pixel structure of viewing angle switchable liquid crystal display (LCD) associated with fringe-field switching (FFS) mode using one panel is proposed.
Abstract: We propose a pixel structure of viewing angle switchable liquid crystal display (LCD) associated with fringe-field switching (FFS) mode using one panel. In the device, one pixel is composed of main- and sub-pixel, in which the former has a role of image expression using the FFS mode and the latter has a role of viewing angle switching using the electrically controllable birefringence (ECB) mode. Consequently, before applying voltage to the sub-pixel, the device shows wide viewing angle, however, when the proper voltage is applied to the sub pixel, the displayed image is blocked in an oblique viewing angle.

Journal ArticleDOI
TL;DR: In this article, a review focuses on the covalent modification of the surface of nanotubes by means of 1,3-dipolar cycloaddition of azomethine ylides and some recent examples illustrate the applications of the final products.
Abstract: Applications of carbon nanotubes in different fields, ranging from nanomedicine to photophysics, have emerged since the discovery of this new carbon structure. Functionalization of the nanotubes enhances solubility, facilitates handling as well as provides a way to introduce new molecular entities that will generate interesting properties. This review focuses on the covalent modification of the surface of nanotubes by means of 1,3-dipolar cycloaddition of azomethine ylides and some recent examples will illustrate the applications of the final products.

Journal ArticleDOI
TL;DR: In this article, it was shown that the ultrasonic dispersion of TEG in the epoxy matrix leads to a shift of the percolation transition in the electrical conductivity to higher values of the graphite content and decreases the thermal conductivity of these CMs.
Abstract: Thermal and electrical conductivities in composites (CMs) based on various types of polymer matrix – epoxy resin (epoxy) and polyethylene oxide (PEO) have been investigated in the temperature range 150–300 K. A few types of carbon materials have been used as a filler in CMs: thermoexfoliated graphite (TEG) (TEG content was 0.5–10 wt.%), TEG dispersed in an ultrasonic disperser (nano-TEG) (content – 1–2 wt.%),and multiwalled carbon nanotubes (MWCNTs) (content – 1–10 wt.%). It was shown that the ultrasonic dispersion of TEG in the epoxy matrix leads to a shift of the percolation transition in the electrical conductivity to higher values of the graphite content and decreases the thermal conductivity of these CMs. This occurs due to the break down of the worm-like structure of TEG particles, i.e., the already formed fragments of TEG clusters. It is revealed also that the use of epoxy as a polymer matrix and a nondispersed thermoexfoliated graphite as a filler gives the greatest values of the thermal and elect...

Journal ArticleDOI
TL;DR: In this article, surface relief gratings were inscribed on amorphous azobenzene polymer thin films using a holographic pattern of circularly polarized light at wavelength equal to 514nm in a vacuum chamber to avoid the hot air turbulence.
Abstract: The temperature dependence of surface relief grating formation was studied using continuous and pulse like exposure. Surface relief gratings were inscribed on amorphous azobenzene polymer thin films using a holographic pattern of circularly polarized light at wavelength equal to 514 nm in a vacuum chamber to avoid the hot air turbulence. The efficiency of the surface relief grating formation was probed using a He-Ne laser of wavelength 633 nm by monitoring the first order diffraction peak (I1) as well as the specularly reflected intensity (Is). Under continuous exposure permanent grating formation was observed up to a temperature of about 100°C only. The same was found under pulse like exposure but grating still exists as long as the actinic light is on. Above 100°C it relaxes entirely after switching the light off. This elastic component disappears at about 115°C, i.e., close to the glass transition temperature. Our findings can be interpreted by the competition between light-induced ordering of azobenze...

Journal ArticleDOI
TL;DR: In this article, the results of gelatin-based electrolyte were characterized by impedance spectroscopy, X-ray diffraction and thermal analysis, and the ionic conductivity results obtained for these solid polymeric electrolytes were 1.5 × 10−5 S/cm and 4.9× 10−4 S/ cm at room temperature and 80°C, respectively.
Abstract: Natural polymers are particularly interesting due to their richness in nature, very low cost and principally biodegradation properties. For these reasons different solid polymeric electrolytes (SPE) have been obtained using cellulose derivatives, starch, chitosan and rubber. This work presents the results of gelatin-based electrolyte, which were characterized by impedance spectroscopy, X-ray diffraction and thermal analysis. The ionic conductivity results obtained for these SPEs were 1.5 × 10−5 S/cm and 4.9 × 10−4 S/cm at room temperature and 80°C, respectively. Temperature-dependence ionic conductivity measurements were taken to analyze the mechanism of ionic conduction in polymer electrolytes. Thermal analysis using differential scanning calorimetry (DSC) was performed in order to observe the change in transition temperature caused by the addition of salt to the electrolyte. Good conductivity results combined with transparency and good adhesion to the electrodes have shown that gelatin-based SPEs are ve...

Journal ArticleDOI
TL;DR: In this paper, the dispersion of the cubic nonlinear optical properties of organic and organometallic nonlinear absorbers was studied and it was shown that a multitude of excited states may contribute to the resonances seen in the real and imaginary part of the complex hyperpolarizability.
Abstract: We have studied dispersion of the cubic nonlinear optical properties of organic and organometallic nonlinear absorbers. The results indicate that a multitude of excited states may be contributing to the resonances seen in the real and imaginary part of the complex hyperpolarizability. Attempts to understand the relation between the real and imaginary part of the hyperpolarizability in terms of a Kramers-Kronig transform are undertaken.

Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of recent results obtained in nano-dispersed nonlinear neat organic liquids and liquid crystals and confirm the enhancement of nonlinear absorption in gold nano-spheres doped neat nonlinear liquids and extension of the bandwidth of efficient all-optical switching operation for visible-near infrared lasers in time scales ranging from sub-picoseconds through nanosecond and microseconds and longer.
Abstract: We present an overview of recent results obtained in nano-dispersed nonlinear neat organic liquids and liquid crystals. Experimental observations confirm the enhancement of nonlinear absorption in gold nano-spheres doped neat nonlinear liquids and extension of the bandwidth of efficient all-optical switching operation for visible-near infrared lasers in time scales ranging from sub-picoseconds through nanoseconds and microseconds and longer. Similar nano-particulate doped liquid crystal films also exhibit efficient all-optical switching capabilities for microseconds – cw lasers. Meta-materials fabricated with core-shell nano-spheres dispersed nematic liquid crystals show effective refractive indices that are tunable from negative through zero to positive values.

Journal ArticleDOI
TL;DR: In this paper, a comparative study of hole-mobility in N,N′-diphenyl and 4,4′ diamine (TPD) using three independent measurement techniques is presented.
Abstract: A comparative study of hole-mobility in N,N′-diphenyl-N,N′-di(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) using three independent measurement techniques is presented. Time-of-flight (TOF), steady-state space charge-limited current (SCLC) experiments are carried-out in neat films of TPD, sandwiched between electrodes with different work functions. Organic field-effect transistors (OFET) are fabricated from TPD thin films and their electrical properties characterized. The comparative results show that all-electrical measurements that involve carrier injection from a metal electrode into the organic film yield effective mobility values that are one order of magnitude lower than those obtained from time-of-flight experiments in which carriers are created in the film optically. Similarly, SCLC and TOF experiments were used to measure electron-mobility in a discoid organic compound 2,3,8,9,14,15-hexakis-dodecylsulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA-(SC12H25)6).