Light emitting diodes containing Langmuir-Blodgett films of copolymer of a poly(p-phenylene-vinylene) derivative and poly(octaneoxide)

The properties of Langmuir and Langmuir-Blodgett (LB) films from a block copolymer with polyethylene oxide and phenylene-vinylene moieties are reported. The LB films were successfully transferred onto several types of substrates, with sufficient quality to allow for evaporation of a metallic electrode on top of the LB films to produce polymer light emitting diodes (PLEDs). The photoluminescence and electroluminescence spectra of the LB film and device were similar, featuring an emission at ca. 475 nm, from which we could infer that the emission mechanisms are essentially the same as in poly(p-phenylene) derivatives. Analogously to other PLEDs the current versus voltage characteristics of the LB-based device could be explained with the Arkhipov model according to which charge transport occurs among localized sites. The implications for nanotechnology of the level of control that may be achieved with LB devices will also be discussed.

Electrical transport properties of doped poly (p-phenylene)

An experimental study of the temperature dependent dc electrical conductivity of doped poly (p-phenylene) in the range of 50-300 K has been presented. The results have been analyzed in the framework of some hopping models. We have observed that hopping models are not consistent with the temperature dependence of the conductivity data over the entire temperature range of measurement. We find that the logarithmic conductivity is proportional to T-beta, wherethe exponent beta is independent of temperature. It is shown that the most probable transport process in this material for the entire range of temperature is due to multiphonon-assisted hopping of the charge carriers that interact weakly with phonons. The parameters obtained from the fits of the experimental data to this model appear reasonable.

Spectroscopic and thermal characterization in poly(p-phenylene vinylene)/sol-gel silica sample

The absorption and luminescence spectra for the poly(p-phenylene vinylene)/sol-gel silica with different thermal treatments were measured. A considerable increase in the luminescence was observed for the polymer introduced into SiO2 matrix with thermal treatment at 120 degreesC. The thermal diffusivity of these samples was measured using the thermal lens technique, and the obtained value 3.3 x 10(-5) cm(2)/s (sample treated at 37 degreesC) is practically independent of the thermal treatment (37-150 degreesC). (C) 2003 Elsevier B.V. All rights reserved.

Structure control of poly(p-phenylene vinylene) in layer-by-layer films by deposition on a charged poly(o-methoxyaniline) cushion

In this paper, we demonstrate that the intrinsic electric field created by a poly(o-methoxyaniline) (POMA) cushion layer hinders the changes in molecular conformation of poly(p-phenylenevinylene) (PPV) in layer-by-layer with dodecylbenzene sulfonic acid (DBS). This was modeled with density functional theory (DFT) calculations where an energy barrier hampered molecular movements of PPV segments when they were subjected to an electric field comparable to that caused by a charged POMA layer. With restricted changes in molecular conformation, the PPV film exhibited Franck-Condon transitions and the photoexcitation spectra resembled the absorption spectra, in contrast to PPV/DBS films deposited directly on glass, with no POMA cushion. Other effects from the POMA cushion were the reduced number of structural defects, confirmed with Raman spectroscopy, and an enhanced PPV emission at high temperatures (300 K) in comparison with the films on bare glass. The positive effects from the POMA cushion may be exploited for enhanced opto-electronic devices, especially as the intrinsic electric field may assist in separating photoexcited electron-hole pairs in photovoltaic devices. © 2013 American Institute of Physics.

Effect of a Polymeric Protective Coating on Optical and Electrical Properties of Poly(p-phenylene vinylene) Derivatives

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efficiency of extrinsic and intrinsic charge-carrier photogeneration processes obtained from the steady-state photocurrent action spectra of poly(p-phenylene vinylene) derivatives

The efficiency of the charge-carrier photogeneration processes in poly(2,5-bis(3',7'-dimethyl-octyloxy)-1,4-phenylene vinylene) (OC(1)OC10-PPV) has been analyzed by the spectral response of the photocurrent of devices in ITO/polymer/Al structures. The symbatic response of the photocurrent action spectra of the OC1OC10-PPV devices, obtained for light-excitation through the ITO electrode and for forward bias, has been fitted using a phenomenological model which considers that the predominant transport mechanism under external applied electric field is the drift of photogenerated charge-carriers, neglecting charge-carrier diffusion. The proposed model takes into account that charge-carrier photogeneration occurs via intermediate stages of bounded pairs (excitonic states), followed by dissociation processes. Such processes result in two different contributions to the photoconductivity: The first one, associated to direct creation of unbound polaron pairs due to intrinsic photoionization; and the second one is associated to secondary processes like extrinsic photoinjection at the metallic electrodes. The results obtained from the model have shown that the intrinsic component of the photoconductivity at higher excitation energies has a considerably higher efficiency than the extrinsic one, suggesting a dependence on the photon energy for the efficiency of the photogeneration process.

Effect of a polymeric protective coating on optical and electrical properties of poly (p-phenylene vinylene) derivatives

The resistance to photodegradation of poly [(2-methoxy-5-n-hexyloxy)-p-phenylene vinylene] (OC1OC6-PPV) films was significantly enhanced by the use of poly(vinyl alcohol) 99% hydrolyzed as protective coating. The deposition of poly(vinyl alcohol) onto OC1OC6-PPV films did not affect the absorption and the emission spectra of the luminescent polymer. The protected film showed 5% drop on the absorbance at 500nm after 270 hours of light exposure while the unprotected film completely degraded in the same conditions. The conductivity of the protected film remained stable (around 7 × 10-10 S/m) while the value for the unprotected one dropped around two orders of magnitude after 100 hours of light exposure.

Determination of density of states in PPS from space-charge-limited current measurements

Space-charge-limited currents measurements have been carried out on undoped amorphous poly p-phenylene sulfide. The scaling law is checked for different samples with varying thickness, and J-V data analyzed. The position of the quasi-Fermi level and the density of states was obtained.

Pi-konjugierte Plasmapolymere als organische Halbleiter durch vorstrukturierte single-source-Precursoren

Die vorliegende Arbeit behandelt die Entwicklung einer neuartigen Synthesestrategie von π-konjugierten Plasmapolymeren durch die Anwendung von vorstrukturierten aromatischen Precursoren und gepulsten Niederdruckplasmen. Es gelang erstmals die strukturtreue Synthese von π-konjugierten organischen Plasmapolymeren mit dem vollkommenen Erhalt der aromatischen Funktionalität und der selektiven para-Verknüpfung aromatischer Einheiten durch geeignete Heteroatome. Hierbei kamen 1,4-Dithiophenol zur Synthese von Plasmapoly(p-phenylensulfid) und 4-Iodanilin zur Synthese von Plasmapolyanilin zur Anwendung. Die mit hoher Präzision abgeschiedenen Filme konnten sowohl postsynthetisch als auch in situ p-dotiert werden. Die chemischen Strukturen sowie deren physikalisch-chemischen Eigenschaften konnten vor allem mittels Röntgenphotoelektronen-, UV-VIS-NIR-, IR-, NMR-, ESR- und Impedanz-Spektroskopie aufgeklärt werden. Die synthetisierten dotierten Plasmapolymere zeigten eindeutig ohmsche Leistungsmechanismen, teilweise mit einer Leitfähigkeitserhöhung von bis zu 8 Dekaden gegenüber dem undotierten konventionellen Polymer.

Solid-state sensory properties of Calix-Poly(Phenylene Ethynylene)s toward nitroaromatic explosives

This study is primarily focused in establishing the solid-state sensory abilities of several luminescent polymeric calix[4]arene-based materials toward selected nitroaromatic compounds (NACs), creating the foundations for their future application as high performance materials for detection of high explosives. The phenylene ethynylene-type polymers possessing bis-calix[4]arene scaffolds in their core were designed to take advantage of the known recognition abilities of calixarene compounds toward neutral guests, particularly in solid-state, therefore providing enhanced sensitivity and selectivity in the sensing of a given analyte. It was found that all the calix[4]arene-poly(para-phenylene ethynylene)s here reported displayed high sensitivities toward the detection of nitrobenzene, 2,4-dinitrotoluene and 2,4,6-trinitrotoluene (TNT). Particularly effective and significant was the response of the films (25-60 nm of thickness) upon exposure to TNT vapor (10 ppb): over 50% of fluorescence quenching was achieved in only 10 s. In contrast, a model polymer lacking the calixarene units showed only reduced quenching activity for the same set of analytes, clearly highlighting the relevance of the macrocyclics in promoting the signaling of the transduction event. The films exhibited high photostability (less than 0.5% loss of fluorescence intensity up to 15 min of continuous irradiation) and the fluorescence quenching sensitivity could be fully recovered after exposure of the quenched films to saturated vapors of hydrazine (the initial fluorescence intensities were usually recovered within 2-5 min of exposure to hydrazine).

Lead sulfide nanocrystal: conducting polymer solar cells

In this paper, we report photovoltaic devices fabricated from lead sulfide nanocrystals and the conducting polymer poly(2-methoxy-5-(2'-ethyl-hexyloxy)-p-phenylene vinylene). This composite material was produced via a new single-pot synthesis which solves many of the issues associated with existing methods. Our devices have white light power conversion efficiencies under AM 1.5 illumination of 0.7% and single wavelength conversion efficiencies of 1.1%. Additionally, they exhibit remarkably good ideality factors (n = 1.15). Our measurements show that these composites have significant potential as soft optoelectronic materials.

Thickness and Annealing Temperature Effects on the Optical Properties and Surface Morphology of Layer-by-Layer Poly(p-phenyline vinylene) plus Dodecylbenzenesulfonate Films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 degrees C had a dichroic ratio delta = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with delta = 1.0 for a 75-layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self-covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 206-213, 2011

Efeito da degradação ambiental nas propriedades de cisalhamento de compósitos PPS/fibra de carbono

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The effect of the ocean water immersion and UV ageing on the dynamic mechanical properties of the PPS/glass fiber composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avaliação dos parâmetros de soldagem para compósitos de PPS/fibras contínuas com aplicações aeronáuticas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)