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.

Correlations between Conjugation Length, Macromolecular Dynamics, and Photophysics of Phenylene-Vinylene/Aliphatic Multiblock Copolymers

This work reports a detailed spectroscopy study of a series of multiblock conjugated nonconjugated copolymers built by p-phenylene vinylene type units (PV) and octamethylene spacers, namely, poly(1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene) (LaPPS18). The relative proportions of the PV and aliphatic segments were estimated on the basis of solid-state NMR and Raman spectroscopy. The overall structure was characterized by wide angle X-ray diffraction; H-1 wide-line dipolar chemical shift correlation (DIPSHIFT), and centerband-only detection of exchange (CODEX) NMR data, that together with glass transition temperatures allowed us to identify the groups involved in the molecular dynamics. These different structural properties were used to explain the photoluminescence properties in terms of peak position and spectral profile

Determination of carrier mobility in MEH-PPV thin-films by stationary and transient current techniques

Charge transport and shelf-degradation of MEH-PPV thin-films were investigated through stationary (e.g. current versus voltage - JxV) and transient (e.g. Time-of-Flight - ToF, Dark-Injection Space-Charge-Limited Current - DI-SCLC, Charge Extraction by Linearly Increasing Voltage - CELN) current techniques. Charge carrier mobility in nanometric films was best characterized through JxV and DI-SCLC. It approaches 10(-6) cm(2)Ns under a SCLC regime with deep traps for light-emitting diode applications. ToF measurements performed on micrometric layers (i.e. - 3 mu m) confirmed studies in 100 nm-thick films as deposited in OLEDs. All results were comparable to a similar poly(para-phenylene vinylene) derivative, MDMO-PPV. Electrical properties extracted from thin-film transistors demonstrated mobility dependence on carrier concentration in the channel (similar to 10(-7)-10(-4) cm(2)/Vs). At low accumulated charge levels and reduced free carrier concentration, a perfect agreement to the previously cited techniques was observed. Degradation was verified through mobility reduction and changes in trap distribution of states. (C) 2011 Elsevier B.V. All rights reserved.

Electroluminescence of phenylene-vinylene random copolymers with different conjugation lengths

PPV random derivates were synthesized and characterized. Polymer light emitting diodes (PLEDs) were assembled using the random copolymers as emissive layer and showed EL in the blue-green region in function of the method of preparation. The increase in the average conjugation degree in the polymer chain led to the reduction of the turn-on voltage of the device. The addition of Alq3 as ETL increased tenfold the luminescence efficiency. (C) 2009 Elsevier B.V. All rights reserved.

Influence of polyaniline and phthalocyanine hole-transport layers on the electrical performance of light-emitting diodes using MEH-PPV as emissive material

The influence of layer-by-layer films of polyaniline and Ni-tetrasulfonated phthalocyanine (PANI/Ni-TS-Pc) on the electrical performance of polymeric light-emitting diodes (PLED) made from (poly[2-methoxy-5-(2`-ethyl-hexyloxy)-1,4-phenylene vinylene]) (MEH-PPV) is investigated by using current versus voltage measurements and impedance spectroscopy. The PLED is composed by a thin layer of MEH-PPV sandwiched between indium tin oxide (ITO) and aluminum electrodes, resulting in the device structure ITO/(PANI/Ni-TS-Pc)(n)/MEH-PPV/Al, where n stands for the number of PANI/Ni-TS-Pc bilayers. The deposition of PANI/Ni-TS-Pc leads to a decrease in the driving voltage of the PLEDs, which reaches a minimum when n = 5 bilayers. In addition, impedance spectroscopy data reveal that the PLED impedance decreases as more PANI/Ni-TS-Pc bilayers are deposited. The PLED structure is further described by an equivalent circuit composed by two R-C combinations, one for the bulk and other for the interface components, in series with a resistance originated in the ITO contact. From the impedance curves, the values for each circuit element is determined and it is found that both, bulk and interface resistances are decreased upon PANI/Ni-TS-Pc deposition. The results indicate that PANI/NiTS-Pc films reduce the contact resistance at ITO/MEH-PPV interface, and for that reason improve the hole-injection within the PLED structure. (c) 2007 Elsevier B.V. All rights reserved.

Polymer Light Emitting Diode Using PFT-Poly(9,9 `-n-dihexil-2,7-fluorenodiilvinylene-alt-2,5thiophene)

The development of new electroluminescence polymers for specific colour tuning in Polymer Light Emitting Devices (PLEDs) is currently one of the most important fields for organic electronics. This work reports a synthesis of a new electroluminescent polymer and the concomitant test as PLED emissive layer. The polymer, synthesised from fluorene, is poly(9,9`-n-dihexil-2,7-fluorenodiilvinylene-alt-2,5thiophene) or PFT The luminescence shows large bands with maxima around 480 nm in absorption and 560 nm in emission. The device was made in a three layer structure, with PEDOT:PSS as hole transport layer, PFT as emissive layer and butyl-PBD as electron transport layer. The electroluminescence spectrum shows a strong band peaked at 540 nm. For an applied voltage of 12 Volt, the brightness at normal angle of viewing is near 10 cd/m(2) and the luminous efficiency is of 0.01 lm/W. A discussion about carrier transport and the electroluminescence properties is made.

Biogeochemistry of a deep-sea whale fall: sulfate reduction, sulfide efflux and methanogenesis

Deep-sea whale falls create sulfidic habits Supporting chemoautotrophic communities, but microbial processes underlying the formation Of Such habitats remain poorly evaluated. Microbial degradation processes (sulfate reduction, methanogenesis) and biogeochemical gradients were studied in a whale-fall habitat created by a 30 t whale carcass deployed at 1675 m depth for 6 to 7 yr on the California margin. A variety of measurements were conducted including photomosaicking, microsensor measurements, radio-tracer incubations and geochemical analyses. Sediments were Studied at different distances (0 to 9 in) from the whale fall. Highest microbial activities and steepest vertical geochemical gradients were found within 0.5 m of the whale fall, revealing ex situ sulfate reduction and in vitro methanogenesis rates of up to 717 and 99 mmol m(-2) d(-1), respectively. In sediments containing whale biomass, methanogenesis was equivalent to 20 to 30%, of sulfate reduction. During in vitro sediment studies, sulfide and methane were produced within days to weeks after addition of whale biomass, indicating that chemosynthesis is promoted at early stages of the whale fall. Total sulfide production from sediments within 0.5 m of the whale fall was 2.1 +/- 3 and 1.5 +/- 2.1 mol d(-1) in Years 6 and 7, respectively, of which similar to 200 mmol d(-1) were available as free sulfide. Sulfate reduction in bones was much lower, accounting for a total availability of similar to 10 mmol sulfide d(-1). Over periods of at least 7 yr, whale falls can create sulfidic conditions similar to other chemosynthetic habitats Such as cold seeps and hydrothermal vents.

Production and characterization of poly-(3-hydroxybutyrate) from recombinant Escherichia coli grown on cheap renewable carbon substrates

Although the biopolymer poly-(3-hydroxybutyrate), P[3HB], presents physicochemical properties that make it an alternative material to conventional plastics, its biotechnological production is quite expensive. As carbon substrates contribute greatly to P[3HB] production cost, the utilization of a cheaper carbon substrate and less demanding micro-organisms should decrease its cost. In the present study a 23 factorial experimental design was applied, aiming to evaluate the effects of using hydrolysed corn starch (HCS) and soybean oil (SBO) as carbon substrates, and cheese whey (CW) supplementation in the mineral medium (MM) on the responses, cell dried weigh (DCW), percentage P[3HB] and mass P[3HB] by recombinant Escherichia coli strains JM101 and DH10B, containing the P[3HB] synthase genes from Cupriavidus necator (ex-Ralstonia eutropha). The analysis of effects indicated that the substrates and the supplement and their interactions had positive effect on CDW. Statistically generated equations showed that, at the highest concentrations of HCS, SO and CW, theoretically it should be possible to produce about 2 g L(1) DCW, accumulating 50% P[3HB], in both strains. To complement this study, the strain that presented the best results was cultivated in MM added to HCS, SBO and CW ( in best composition observed) and complex medium (CM) to compare the obtained P[3HB] in terms of physicochemical parameters. The obtained results showed that the P[3HB] production in MM (1.29 g L(-1)) was approximately 20% lower than in CM (1.63 g L(-1)); however, this difference can be compensated by the lower cost of the MM achieved by the use of cheap renewable carbon sources. Moreover, using differential scanning calorimetry and thermogravimetry analyses, it was observed that the polymer produced in MM was the one which presented physicochemical properties (Tg and Tf) that were more similar to those found in the literature for P[3HB].

Hemocompatibility of poly(epsilon-caprolactone) lipid-core nanocapsules stabilized with polysorbate 80-lecithin and uncoated or coated with chitosan

The hemocompatibility of nanoparticles is of critical importance for their systemic administration as drug delivery systems. Formulations of lipid-core nanocapsules, stabilized with polysorbate 80-lecithin and uncoated or coated with chitosan (LNC and LNC-CS), were prepared and characterized by laser diffraction (D[4,3]: 129 and 134 nm), dynamic light scattering (119 nm and 133 nm), nanoparticle tracking (D50: 124 and 139 nm) and particle mobility (zeta potential: -15.1 mV and + 9.3 mV) analysis. In vitro hemocompatibility studies were carried out with mixtures of nanocapsule suspensions in human blood at 2% and 10% (v/v). The prothrombin time showed no significant change independently of the nanocapsule surface potential or its concentration in plasma. Regarding the activated partial thromboplastin time, both suspensions at 2% (v/v) in plasma did not influence the clotting time. Even though suspensions at 10% (v/v) in plasma decreased the clotting times (p < 0.05), the values were within the normal range. The ability of plasma to activate the coagulation system was maintained after the addition of the formulations. Suspensions at 2% (v/v) in blood showed no significant hemolysis or platelet aggregation. In conclusion, the lipid-core nanocapsules uncoated or coated with chitosan are hemocompatible representing a potential innovative nanotechnological formulation for intravenous administration. (C) 2012 Elsevier B. V. All rights reserved.

Plasmid DNA partitioning and separation using poly(ethylene glycol)/poly(acrylate)/salt aqueous two-phase systems

Phase diagrams of poly(ethylene glycol)/polyacrylate/Na2SO4 systems have been investigated with respect to polymer size and pH. Plasmid DNA from Escherichia coil can depending on pH and polymer molecular weight be directed to a poly(ethylene glycol) or to a polyacrylate-rich phase in an aqueous two-phase system formed by these polymers. Bovine serum albumin (BSA) and E. coil homogenate proteins can be directed opposite to the plasmid partitioning in these systems. Two bioseparation processes have been developed where in the final step the pDNA is partitioned to a salt-rich phase giving a total process yield of 60-70%. In one of them the pDNA is partitioned between the polyacrylate and PEG-phases in order to remove proteins. In a more simplified process the plasmid is partitioned to a PEG-phase and back-extracted into a Na2SO4-rich phase. The novel polyacrylate/PEG system allows a strong change of the partitioning between the phases with relatively small changes in composition or pH. (C) 2012 Elsevier B.V. All rights reserved.

Partitioning and extraction of collagenase from Penicillium aurantiogriseum in poly(ethylene glycol)/phosphate aqueous two-phase system

Purification of collagenase produced by Penicillium aurantiogriseum URM4622 was carried using a PEG/phosphate aqueous two-phase system (ATPS). A 2(3)-full experimental design was used to investigate the influence of PEG molar mass, PEG concentration and phosphate concentration on the selected responses, namely partition coefficient, activity yield and purification factor. The ATPS was composed of PEG (molar mass of 550, 1500 and 4000 g/mol) at concentrations of 15.0, 17.5 and 20.0% (w/w) and phosphate at concentrations of 12.5, 15.0 and 17.5% (w/w). The best results of one-step extraction of collagenase from the fermentation broth (partition coefficient of 1.01, activity yield of 242% and purification factor of 23.5) were obtained at pH 6.0 using 20.0% (w/w) PEG 550 and 17.5% (w/w) phosphate. The results of this preliminary study demonstrate that the selected ATPS is satisfactorily selective for the extraction of such a collagenase. (C) 2012 Elsevier B.V. All rights reserved.

Preparation, characterization and structure of ruthenium phosphine complexes containing non-innocent ligands

Phosphine ruthenate complexes containing the non-innocent ligands 4-chloro-1,2-phenylenediamine (opda-CI) and 3,3',4,4'-tetraamminebiphenyl (diopda) were synthesized and characterized by means of X-ray diffraction, electrochemistry, P-31{H-1} NMR and electronic spectroscopies. Crystals of cis-[RuCl2 (dppb)(bqdi-CI)] complex were isolated as a mixture of two conformational isomers due to different positions of the chlorine atoms of the o-phenylene ligand in relation to the P1 atom of the phosphine moiety. (C) 2011 Elsevier Ltd. All rights reserved.

Understanding the mechanical and biodegradation behaviour of poly(hydroxybutyrate)/rubber blends in relation to their morphology

In this work poly(hydroxybutyrate/poly(vinyl butyral)- co-(vinyl alcohol)-co(vinyl acetate) (or ethylene propylene diene monomer rubber) blends were prepared by conventional processing techniques (extrusion and injection moulding). A droplet type morphology was obtained for P(3HB)/PVB blends whereas P(3HB)/EPDM blends presented some extent of co-continuous morphology. In addition, rubbery domains were much smaller in the case of PVB. These differences in morphology are discussed taking into account solubility parameters and rheological behaviours of each component. For both blends, the increase of elastomer ratio led to a decrease of Young's modulus but an increase in elongation at break and impact strength. The latter increased more in the case of P(3HB)/EPDM blends although the rubbery domains were larger. These results are explained in the light of the glass transition of the rubber and the presence of plasticizer in the case of PVB. The addition of elastomer also resulted in an increase of P(3HB) biodegradation rate, especially in the case of EPDM. It is assumed that, in this case, the size and morphology of the rubbery domains induce a geometrical modification of the erosion front which leads to an increase of the interface between P(3HB) phase and the degradation medium and consequently to an apparently faster biodegradation kinetics of PHB/rubber blends. Copyright (C) 2011 Society of Chemical Industry

Formation and Characterization of Oriented Micro-and Nanofibers Containing Poly (ethylene oxide) and Pectin

Formation of oriented or aligned micro- and nanofibers using biocompatible materials opens the possibility to obtain engineered tissues that can be used in medicine, environmental engineering, security and defense, among other applications. Pectin, a heteropolysaccharide, is a promising material to be incorporated into the fibers because, besides being biocompatible, this material is also biodegradable and bioactive. In this work, the formation of oriented fibers using solutions containing pectin and polyethylene oxide (biocompatible polymers), and chloroform (as the solvent) is investigated. The injection of solution into an intense electric field defined between two parallel electrodes was used to obtain oriented fibers. This novel approach is a modification of the conventional electrospinning process. The presence of pectin in the fibers was confirmed by FTIR analysis. Fibers with diameters of hundreds of nanometers and several centimeters long can be collected. The incorporation of pectin leads to a higher variation of the diameter of the fibers, and a trend to larger fiber diameters. This behavior can be related to the presence of pectin clusters in the fibers. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.057203jes] All rights reserved.