Non ohmic gigahertz conductivity in pressed pellets of ClO4 doped poly(3-methylthiophene)

ESR measurements In pressed pellets of doped Poly(3-Methylthiophene)(P3MT) were performed at 10 K and 50 K after cooling the system slowly from room temperature to 110 K, quenching to 77 K and then to 10 K. ESR line asymmetry (A/B) as a function of microwave power was observed and 9.4 GHz conductivity was obtained from Dyson's theory. The data is discussed in terms of Charge-Density Wave (CDW) depinning. At 50 K the threshold electric field is estimated to be less than 1 V/cm. At 10 K a subtle pinning of the CDW was observed around 15 mW.

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.

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.

Preparation and characterization of poly(vinyl butyral)-polyaniline-montmorillonite nanocomposites

Poly(vinyl butyral)-polyaniline-sodium montmorillonite nanocomposites were prepared via polymerization of aniline between clay mineral platelets at two different pH levels (2.0 and 5.0), followed by dispersion of the polyaniline-sodium montmorillonite nanocomposite in a poly(vinyl butyral) solution. A comparison was made of the effect of the pH levels and the polyaniline-sodium montmorillonite nanocomposite precursor on the final structures of the poly(vinyl butyral) nanocomposites and their electrical conductivities. X-ray diffraction patterns revealed the formation of nanocomposites at both pH levels. UV-Vis spectra indicated that the polyaniline formed at both pH levels was conductive, with the UV-Vis spectra presenting a band at 420 nm corresponding to the polaronic form and the beginning of a new band at 600 nm indicating the presence of polaronic segments. FTIR spectra revealed the peaks of the groups present in polyaniline and poly(vinyl butyral) nanocomposites. The electrical conductivities of the polyaniline and poly(vinyl butyral) nanocomposites prepared at pH 2.0 were lower than those of the same nanocomposites prepared at pH 5.0, probably due to the lower formation of polyaniline chains in a more acidic dispersion and to the final configuration of polyaniline in the nanocomposites.

Is the poly (methylene blue)-modified glassy carbon electrode an adequate electrode for the simple detection of thiols and amino acid-based molecules?

This paper describes the preparation, characterization, and use of poly (methylene blue) (PMB)-modified glassy carbon electrodes (GCE) (GCE-PMB) in the detection of the thiols L-cysteine (L-CySH) and N-acetyl cysteine (Acy), and the herbicide glyphosate (GLYP) in pH 5.3 aqueous solution. The polymer film prepared by electropolymerization showed different characteristics such as robustness, stability, and redox properties satisfactorily. The surface coverage concentration (Gamma) of PMB was found to be 7.90 x 10(-9) - mol cm(-2). Moreover, we observed strong adhesion of the polymer film to the electrode surface. The results using GCE-PMB as a sensor indicated that this modified electrode exhibited electrocatalytic activity toward the detection of thiols and glyphosate in 0.1 mol L-1 KO (pH 5.3). Meanwhile, strong adsorption of the analytes on the GCE-PMB electrodes was also observed. Otherwise, using a low concentration (1 x 10(-4) mol L-1) of L-cysteine and N-acetyl cysteine and 8.9 x 10(-6) mol L-1 of glyphosate, separately, it was possible to observe a well-defined electrochemical response, thus providing an opportunity to further understand the applicability of PMB as a sensor for amino acid-based molecules. (C) 2012 Elsevier B.V. All rights reserved.

Influence of Molecular Dynamics on the Dielectric Properties of Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) -Based Devices

This paper uses Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) techniques to study the molecular relaxations and phase transitions in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), which has been extensively studied as the active thin film in organic devices. Besides the identification of the glass transition, beta relaxation and crystal-to-crystal phase transition, we correlate such phenomena with dielectric and transport mechanisms in diodes with F8BT as the active layer. The beta relaxation has been assigned to a transition at about 210 K measured by H-1 and C-13 solid state NMR, and can be attributed to local motions in the side chains. The glass transition has been detected by DSC and H-1 NMR. Dielectric spectroscopy (DS) carried out at low frequencies on diodes made from F8BT show two peaks which are coincident with the above transitions. This allowed us to correlate the electrical changes in the film with the onset of specific molecular motions. In addition, DS indicates a third peak related with a crystal-to-crystal phase transition. Finally, these transitions were correlated with changes in the carrier mobility recorded in thin films and published recently.

The Influence of Osteoblast Differentiation Stage on Bone Formation in Autogenously Implanted Cell-Based Poly(Lactide-Co-Glycolide) and Calcium Phosphate Constructs

We tested the hypothesis that the osteoblast differentiation status of bone marrow stem cells (BMSCs) combined with a three-dimensional (3D) structure modulates bone formation when autogenously implanted. Rat BMSCs were aspirated, expanded, and seeded into a 3D composite of poly(lactide-co-glycolide) and calcium phosphate (PLGA/CaP) to produce a hybrid biomaterial. Calvarial defects were implanted with (1) scaffold without cells (SC/NC), (2) scaffold and BMSCs (SC + BMSC), (3) scaffold and osteoblasts differentiated for 7 days (SC + OB7), and (4) for 14 days (SC + OB14). After 4 weeks, there was more bone formation in groups combining scaffold and cells, SC + BMSC and SC + OB7. A nonsignificant higher amount of bone formation was observed on SC + OB14 compared with SC/NC. Additionally, more blood vessels were counted within all hybrid biomaterials, without differences among them, than into SC/NC. These findings provide evidences that the cell differentiation status affects in vivo bone formation in autogenously implanted cell-based constructs. Undifferentiated BMSCs or osteoblasts in early stage of differentiation combined with PLGA/CaP scaffold favored bone formation compared with plain scaffold and that one associated with more mature osteoblasts.

Molecular organization and doping in poly(2-methoxyaniline)/Ni(dmit)(2) films obtained with the Langmuir-Blodgett technique

The control of the properties of materials at the molecular level is pursued for many applications, especially those associated with nanostructures. In this paper, we show that the coordination compound [Ni(dmit)(2)], where (dmit) is the 1,3-dithiole-2-thione-4,5-dithiolate ligand, can induce doping of poly(2-methoxyaniline) (POMA) in molecularly ordered Langmuir and Langmuir-Blodgett (LB) films. Doping was associated with interactions between the components and the compression of the Langmuir film at the air-water interface, according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Taking these results together with in situ UV-Vis absorption measurements, we could identify the molecular groups involved in the interaction, including the way they were reoriented upon film compression. The Langmuir films were sufficiently stable to be transferred as Y-type LB films, while the hybrid POMA/[Ni(dmit)(2)] films remain doped in the solid state. As expected, the molecular charges affected the film morphology, as observed from combined atomic and electric force microscopy measurements. In summary, with adequate spectroscopy and microscopy tools we characterized molecular-level interactions, which may allow one to design molecular electronic devices with controlled electrical properties.

Regioregular improvement on the oxidative polymerization of poly-3-octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat-to-tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl3 is a one-pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl3 addition rate and reaction temperature, poly-3-octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat-to-tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Evaluation of immobilized lipases on poly-hydroxybutyrate beads to catalyze biodiesel synthesis

Five microbial lipase preparations from several sources were immobilized by hydrophobic adsorption on small or large poly-hydroxybutyrate (PHB) beads and the effect of the support particle size on the biocatalyst activity was assessed in the hydrolysis of olive oil, esterification of butyric acid with butanol and transesterification of babassu oil (Orbignya sp.) with ethanol. The catalytic activity of the immobilized lipases in both olive oil hydrolysis and biodiesel synthesis was influenced by the particle size of PHB and lipase source. In the esterification reaction such influence was not observed. Geobacillus thermocatenulatus lipase (BTL2) was considered to be inadequate to catalyze biodiesel synthesis, but displayed high esterification activity. Butyl butyrate synthesis catalyzed by BTL2 immobilized on small PHB beads gave the highest yield (approximate to 90 mmol L-1). In biodiesel synthesis, the catalytic activity of the immobilized lipases was significantly increased in comparison to the free lipases. Full conversion of babassu oil into ethyl esters was achieved at 72 h in the presence of Pseudozyma antarctica type B (CALB), Thermomyces lanuginosus lipase (Lipex (R) 100L) immobilized on either small or large PHB beads and Pseudomonas fluorescens (PFL) immobilized on large PHB beads. The latter preparation presented the highest productivity (40.9 mg of ethyl esters mg(-1) immobilized protein h(-1)). (C) 2012 Elsevier B.V. All rights reserved.

Multi-Walled Carbon Nanotubes and Poly(lactic acid) Nanocomposite Fibrous Membranes Prepared by Solution Blow Spinning

Nanocomposite fibers based on multi-walled carbon nanotubes (MWCNT) and poly(lactic acid) (PLA) were prepared by solution blow spinning (SBS). Fiber morphology was characterized by scanning electron microscopy (SEM) and optical microscopy (OM). Electrical, thermal, surface and crystalline properties of the spun fibers were evaluated, respectively, by conductivity measurements (4-point probe), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), contact angle and X-ray diffraction (XRD). OM analysis of the spun mats showed a poor dispersion of MWCNT in the matrix, however dispersion in solution was increased during spinning where droplets of PLA in solution loaded with MWCNT were pulled by the pressure drop at the nozzle, producing PLA fibers filled with MWCNT. Good electrical conductivity and hydrophobicity can be achieved at low carbon nanotube contents. When only 1 wt% MWCNT was added to low-crystalline PLA, surface conductivity of the composites increased from 5 x 10(-8) to 0.46 S/cm. Addition of MWCNT can slightly influence the degree of crystallinity of PLA fibers as studied by XRD and DSC. Thermogravimetric analyses showed that MWCNT loading can decrease the onset degradation temperature of the composites which was attributed to the catalytic effect of metallic residues in MWCNT. Moreover, it was demonstrated that hydrophilicity slightly increased with an increase in MWCNT content. These results show that solution blow spinning can also be used to produce nanocomposite fibers with many potential applications such as in sensors and biosensors.

Hofmeister effects on the colloidal stability of poly(ethylene glycol)-decorated nanoparticles

The colloidal stability of poly(ethylene glycol)-decorated poly(methyl methacrylate), PMMA/Tween-20, particles was investigated by means of phase separation measurements, in the presence of sodium fluoride (NaF), sodium chloride, sodium bromide, sodium nitrate, or sodium thiocyanate (NaSCN) at 1.0 mol L-1. Following Hofmeister's series, the dispersions of PMMA/Tween-20 destabilized faster in the presence of NaF than with NaSCN. After the phase separation, the systems were homogenized and except for the dispersions in NaF, re-dispersed particles took longer to destabilize, indicating that anions adsorbed on the particles, creating a new surface. Except for F- ions, the adsorption of anions on the polar outmost shell was evidenced by means of tensiometry and small-angle X-ray scattering measurements. Fluoride ions induced the dehydration of the polar shell, without affecting the polar shell electron density, and the formation of very large aggregates. A model was proposed to explain the colloidal behavior in the presence of Hofmeister ions.

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.

Photoconduction action spectra of regio-regular poly(3-hexylthiopene):TiO2 diodes

The development of polymer-based photovoltaic devices brings the promise of low-cost and lightweight solar energy conversion systems. This technology requires new materials and device architectures with enhanced efficiency and lifetime, which depends on the understanding of charge-transport mechanisms. Organic films combined with electronegative nanoparticles may form systems with efficient dissociation of the photogenerated excitons, thus increasing the number of carriers to be collected by the electrodes. In this paper we investigate the steady-state photoconductive action spectra of devices formed by a bilayer of regio-regular poly(3-hexylthiophene) (RRP3HT) and TiO2 sandwiched between ITO and aluminum electrodes (ITO/TiO2:RRP3HT/Al). Photocurrents were measured for distinct bias voltages with illumination from either side of the device. Heterojunction structures were prepared by spin coating a RRP3HT film on an already deposited TiO2 layer on ITO. Symbatic and antibatic curves were obtained and a model for photocurrent action spectra was able to fit the symbatic responses. The quantum yield increased with the electric field, indicating that exciton dissociation is a field-assisted process as in an Onsager mechanism. Furthermore, the quantum yield was significantly higher when illumination was carried out through the ITO electrode onto which the TiO2 layer was deposited, as the highly electronegative TiO2 nanoparticles were efficient in exciton dissociation.

Effect of Prior Photodegradation on the Biodegradation of Polypropylene/Poly(3-hydroxybutyrate) Blends

In this work, the effect of blend composition and previous photodegradation on the biodegradation of polypropylene/ poly(3-hydroxybutyrate) (PP/PHB) blends was studied. The individual polymers and blends with or without the addition of poly(ethylene-co-methyl acrylate- co-glycidyl methacrylate) [P(E-MA-GMA)] as a compatibilizer (in the case of 80/20 blend) were exposed to UV light for 4 weeks and their biodegradation was evaluated. The biodegradation of PHB phase within the blends was hindered as PHB was the dispersed phase and PP fibrous particles were observed at the surface of the blend samples after biodegradation. Previous photodegradation lessened PHB biodegradation but enhanced the biodegradation of PP and the blends within the biodegradation time studied. Photodegradation resulted in cracks at the surface of PP and the blends, which probably facilitated the biotic reactions due to an easier access of the enzymes to deeper polymer layers. It also resulted in a decrease of molecular weight of PP phase and formation of carbonyl and hydroxyl groups which were consumed during biodegradation. Size exclusion chromatography analysis revealed that only the short chains of PP were consumed during biodegradation.