Dynamic scale theory for characterizing surface morphology of layer-by-layer films of poly(o-methoxyaniline)

The dynamic scale theory and fractal concepts are employed in the characterization of surface morphological properties of layer-by-layer (LBL) films from poly(o-methoxyaniline) (POMA) alternated with poly(vinyl sulfonic acid) (PVS). The fractal dimensions are found to depend on the procedures to fabricate the POMA/PVS multilayers, particularly with regard to the drying procedures. LBL films obtained via drying in ambient air show a more homogeneous surface, compared to films dried under vacuum or a flow of nitrogen, due to a uniform rearrangement of polymer molecules during solvent evaporation.

Spectral redistribution of waveguided emission in BEH-PPV films

We report on spectral redistribution of the photoluminescence (PL) emission from the edge of thin-film planar waveguides of the conjugated polymer BEH-PPV [Poly(2,5-bis(2'-ethyl-hexyl)-1,4-phenylenevinylene] induced by self-absorption in the polymer film. The PL spectra present drastic changes and displace to longer wavelengths with increasing self-absorption. We observe an enhancement of the absolute PL intensity at longer wavelengths, which was interpreted as due to re-emission of self-absorbed photons. The significant efficiency for the PL re-emission suggests the use of self-absorption as a mechanism for tuning the emission into the near infrared.

Electrical properties of screen printed BaTiO3 thick films

The deposition of thick film pastes by screen-printing is a relatively simple and convenient method to produce thicker layers with thickness up to 100 mum. In the present work, the barium titanate thick films were prepared from mechanically activated powders based on BaC03 and TiO2. After mixing, the powders were calcined at low temperature by slow heating and cooling rates. The thick films were deposited on to Al2O3 substrates through hybrid technology. The obtained films were fired at 850 degreesC together with electrode material (silver/palladium). The electrical properties of thick films: dielectric permittivity, dielectric losses, Curie temperature, hysteresis loop were reported. The obtained BT thick films can be applied in as multilayer capacitors or in gas sensor application. (C) 2003 Elsevier Ltd. All rights reserved.

Polystyrene-type resin used for peptide synthesis: application for anion-exchange and affinity chromatography

This paper deals with an unusual application for a copolymer of styrene-1 % divinylbenzene bearing high amount of aminomethyl groups for anion-exchange and affinity chromatography. The so-called aminomethyl resin (AMR), to date only employed for peptide synthesis, swelled appreciably in water and was used successfully to purify negatively charged peptides. By correlating swelling degree of beads with pH of the media, it was possible to estimate that the AMR amino group pK(a) is approximately 5.5. In addition, the synthesized acetyl-(NANP)(3)-AMR succeeded in the affinity interaction with large antibody molecules related to malaria transmission and raised previously against this dodecapeptide sequence. (C) 2004 Elsevier B.V. All rights reserved.

Fabrication and testing of a poly(vinylidene fluoride) (PVDF) microvalve for gas flow control

A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm x 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 mu m, and a voltage of -200 V DC was used to close the device by moving the actuator 20 mu m lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

ELECTROACTIVE BLENDS OF POLY(VINYLIDENE FLUORIDE) AND POLYANILINE DERIVATIVES

The conditions for processing and doping of blends of poly(o-alkoxyaniline)s and poly(vinylidene fluoride) were investigated. Flexible, free-standing and stretchable films of blends of various compositions were obtained by casting. A low percolation threshold was observed with the onset of conductivity at low polyalkoxyaniline contents (i.e. 5%). Interestingly, these blends displayed electrochromism with colour changes similar to those of the parent conducting polymer, as observed from cyclic voltammetry measurements. This behaviour is seen even for low contents of the conducting polymer, indicating that a continuous conducting pathway, which is capable of exchanging charge, is formed within the insulating matrix.

Durango apatite fission-track dating using length-based age corrections and neutron fluence measurements by natural thorium thin films and natural U-doped glasses calibrated through natural uranium thin films

In this work, we present an approach for neutron fluence measurements based on natural thorium thin films and natural uranium-doped glasses calibrated through natural uranium thin films to be used for dating with the Fission-Track Method (FTM). This neutron dosimetry approach allows the employment of FTM even when dating is carried out using low neutron themalization facilities. Besides, it makes possible the determination of the Th/U ratio of the mineral to be dated. Durango apatite which is often employed in FTM as an age standard was analyzed. This apatite presented a fairly high Th/U ratio, 29.9 +/- 1.7. Th fissions were 18%, 12% and 10% of the total for irradiations where thermal to fast neutron flux ratios were 2.4, 4.4 and 5,2, respectively. These results show that Th fission must be considered for this apatite, when not well-thermalized irradiation facilities are used. The ratio between spontaneous and induced track length, L(S)/L(1), close to 0.89, indicates a certain amount of rejuvenation of the age of Durango apatite. Therefore, its apparent age should be corrected, the application of a technique based on track-length measurements produced a corrected age of 29.7 +/- 1.1 Ma, consistent with the independent reference age of this apatite (31.4 +/- 0.5 Ma). This result represents a support for viability of the neutron dosimetry approach studied in this work for FTM.(C) 2002 Elsevier B.V. B.V. All rights reserved.

Application of a glassy carbon electrode modified with poly(glutamic acid) in caffeic acid determination

Glassy carbon electrodes were coated with films of poly( glutamic acid) ( PG), and the modified electrode proved to be very effective in the oxidation of caffeic acid. The performance of the film was also tested with ascorbic acid, coumaric acid, ferulic acid, sinapic acid and chlorogenic acid. At pH 5.6, all the hydroxycinnamic acids yield a higher peak current intensity when oxidized after incorporation in the PG-modified electrode, and only the oxidation of ascorbic acid exhibits overpotential reduction. At pH 3.5 only caffeic and chlorogenic acid are incorporated in the modified electrode and exhibit a well-defined oxidation wave at +0.51 V and +0.48 V, which is the base for their determination. Linear calibration graphs were obtained from 9 x 10(-6) mol L-1 to 4 x 10(-5) mol L-1 caffeic acid by linear voltammetric scan and from 4 x 10(-6) mol L-1 to 3 x 10(-5) mol L-1 by square wave voltammetric scan. The method was successfully applied to the determination of caffeic acid in red wine samples without interference from other hydroxycinnamic acids or ascorbic acid.

The effect of microwave annealing on the electrical characteristics of lanthanum doped bismuth titanate films obtained by the polymeric precursor method

Lanthanum doped bismuth titanate thin films (Bi3.25La0.75Ti3O12-BLT) were produced by the polymeric precursor method and crystallized in a domestic microwave oven and in conventional furnace. Using platinum coated silicon substrates configuration, ferroelectric properties of the films were determined with remanent polarization P-r and a coercive field E-c of 3.9 mu C/cm(2) and 70 kV/cm for the film annealed in the microwave oven and 20 mu C/cm(2) and 52 kV/cm for the film annealed in conventional furnace, respectively. The films annealed in conventional furnace exhibited excellent retention-free characteristics at low infant periods indicating that BLT thin films can be a promise material for use in nonvolatile memories. on the other hand, the pinning of domains wall causes a strong decay at low infant periods for the films annealed in the microwave furnace which makes undesireable the application for future FeRAMS memories. (c) 2005 Elsevier B.V. All rights reserved.

Influence of ambient gas on the growth and properties of porous tin-doped indium oxide thin films made by pulsed laser deposition

The laser ablation method was used for depositing porous nanocrystalline indium-tin oxide thin films for gas sensing applications. Samples were prepared at different pressures using three gases (O-2, 0.8N(2):0.2O(2), N-2) and heat-treated in the same atmosphere used for the ablation process. X-ray diffraction results show that the films are not oriented and the grain sizes are in the range between 15 and 40 nm. The grains are round shaped for all samples and the porosity of the films increases with the deposition pressure. The degree of sintering after heat treatment increases for lower oxygen concentrations, generating fractures on the surface of the samples. Film thicknesses are in the range of I pm for all gases as determined from scanning electron microscopy cross-sections. Electrical resistance varies between 36.3 ohm for the film made at 10 Pa pressure in N-2 until 9.35 x 10(7) ohm for the film made at 100 Pa in O-2. (C) 2007 Elsevier B.V. All rights reserved.

Nanoscale processing of polyaniline and phthalocyanines for sensing applications

Nanostructured polyaniline-modified electrodes were fabricated via the electrostatic layer-by-layer (LbL) technique where polyaniline (PANI) was assembled with one of three tetrasulfonated metallic phthalocyanines, viz. iron (FeTsPc), nickel (NiTsPc) and copper (CuTsPc). The multilayer formation was monitored via UV-vis spectroscopy by measuring the increase in the 800 run absorption band due to PANI. Infrared spectroscopy in the transmission mode suggested specific interactions between PANI and the phthalocyanines, such as those between SO3- groups from the phthalocyanines and the protonated NH group from PANI. The films were employed to detect dopamine (DA) using cyclic voltammetry. In the presence of dopamine the PANI-based LbL films showed additional redox peaks at ca. 230 and 190 mV the oxidation peak increased linearly with the concentration of DA in the electrolytic solution. Films comprising PANI/FeTsPc were able to distinguish between DA and ascorbic acid (AA), which acts as a natural interferent in biological fluids. (c) 2005 Elsevier B.V. All rights reserved.

Morphology of poly(vinylidene fluoride) and poly(o-metoxyaniline) blends

Blends of poly(o-methoxyaniline) - POMA - and poly(vinylidene fluoride) - PVDF - of various compositions were prepared from organic solvent solutions. Flexible, free-standing and stretchable films were obtained by casting, which were characterized by conductivity measurements, electron microscopy and differential scanning calorimetry. As expected, the blends conductivity increases with increasing contents of the conducting polymer. The onset of the conductivity at low contents of conducting polymer indicates a low percolation threshold for the blends. Despite the presence of the conductive host, the blends displayed the crystalline spherulitic morphology and the beta-phase characteristic of pure PVDF. This morphology appears to be destroyed, however, if the film is stretched by zone-drawing.

Electrical characterization of in situ polymerized polyaniline thin films

The alternating conductivity, sigma*(f) = sigma'(f) + i sigma ''(f), of in situ polymerized polyaniline thin films doped with hydrochloric acid, deposited on top of an interdigitated gold line array previously deposited on glass substrates, were measured in the frequency (f) range between 0.1 Hz to 10 MHz and in the temperature range from 100 to 430 K. The results for sigma'(f) are typical of a disordered solid material: for frequencies lower than a certain hopping frequency gamma(hop), log[sigma'(f)] is frequency-independent rising almost linearly for in logf > gamma(hop). A master curve was thus obtained by plotting the real component of the conductivity using normalized scales sigma'(f)/sigma(dc) and f/gamma(hop) which is indicative of a single process operating in the whole frequency range. An expression encompassing the conduction through a disordered structure taken from previous random free energy barrier model for hopping carriers, as well a dielectric function to represent the capacitive behavior of the PAni was employed to fit the experimental results. The dielectric constant and activation energy for hopping carriers were obtained as function of the polymer doping level. (c) 2007 Elsevier B.V. All rights reserved.

NMR study of ion-conducting organic-inorganic nanocomposites poly(ethylene glycol) - Silica - LiClO4

Hybrid organic-inorganic ionic conductors, also called ormolytes, were obtained by dissolution of LiClO4 into silica/poly(ethylene glycol) matrices. Solid-state nuclear magnetic resonance (NMR) was used to probe the inorganic phase structure (Si-29) and the effects of the temperature and composition on the dynamic behavior of the ionic species (Li-7) and the polymer chains (H-1 and C-13). The NMR results between -100 and +90 degrees C show a strong correlation with ionic conductivity and differential scanning calorimetry experiments. The results also demonstrate that the cation mobility is assisted by segmental motion of the polymer, which is in agreement with the results previously reported for pure poly(ethylene oxide), PEG, electrolytes.