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This work describes an enhanced corona triode with constant current adapted to characterize the electrical properties of thin dielectric films used in organic electronic devices. A metallic grid with a high ionic transparency is employed to charge thin films (100 s of nm thick) with a large enough charging current. The determination of the surface potential is based on the grid voltage measurement, but using a more sophisticated procedure than the previous corona triode. Controlling the charging current to zero, which is the open-circuit condition, the potential decay can be measured without using a vibrating grid. In addition, the electric capacitance and the characteristic curves of current versus the stationary surface potential can also be determined. To demonstrate the use of the constant current corona triode, we have characterized poly(methyl methacrylate) thin films with films with thicknesses in the range from 300 to 500 nm, frequently used as gate dielectric in organic field-effect transistors.

This work describes the experimental apparatus based on the Mach-Zehnder interferometer for measuring the electro-optic coefficient during and after the photo-assisted poling process using a continuous light excitation. We also show that the poling can be performed at cryogenic temperatures. The setup is based on the superposition of a Mach-Zehnder AC modulation voltage on the DC bias voltage required to promote the chromophore orientation during light excitation. The effect of the reversible polarization due to the DC bias voltage applied to the polymer film is considered to calculate the electro-optic coefficient during the photo-assisted poling process. The usefulness of our setup is demonstrated with three polymer films, with different electro-optic activities: guest-host, copolymer, and homopolymer, all based on methyl methacrylate monomers and containing disperse red-1 chromophores.

We present a compact and easy to handle instrument developed to perform rapid analysis of liquids utilizing an "electronic tongue" system. Briefly, the e-tongue used here is based on impedance measurements of an array of sensing units fabricated with ultrathin films of different materials deposited onto gold interdigitated electrodes. The instrument has the capability of measuring up to eight different sensor sets, each comprising an array of eight sensing units, and can perform a series of measurements in less than half of an hour. Additionally, there is a user-friendly software interface for instrument control, allowing the statistical correlation of samples using principal component analysis.

Azobenzene-containing molecules have been studied for a number of applications exploiting the efficient trans-cis-trans photoisomerization cycles, which lead to molecular alignment and even micrometer-scale mass transport. One of the limitations of these materials, though, is the slow dynamics of the alignment process that requires significant molecular rearrangement. In this paper, we report on Langmuir-Blodgett (LB) films of a derivative of azocrown ether, referred to as 29-membered diazocrown ether, specially synthesized for the photoisomerization to involve only distortion of the shape of the crown. As a result, the dynamics of the writing process was extremely fast, with maximum birefringence being reached within less than 1 s, to be contrasted with tens or even hundreds of seconds for other azobenzene materials. A disadvantage is this strategy, however, is that the resulting birefringence was low, of the order of 10(-3), because the closely packed arrangement prevented the whole diazocrown molecule to be fully reoriented. From a comparison with results obtained in guest-host, cast films where the 29-membered diazocrown ether was incorporated into a polystyrene matrix, we confirmed that both fast dynamics and small birefringence features are due to a combination of effects from the nanostructured nature of the LB films and the molecular structure of the specially-designed diazocrown ether. Significantly, the fast dynamics opens the way for various applications, as in command surfaces for liquid crystal devices.

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.

Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to approximately 25 nm. The film growth process was monitored by measuring the UV-vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponent n=3, thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition.

Electrostatic interactions govern most properties of polyelectrolyte films, as in the photoinduced birefringence of azo-containing polymers. In this paper we report a systematic investigation of optical storage characteristics of cast and layer-by-layer (LbL) films of poly[1 -[4-(3-carboxy-4 hydroxyphenylazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). Birefringence was photoinduced faster in PAZO cast films prepared at high pHs, with the characteristic writing times decreasing almost linearly with the pH in the range between 4 and 9. This was attributed to an increased free volume for the azochromophores with the enhanced electrostatic repulsion in PAZO charged to a greater extent. In contrast, in LbL films of PAZO alternated with poly(allylamine hydrochloride) (PAH), the electrostatic interactions between the oppositely charged polymers hampered photoisomerization and molecular rearrangement, thus leading to a slower writing kinetics for highly charged

The influence of small amounts of bovine serum albumin (BSA) (nM concentration) on the lateral organization of phospholipid monolayers at the air-water interface and transferred onto solid substrates as one-layer Langmuir-Blodgett (LB) films was investigated. The kinetics of adsorption of BSA onto the phospholipid monolayers was monitored with surface pressure isotherms in a Langmuir trough, for the zwitterionic dipalmitoylphosphatidyl ethanolamine (N,N-dimethyl-PE) and the anionic dimyristoylphosphatidic acid (DMPA). A monolayer of N,N-dimethyl-PE or DMPA incorporating BSA was transferred onto a solid substrate using the Langmuir-Blodgett technique. Atomic force microscopy (AFM) images of one-layer LB films displayed protein-phospholipid domains, whose morphology was characterized using dynamic scaling theories to calculate roughness exponents. For DMPA-BSA films the surface is characteristic of self-affine fractals, which may be described with the Kardar-Parisi-Zhang (KPZ) equation. On the other hand, for N,N-dimethyl-PE-BSA films, the results indicate a relatively flat surface within the globule. The height profile and the number and size of globules varied with the type of phospholipid. The overall results, from kinetics of adsorption on Langmuir monolayers and surface morphology in LB films, could be interpreted in terms of the higher affinity of BSA to the anionic DMPA than to the zwitterionic N,N-dimethyl-PE. Furthermore, the effects from such small amounts of BSA in the monolayer point to a cooperative response of DMPA and N,N-dimethyl-PE monolayers to the protein.

We report on the use of dynamic scale theory and fractal analyses in the study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed on glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The granular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains. The growth outside the grains was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of ca. 2.6. One could expect that inside the grains the morphology would be close to a Euclidian surface with fractal dimension of ca. 2 for any growth stage. The latter, however, was observed only for thicker films containing more than 10 bilayers. For thinner films the morphology was well described by a self-affine fractal. Such dependence of the growth behavior with the film thickness is associated with a more complete coverage of adsorption sites in thicker films due to diffusion of polymer molecules.

The phase transition from the non-polar alpha-phase to the polar beta-phase of poly(vinylidene fluoride) (PVDF) has been investigated using micro-Raman spectroscopy, which is advantageous because it is a nondestructive technique. Films of alpha-PVDF were subjected to stretching under controlled rates at 80 degrees C, while the transition to beta-PVDF was monitored by the decrease in the Raman band at 794 cm(-1) characteristic of the alpha-phase, along with the concomitant increase in the 839 cm(-1) band characteristic of the beta-phase. The alpha-->beta transition in our PVDF samples could be achieved even for the sample stretched to twice (2x-stretched) the initial length and it did not depend on the stretching rate in the range between 2.0 and 7.0 mm/min. These conclusions were corroborated by differential scanning calorimetry (DSC) and X-ray diffraction experiments for PVDF samples processed under the same conditions as in the Raman scattering measurements. Poling with negative corona discharge was found to affect the alpha-PVDF morphology, improving the Raman bands related to this crystalline phase. This effect is minimized for films stretched to higher ratios. Significantly, corona-induced effects could not be observed with the other experimental techniques, i.e., X-ray diffraction and infrared spectroscopy.

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.

The generation of surface anisotropy by photochemical means has been proposed as an attractive method to align liquid crystals. In this paper, we present an experimental study of the alignment induced on a liquid crystal by a polymer film containing azo-dye groups in the side chain. Optical measurements were performed in nematic liquid crystal cells to determine the azimuthal and zenithal anchoring strengths as a function of the irradiation energy and chromophores concentration. It was observed that the director tends to align perpendicular to the polarization direction of the incident light and the orientation process consists essentially of a rotation of the director in the plane parallel to the boundary surfaces. However, the concentration of azo-dye groups in the polymer film must exceed a minimum value to get a macroscopical effect on the liquid crystal alignment. It is shown that the azimuthal anchoring strength can be varied two orders of magnitude by controlling the irradiation energy and azo-dye concentration.