Resistance of Cyanobacterial Fouling on Architectural Paint Films to Cleaning by Water Jet

Mortar panels painted with three different white acrylic coatings were exposed to the environment in urban (So Paulo) and rural (Pirassununga) sites in Brazil for 7 years. After this time, all panels were almost equally discoloured, and paint detachment was observed to only a small degree. The biofilms were composed mainly of cyanobacteria and filamentous fungi, principal genera being Gloeocapsa and Chroococcidiopsis of the cyanobacteria, and Cladosporium and Alternaria of the fungi. Two of the three paints in Pirassununga became covered by a pink film that contained red-encapsulated Gloeocapsa and clay particles. The third, an 800% elastomeric matt formulation, became discoloured with a grey, only slightly pink, film, although the same cyanobacteria were present. The levels of paint detachments from all films in both locations were low, with rating range of 0-1 of a maximum 5 (100% detachment). After high-pressure water jetting, paint detachments increased at both locations, up to 2 in Pirassununga and 3 in So Paulo. Discoloration decreased; L*A*B* analysis of surface discoloration showed that Delta E (alteration in colour from the original paint film) changed from 28-39 before cleaning to 13-16 afterwards. The pink coloration was not entirely removed from Pirassununga samples, suggesting that cyanobacterial cells are difficult to detach, and microscopic analysis of the biofilms confirmed that Gloeocapsa was still present as the principal contaminant on all surfaces, with Chroococcidiopsis being present as the second most common. Almost no fungi were detected after water jet application.

Langmuir and Langmuir-Blodgett films of a quinoline-fluorene based copolymer

The fabrication of Langmuir-Blodgett (LB) films of synthetic polymers allows the control of molecular architecture in order to optimize physical properties. In this paper, the surface chemistry of a quinoline-fluorene based copolymer spread on the air-water interface is investigated. Surface pressure-area isotherms as well as Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) were employed to characterize the films, which could be transferred to solid supports by the LB technique. Atomic force microscopy as well as UV-Vis and fluorescence spectroscopies have shown a regular deposition of the polymers, and the luminescence properties could be controlled with the number of layers deposited on the solid support. As a result, the photoluminescence of the LB films was considerably higher than that observed for the spin coated film, and the maximum emission peak was shifted to higher energies, which is attributed to the molecular-level interactions within the layer-ordered structure of the LB film. The luminescence response would possibly be tuned to approach the highest level, which allows the films to be employed in future applications in efficient optical devices such as organic light-emitting diodes (OLEDs). (C) 2011 Elsevier B.V. All rights reserved.

Synthesis of a functionalized europium complex and deposition of luminescent Langmuir-Blodgett (LB) films

The synthesis, characterization and formation of Langmuir-Blodgett (LB)films for the luminescent [(C12H25)(2)(CH3)(2)N][Eu(tta)(4)] complex, where [(C12H25)(2)(CH3)(2)](N+) is didodecyldimethylammonium and the tta ligand is thenoyltrifluoroacetone, are reported. The coordination of tta ligands to the Eu3+ ion was confirmed by FTIR spectroscopy and the emission spectrum comprised bands corresponding to D-5(0) -> F-7(0-4) transitions. The lifetime (tau) from the emission state (D-5(0))was 0.41 ms, measured by monitoring the hypersensitive D-5(0) -> F-7(2) transition, with the curve being fitted with a first-order exponential function. The surface pressure-area isotherm indicated that the anionic complex may form condensed structures at the air-water interface due to the amphiphilic properties of the counter ion and the beta-diketone ligand. Y-type LB films of [(C12H25)(2)(CH3)(2)N][Eu(tta)(4)] were deposited on quartz substrates, with preserved luminescence and a band assigned to the D-5(0) -> F-7(2) transition. The molecular arrangement at the air/water interface and the preserved luminescence in LB films are consistent with theoretical predictions using a semi-empirical Sparkle/AM1 calculation method for the molecule in vacuum. These tools were used for the first time to predict the behavior of organized films.

Enhancement of optical absorption by modulation of the oxygen flow of TiO2 films deposited by reactive sputtering

Oxygen-deficient TiO2 films with enhanced visible and near-infrared optical absorption have been deposited by reactive sputtering using a planar diode radio frequency magnetron configuration. It is observed that the increase in the absorption coefficient is more effective when the O-2 gas supply is periodically interrupted rather than by a decrease of the partial O-2 gas pressure in the deposition plasma. The optical absorption coefficient at 1.5 eV increases from about 1 x 10(2) cm(-1) to more than 4 x 10(3) cm(-1) as a result of the gas flow discontinuity. A red-shift of similar to 0.24 eV in the optical absorption edge is also observed. High resolution transmission electron microscopy with composition analysis shows that the films present a dense columnar morphology, with estimated mean column width of 40nm. Moreover, the interruptions of the O-2 gas flow do not produce detectable variations in the film composition along its growing direction. X-ray diffraction and micro-Raman experiments indicate the presence of the TiO2 anatase, rutile, and brookite phases. The anatase phase is dominant, with a slight increment of the rutile and brookite phases in films deposited under discontinued O-2 gas flow. The increase of optical absorption in the visible and near-infrared regions has been attributed to a high density of defects in the TiO2 films, which is consistent with density functional theory calculations that place oxygen-related vacancy states in the upper third of the optical bandgap. The electronic structure calculation results, along with the adopted deposition method and experimental data, have been used to propose a mechanism to explain the formation of the observed oxygen-related defects in TiO2 thin films. The observed increase in sub-bandgap absorption and the modeling of the corresponding changes in the electronic structure are potentially useful concerning the optimization of efficiency of the photocatalytic activity and the magnetic doping of TiO2 films. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4724334]

Laminated Tubular-channel Ferroelectret Systems from Low-density Polyethylene Films and from Fluoroethylene-propylene Copolymer Films - A Comparison

A template-based lamination technique for the manufacture of ferroelectrets from uniform electret films was recently reported. In the present work, this technique is used to prepare similar ferroelectret structures from low-density polyethylene (LDPE) films and from fluoro-ethylene-propylene (FEP) copolymer films. A comparative analysis of the pressure-, temperature-, and frequency-dependent piezoelectric properties has been performed on the two ferroelectret systems. It is observed that the FEP ferroelectrets exhibit better piezoelectric responses and are thermally more stable. The difference between the piezoelectric d(33) coefficients of the two ferroelectret systems is partially explained here by their different elastic moduli. The anti-resonance peaks of both structures have been investigated by means of dielectric resonance spectroscopy and electroacoustic sound-pressure measurements. A difference of more than 10 kHz is observed between the anti-resonance frequencies of the two ferroelectret systems.

Very Intense Distinct Blue and Red Photoluminescence Emission in MgTiO3 Thin Films Prepared by the Polymeric Precursor Method: An Experimental and Theoretical Approach

MgTiO3 (MTO) thin films were prepared by the polymeric precursor method with posterior spin-coating deposition. The films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates and heat treated at 350 degrees C for 2 h and then heat treated at 400, 450, 500, 550, 600, 650 and 700 C for 2 h. The degree of structural order disorder, optical properties, and morphology of the MTO thin films were investigated by X-ray diffraction (XRD), micro-Raman spectroscopy (MR), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) measurements, and field-emission gun scanning electron microscopy (FEG-SEM) to investigate the morphology. XRD revealed that an increase in the annealing temperature resulted in a structural organization of MTO thin films. First-principles quantum mechanical calculations based on density functional theory (B3LYP level) were employed to study the electronic structure of ordered and disordered asymmetric models. The electronic properties were analyzed, and the relevance of the present theoretical and experimental results was discussed in the light of PL behavior. The presence of localized electronic levels and a charge gradient in the band gap due to a break in the symmetry are responsible for the PL in disordered MTO lattice.