Browsing by Author "Oliveira Junior, Osvaldo Novais de"

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    Energy transfer in nanostructured films containing poly(p-phenylene vinylene) and acceptor species.
    (2009) Postacchini, Bruna Bueno; Zucolotto, Valtencir; Dias, Fernando B.; Monkman, Andy; Oliveira Junior, Osvaldo Novais de
    The combination of luminescent polymers and suitable energy-accepting materials may lead to a molecularlevel control of luminescence in nanostructured films. In this study, the properties of layer-by-layer (LbL) films of poly(p-phenylene vinylene) (PPV) were investigated with steady-state and time-resolved fluorescence spectroscopies, where fluorescence quenching was controlled by interposing inert polyelectrolyte layers between the PPV donor and acceptor layers made with either Congo Red (CR) or nickel tetrasulfonated phthalocyanine (NiTsPc). The dynamics of the excited state of PPV was affected by the energy-accepting layers, thus confirming the presence of resonant energy transfer mechanisms. Owing to the layered structured of both energy donor and acceptor units, energy transfer varied with the distance between layers, r, according to 1/rn with n ) 2 or 3, rather than with 1/r6 predicted by the Fo¨rster theory for interacting point dipoles.
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    Enzyme immobilization on Ag nanoparticles/polyaniline nanocomposites.
    (2009) Crespilho, Frank Nelson; Iost, Rodrigo Michelin; Travain, Silmar Antonio; Oliveira Junior, Osvaldo Novais de; Zucolotto, Valtencir
    The performance of the modified electrodes toward urea hydrolysis was investigated via amperometric measurements, revealing a fast increase in cathodic current with a well-defined peak upon addition of urea to the electrolytic solution. The cathodic currents for the ITO/PAni/PVA–AgNP/urease electrodes were significantly higher than for the ITO/PAni/urease electrodes. The friendly environment provided by the ITO/PAni/PVA–AgNP electrode to the immobilized enzyme promoted efficient catalytic conversion of urea into ammonium and bicarbonate ions. Using the Michaelis–Menten kinetics equation, a KM app of 2.7mmolL−1 was obtained, indicating that the electrode architecture employedmay be advantageous for fabrication of enzymatic devices with improved biocatalytic properties.
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    The influence of preparation method of OC1OC6-PPV films on the photo-oxidation process.
    (2006) Olivati, Clarissa de Almeida; Ferreira, Marystela; Bianchi, Rodrigo Fernando; Faria, Roberto Mendonça; Oliveira Junior, Osvaldo Novais de; Balogh, Débora Terezia
    Poly( p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). PPV derivatives are highly susceptible to photo-oxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that LangmuireBlodgett (LB) films are less degraded than cast films of a PPV derivative (OC1OC6-PPV). Both films had similar thickness (w50 nm) to allow for a more realistic comparison. Degradation was monitored with UVevis and FTIR spectroscopies. The results indicated that cast films were completely degraded in ca. 400 min, while LB took longer time, i.e. about four times the values for the cast films. The differences can be attributed to the more compact morphology in the LB than in the cast films. With a compact morphology the diffusion of oxygen in the LB film is hampered and this causes a delay in the degradation process.