Photo-oxidation of polyphenylenevinylene chains in Langmuir-Blodgett and cast films

Poly(p-phenylene vinylene) (PPV) derivatives are well known for their applications in polymer light emitting diodes (PLEDs). These derivatives are highly susceptible to photooxidation though, which is mainly caused by the scission of the vinyl double bond on the polymer backbone. In this work, we show that Langmuir-Blodgett (LB) films are less degraded than cast films of a PPV derivative (OC1OC6-PPV). Both films had similar thickness (∼50 nm) to allow for a more realistic comparison. Photodegradation experiments were carried out by illuminating the films with white light from a halogen lamp (50W, 12 V), placed at a fixed dstance from the sample. The decay was monitored by UV-Vis and FTIR spectroscopies. The results showed that cast films are completely degraded in ca. 300 min, while LB took longer times, ca. 1000 min, i.e. 3 times the values for the cast films. The degradation process occurs in at least two stages, the rates of which were calculated assuming that the reaction follows a first order kinetics. The characteristic times for the first stage were 3.6×10-2 and 1.3×10-3 min-1 for cast and LB films, respectively. For the second stage the characteristic times were 5.6×10-2 and 5.0×10 -3 min-1. 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.

Caracterização da mobilização das reservas das sementes do maracujá-amarelo (Passiflora edulis Sims f. flavicarpa O. Deg) durante a germinação

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pesquisa de segunda neoplasia em boca e orofaringe em pacientes portadores de carcinoma espinocelular (CEC) de esôfago, boca e orofaringe através de narrow band imaging (NBI)

Pós-graduação em Pesquisa e Desenvolvimento (Biotecnologia Médica) - FMB

Deposição e caracterização de filmes finos de GaAs e 'Al IND. 2''O IND. 3' para potencial utilizado em transistores

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Estudo da eficiência fotocatalítica em função da morfologia de nanoestruturas de TiO2 síntetizadas pelo método hidrotérmico

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aspectos ecofisiológicos da germinação de sementes de mulateiro (Calycophyllum spruceanum Benth.) Rubiaceae

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Ecologia da germinação de sementes e desenvolvimento de plantas de Platymiscium floribundum Vog. (Sacambu) - Fabaceae em viveiro e sob dossel de floresta ombrófila densa, São Paulo, SP

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Geração de segundo harmônico em vidros teluritos TeO2 – LiNbO3

Pós-graduação em Ciência dos Materiais - FEIS

Efeito da terapia fotodinâmica antimicrobiana mediada por curcumina sobre Streptococcus Mutans

Pós-graduação em Ciências Odontológicas - FOAR

Role of the reactive atmosphere during the sol-gel synthesis on the enhancing of the emission quantum yield of urea cross-linked tripodal siloxane-based hybrids

Transparent monoliths and films of urea cross-linked tripodal siloxane-based hybrids (named tri-ureasils) were prepared by the sol-gel process, under controlled atmosphere (inside a glove box) and ambient conditions and their structure and optical features were compared. X-ray diffraction data point out that all the materials are essentially amorphous and Si-29 NMR reveal an increase in the condensation degree (0.97) for the hybrids prepared under controlled atmosphere relatively to that found for those prepared under ambient conditions (0.84-0.91). The tri-ureasils are white light emitters under UV/Visible excitation (from 250 to 453 nm) being observed for the composites prepared inside the glove box a significant enhancement (60-80 %) of the absorption coefficient and higher emission quantum yield values (similar to 0.27 and similar to 0.20 for monoliths and films, respectively) relatively to those synthesized under ambient condition.

Influência de protetores físicos coloridos nas trocas gasosas de Canafístula (Peltophorum dubium (Spreng.) Taub.)

The aim of this experiment was to study the influence of transparent, blue and red tree shelters on gas exchanges of canafístula’s (Peltophorum dubium (Spreng.) Taub.) seedlings. This study was carried out in Department of Botany, Institute of Biosciences, U ESP, Botucatu, São Paulo State, Brazil. The experiment design was randomized blocks, with 5 replications, each one containing 6 units of each treatment (nonsheltered, transparent tree shelters, blue tree shelters and red tree shelters). The evaluations of gas exchanges were made through an infrared gas analyzer. It follows that the tree shelters use may limit the photosynthesis, increase the transpiration and stomatal opening, besides reducing the water use efficiency. The colored tree shelters use created unfavorable conditions for the development, reducing the photosynthesis, because they reflected the blue and red wavelengths, allowing only the passage of the other components of the white light or of the photosynthetically active radiation

Terapia fotodinâmica e luz branca: aspectos analíticos e perspectivas da viabilidade do tratamento

Photodynamic Therapy (PDT) is a technique used to treat several types of lesions, such as cancer, microbial control, and esthetic dentistry cases. The performance of PDT involves the use of a photosensitizer (PS), which mainly will be located in cancer cells and is irradiated with visible light. This process, when it occurs in the presence of oxygen triggers the formation of reactive oxygen species that are cytotoxic to cells. These species cause cell death and subsequent tumor necrosis. The use of white light as a light source for multispectral Photodynamic Therapy and its consequences to the photodynamic effect is not yet completely established, and therefore there is interest in studying the parameters involved for analyzing the best conditions for applying treatment. The wavelength is crucial to improve the therapeutic effect, since both the optical properties of the biological tissue as the PS depend on these parameters. For FS studied in this work (Photogem®) are most often used wavelengths in the red region, due to their larger penetration depth in biological tissue. Thus, the light source becomes a fundamental aspect, their choice depends on the specific application and is based on the tumor location, light dose to be delivered and FS chosen. Despite all the advantages presented by lasers, the fact of having an emission spectrum essentially monochrome makes only one possible transition possible for the absorption of FS is used. Therefore, more extensive light sources such as light emitting diodes (LED), could be better used in some cases the laser, with the additional advantage of a reduced cost. Therefore, the choice of the white LED comes from an emission spectrum that still wider LED colors defined by allowing greater use of the several absorption bands and with varying depths of operation, according to the wavelength... (Complete abstract click electronic access below)

A semente de Passiflora edulis Sims f. flavicarpa O. Deg. (Maracujá-Amarelo) durante a germinação e crescimento inicial da plântula: a dinâmica de lipídios, carboidratos e cloroplastos, e sua relevância nesse período

Pós-graduação em Ciências Biológicas (Biologia Vegetal) - IBRC

Effects of humidity on the electrical properties of thermal inkjet-printed films of copper tetrasulfonated phthalocyanine (CuTsPc) onto paper substrates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Permeabilidade a água e germinação de sementes heteromórficas de Bowdichia virgilioides Kunth

Pós-graduação em Ciência Florestal - FCA