Luiz C. P. Almeida

Photoelectrochemical, photophysical and morphological studies of electrostatic layer-by-layer thin films based on poly(p-phenylenevinylene) and single-walled carbon nanotubes

The preparation of multilayer films based on poly(p-phenylenevinylene) (PPV) and carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) by electrostatic interaction using the layer-by-layer (LbL) deposition method is reported herein. The multilayer build-up, monitored by UV-Vis and photoluminescence (PL) spectroscopies, displayed a linear behavior with the number of PPV and SWNT-COOH layers deposited that undergo deviation and spectral changes for thicker films. Film morphology was evaluated by AFM and epifluorescence microscopies showing remarkable changes after incorporation of SWNT-COOH layers. Films without SWNT show roughness and present dispersed grains; films with SWNT-COOH layers are flatter and some carbon nanotube bundles can be visualized. The photoinduced charge transfer from the conducting polymer to SWNT-COOH was analyzed by PL quenching either by the decrease of the emission intensity or by the presence of dark domains in the epifluorescence micrographs. Photoelectrochemical characterization was performed under white light and the films containing SWNT-COOH displayed photocurrent values between 2.0 μA cm(-2) and 7.5 μA cm(-2), as the amount of these materials increases in the film. No photocurrent was observed for the film without carbon nanotubes. Photocurrent generation was enhanced and became more stable when an intermediate layer of PEDOT:PSS was interposed between the active layer and the ITO electrode, indicating an improvement in hole transfer to the contacts. Our results indicate that these multilayer films are promising candidates as active layers for organic photovoltaic cells.

Análise da resistência característica à compressão do concreto em blocos sobre três estacas

In this paper a numerical analysis of three-pile caps is developed to study the influence of concrete compressive characteristic strength in pile caps resistance capacity. A three-pile cap model derived from Miguel’s [1] work was adopted. From this model, variations on the compressive characteristic strength were made in order to observe modifications in its structural behavior. The numerical analysis was developed with finite element software ATENA 3D [2]. The results demonstrated that an increase in the compressive characteristic strength was not followed by a significant increment in pile cap’s strength, since models’ ruin were due to concrete splitting (opening cracks parallel to principal compressive stresses as a result of perpendicular tension stresses within the structure) and ties steel bars yielding. In the models analyzed high-tension stresses were developed along the struts and at the bottom of the pile cap’s section, demonstrating that pile cap’s ultimate resistance is not influenced by the compressive strength.

Analysis of the influence of column reinforcement anchorage length in a concrete two-pile cap

Resumo This paper describes the parametric analysis applied to assess the influence of column anchorage-reinforcement length on concrete two-pile caps under uniform compression. The non-linear numerical analysis was conducted with the bi-dimensional elements of ATENA 2D software, considering perfect adherence between steel and concrete. Simulation was based on the experimental reference model by Munhoz [1], which was the parameter adopted to validate the numerical modeling. From the validated model, four different anchorage reinforcement lengths were adopted, 34,0 cm, 20,0 cm, 10,0 cm e 3,0 cm, in order to compare pile caps behavior after these changes. Pile cap simulations presented similar behavior, i.e., column anchorage reinforcement length is not a preponderant factor for the internal mechanisms that regulate the function of these elements.

Análise numérica tridimensional de blocos sobre duas estacas

This paper compares the results between a non-linear three-dimensional numerical analysis of pile caps with two piles and the experimental study conducted by Delalibera. It is verified the load-carrying capacity, the crack pattern distribution, the principal stress in concrete and steel, the deflection and the fracture of the pile cap. The numerical analysis is executed with the finite-element software ATENA 3D, considering a perfect bond between concrete and steel. The numerical and experimental results are presented and have demonstrated a good approximation, reasserting the results of the experimental model and corroborating the theory.

Organic and Hybrid Solar Cells Based on Small Molecules

In this chapter, the recent literature involving small molecule-based organic solar cells (OSCs) will be reviewed. The number of papers published in the fields of organic semiconductor and OSCs has grown exponentially in the past decade. Such growth is stimulated by the exciting properties of these materials, combined with the possibility to produce colored, flexible, transparent and cheap solar cells. The main focus of this review is to give an overview and a perspective of the recent advances in this area, highlighting the most interesting results, novel materials as well as their limitations and challenges. This chapter will explore the properties and applications of several classes of small organic molecules, as electron donors and acceptors, dyes, and hole transport materials. Different architectures and techniques will be also discussed in the assembly of double, heterojunction, and multilayer films.