Edgar Reyes-Melo

Iron Oxide Nanoparticles Obtained from a Fe(II) - Chitosan Polymer Film

In this work, iron oxide nanoparticles (~5 nm) embedded in a chitosan polymer film, were synthesized. In order to obtain this nanostructured material, firstly a homogenous film of Fe(II)-chitosan was prepared. The resulting composite film has a thickness of ~140μm. Iron oxide nanoparticles were in-situ synthesized by treating the composite film with H2O2 under alkaline conditions. The morphological analysis by Transmission Electron Microscopy (TEM) shows the nanoparticles were embedded and stabilized in chitosan polymer film. The magnetic behavior was studied by magnetization measurements. The magnetization curves at room temperature showed that iron oxide nanoparticles have a superparamagnetic behavior.

Dielectric Behavior of Poly(3-Hexylthiophene)/Carbon Nanotube Composites by Broadband Dielectric Spectroscopy

Some of the most exciting novel approaches for renewable solar energy conversion are organic photovoltaic devices that take advantage of the unique properties of polymers such as poly(3-hexylthiophene) (P3HT). Although these types of devices present significant advantages (stability and price), their long-term performance has to be continuously improved. This paper describes the dielectric behavior of pristine P3HT and its nanocomposites versus temperature and frequency by using broadband dielectric spectroscopy. Dielectric spectra reveal the existence of two relaxation phenomena (¿, ß), below and above the glass transition. The ¿ relaxation is related to the crystallization phenomena, and the ß relaxation is due to dipolar polarization processes. These results can be incorporated into a continuous understanding of the electrical behaviors of such polymers, which play extremely important roles in the overall quality of photovoltaic devices that use such polymeric materials.

Characterization and Dynamics of Polymer Microactuators

A magnetic hybrid material consisting of iron oxide nanoparticles (4 nm) embedded in a polymer matrix of Na-CMC was synthesized. The synthesis was done from a chemical treatment on a precursor hybrid material previously synthesized. The structure, morphology, and magnetic properties for this magnetic hybrid material were studied by X-ray diffraction, IR spectroscopy, transmission electron microscopy, and magnetometry. Additionally, the dynamic response was analyzed in order to probe the feasibility to use this magnetic hybrid material as a bending-type actuator. The experimental results show that the responses of the deflection have a linear trend over a reasonable range, suggesting that the magnetic hybrid material can be used as bending-type actuators in small mechanical systems and devices. First simulations have also been done considering the two components of the magnetic hybrid material: the oxide iron nanoparticles and Na-CMC. The displacement response takes in account the viscoelastic properties of the polymeric matrix and the magnetization of the nanoparticles.

Self-Affine Quasi-Static Fracture of Soda-Lime Glass

In the present work we discuss the self-affine properties of the fracture surfaces of sodalime glass obtained under quasi-static conditions. The fracture surfaces are generated using a threepoint bending system in normal room conditions and under high humidity conditions. The surfaces were recorded both by Scanning Electron Microscopy and Atomic Force Microscopy, and their selfaffine properties are characterized using the Variable Bandwidth method. For both conditions it is observed that the major part of the fracture surface is occupied by the mirror zone. On the other hand, the self-affine analysis reveals that for both conditions the roughness exponent has values centred at around 0.58 with moderate dispersion, in agreement with previous results. Our findings support the hypothesis of the existence of a characteristic roughness exponent for quasi-static fracture with a value that is significantly lower than the value of 0.8 reported for rapid fracture conditions.

Molecular Dynamics of Poly 3-Hexyl Thiophene by Broadband Dielectric Spectroscopy

Some of the most exciting novel approaches for renewable solar energy conversion are the organic photovoltaic devices that take advantage of the unique properties of polymers such as poly(3-hexylthiphene) (P3HT). Although this type of devices present significant advantages (stability, price) their long-term performance has to be continuously improved. This study describes the dielectric behaviour of pristine poly(3- hexylthiophene) (P3HT) and its nanocomposites versus temperature and frequency by using broadband dielectric spectroscopy. Dielectric spectra reveal the existence of two relaxation phenomena (alpha, beta), below and above the glass transition. The a relaxation is related to the crystallization phenomena and the beta relaxation is due to dipolar polarization processes. These results can be incorporated into a continuous understanding of the electrical behaviours of such polymers, which play extremely important roles in the overall quality of photovoltaic devices that use such polymeric materials.