Materials Science Forum Vol. 691

Abstract: In this work, a series of Pressure Sensitive Adhesives (PSAs) of poly(n-butyl acrylate-2-ethyl hexyl acrylate- acrylic acid) were synthesized via emulsion polymerization. The PSAs particles were carried out in a semicontinuous process. Synthesis was carried out in two stages of thereaction. In the first, a core of poly(butyl acrylate-co-2-ethyl hexyl acrylate) with a composition of 50/50 wt%/wt % was synthesized, while in the second stage, the core was charged in the reactor as a seed; and was recovered with a poly(butyl acrylate-co-2-ethyl hexyl acrylate-co-acrylic acid) shell. The acrylic acid in the shell was varied between 0, 1, 3 and 5 wt%. The PSAs obtained were characterized by dynamic light scattering and zeta potential. The results of dynamic light scattering showed monodispersed particles with an average particle size of 350 nm, while the zeta potential results decreased as the acrylic acid content increased. The mechanical tests showed that the increase in acrylic acid content in the particle shell improves the adhesion properties. For peel adhesion, the maximum value was reached at 3 wt% of acrylic acid.

Abstract: Cadmium Selenide (CdSe) thin films were prepared by pulsed laser deposition using a Nd:YAG laser (355 nm). Films were grown by ablating a sintered pure CdSe target with fluences from 0.1 to 1.5 J/cm² on corning glass, silicon (100) and quartz substrates. Deposition chamber was maintained under vacuum pressure while substrate temperature was increased from room temperature to 500°C in order to control the crystalline phase. All the films show mirror-like surface morphology. Atomic force microscopy (AFM) images shown that films have very flat surfaces with RMS values around 0.7 and 5 nm for room temperature and 500°C respectively. The X-ray diffraction analysis proves the presence of the cubic zinc blend phase for the CdSe films deposited at low temperature, at 400°C and at higher substrate temperature the hexagonal phase is present. TEM analysis shows that at 100°C the films are constituted by particles with an average size of 30nm in diameter. The optical properties of the films were determined from the UV-transmission spectra. The estimated band gap values of the films deposited at room temperature and at 400°C (0.1 J/cm²) were 1.87 and 1.70 eV respectively.

Abstract: We present a comparison between co-precipitation method and polyol mediated synthesis for obtaining sub-micrometric powders of Eu_0.05Ca_0.95MnO₃ manganite. The samples synthesized were characterized by XRD and SEM; where the compounds have a single phase with the proposed stoichiometry. Microwave absorption response in poly-crystalline Eu_0.05Ca_0.95MnO₃ samples that it is carried out by both methods, are compared. These measurements were carried out at X-band (9.4 GHz) with a dc magnetic field up to 6000 Gauss, at 300 K. Electron Paramagnetic Resonance (EPR) spectra show important differences between both samples, indicating that the processes of magnetic absorption and the temperatures of phase transition are sensitive to order/disorder local; that we associate with the preparation route.

Abstract: We present in this work some results concerning the effects of the thermal annealing with CdCl₂ on the optical properties of CdS thin films grown by radio-frequency planar magnetron sputtering technique, under optimized growth parameters: gas pressure, atmosphere, substrate temperature, power of plasma, etc. An improvement of the optical properties has been observed, mainly the presence of radiative emission (luminescence) at room temperature. This fact allowed us to carry out a deep study of the photoluminescence (PL) properties of the CdS films, in the range of temperature 10≤ T ≤ 300 K. Radiative emission at the high energy side has been observed and related to exitonic processes. Temperature quenching experiments gave rise to the calculation of the activation energies for each one of the radiative emissions (PL bands).

Abstract: A three dimensions mathematical modeling was developed with COMSOL 3.2 software of an electroremediation cell. The Navier Stokes and Darcy equations were used to model the behavior of the electrolyte and the sand, respectively. The mass balance for hydrogen ion was carried out with Nernst-Planck equation for the anode and soil regions. The main factors that contribute to the hydrogen ion balance were the diffusive flux and electric migration. The mathematical modeling was validated with an experimental arrangement consisted in an electroremediation cell which contains sand as porous medium and water as electrolyte. A potential of 20 V was applied for 24 hours and the pH was measured continuously. The results of the model are in good agreement with those obtained experimentally.