Materials Science Forum Vol. 644

Abstract: Precession electron diffraction (PED) is a new promising technique for electron diffraction pattern collection under quasi-kinematical conditions (as in X-ray Diffraction), which enables “ab-initio” solving of crystalline structures of nanocrystals. The PED technique may be used in TEM instruments of voltages 100 to 400 kV and is an effective upgrade of the TEM instrument to a true electron diffractometer. The PED technique, when combined with fast electron diffraction acquisition and pattern matching software techniques, may also be used for the high magnification ultra-fast mapping of variable crystal orientations and phases, similarly to what is achieved with the Electron Backscattered Diffraction (EBSD) technique in Scanning Electron Microscopes (SEM) at lower magnifications and longer acquisition times.

Abstract: Aluminum-based nanocomposites have been produced by mechanical milling, introducing silver nanoparticles within the matrix of a 7075 aluminum alloy using a high energy ball mill. The milled products were compacted by uniaxial load and pressure-less sintered under argon atmosphere, and finally hot extruded. Silver nanoparticles are well dispersed into the matrix of the powder particles as well as in the matrix of the extruded material. Transmission electron microscopy (TEM) analyses are used to corroborate and understand the hypothesis that second-phase particles finely and homogeneously dispersed in the matrix give greater strength to the material. In addition to the strengthening effect, the nanoparticles act like a process control agent (PCA) since the crystallite size of the nanocomposite is smaller at higher contents of nanoparticles.

Abstract: A magnetic polyvinylchloride (PVC) nanocomposite was prepared by static casting using a plasticizer-based ferrofluid. Two sets of nanocomposites were prepared: one under the influence of magnetic field and the other without magnetic field. The effects of ferrofluid content and the magnetic field on the magnetic and mechanical properties of the nanocomposite were studied in detail. Magnetite (Fe3O4) nanoparticles used for the ferrofluid preparation were prepared by the chemical co-precipitation method. Dioctyl phtalate (DOP)-based ferrofluid was prepared by the peptization technique. X-ray diffraction (XRD) was used to characterize the superparamagnetic behavior of the nanocomposite. A Universal tensometer was used to evaluate their mechanical properties. The results showed that the magnetization value of the nanocomposites increased as a function of ferrofluid concentration with all the samples showing superparamagnetic behavior. The mechanical studies showed that the tensile strength and elongation at break of the magnetic PVC nanocomposite were increased by the addition of ferrofluid and the applied magnetic field.

Abstract: A study of the effect of an ionomer compatibilizer (surlyn® 9520 and 9721, both with zinc as the neutralizing cation) on the morphology and properties of a high density polyethylene (HDPE) - montmorillonite clay nanocomposite was carried out. The nanoclay used was cloisite 20A®. Polyethylene /Ionomer /Clay nanocomposites were prepared via melt mixing in a twin screw extruder. The nanoclay dispersion and exfoliation were examined through X-Ray Difraction (XRD) and Scanning Electron Microscopy (SEM). TGA was carried out to determine the effect of nanoclay on the thermal stability of the HDPE nanocomposites. Results showed that both ionomers impart a marked compatibility between the polymer and the nanoclay, promoting the exfoliation of the nanoclay within the HDPE matrix. Nonetheless, ionomer 9520 (with the higher degree of neutralization) at 10 and 12 wt% content produced completely exfoliated morphologies, whereas, the ionomer 9721 produced a lesser degree of exfoliation with few tactoids.

Abstract: High impact polystyrene (HIPS) is considered a heterogeneous polymeric system and is constituted by a disperse phase of rubber particles within a continuous phase formed by a polystyrene (PS) matrix. During the synthesis of HIPS, PS is formed whereas some PS chains become chemically bonded to polybutadiene (PB) chains, resulting in a PB-g-PS copolymer, which decreases the interfacial tension between both incompatible phases, acting as a compatibilizer. In this study, 2 HIPS systems were evaluated by energy dispersive spectroscopy (EDS). In the first case, a HIPS composite was analyzed by EDS to locate the graft copolymer species containing Si atoms, which were previously synthesized by anionic polymerization using chloro-silane chemistry. The graft copolymer was incorporated to the HIPS synthesis from the beginning of the reaction in order to provide an improvement on the rubber phase stability. The graft copolymer was located at the interphase between the PS occlusions and the PB subdomains of the rubber particles. In the second case, HIPS was synthesized incorporating silver nanoparticles (AgNP´s) during the polymerization reaction, where the system can exhibit different types of morphology of the elastomeric phase (micelles, lamellas and core-shell). These structures overlapped the AgNP´s in the transmission electron microscopy (TEM) images, thus resulting this technique to be inadequate to establish the location of the AgNP´s. In this context EDS was used to evaluate the location and distribution of the AgNP´s by means of the elemental composition analysis. AgNP´s were preferentially detected in the PS phase as bigger clusters.

Abstract: Organic-inorganic hybrid films were synthesized by a modified sol-gel process. PMMA-SiO2 films were prepared using methylmethacrylate (MMA), tetraethil-orthosilicate (TEOS) as silicon dioxide source, and 3-trimetoxi-silil-propil-methacrylate (TMSPM) as coupling agent. FTIR measurements were performed on the hybrid films to confirm the presence of PMMA-SiO2 bonding. In addition, metal-insulator-metal (MIM) devices were fabricated to study the dielectric constant of the films as function of frequency (1 KHz to 1 MHz). Electrical results show a weak trend of the dielectric constant of the hybrid films with MMA molar ratio. More importantly, the PMMA-SiO2 hybrid films showed a higher dielectric constant than SiO2 and PMMA layers, which is likely due to the presence of additional C-O-C bond.