Magnetic and elastic properties of CoFe2O4- polydimethylsiloxane magnetically oriented elastomer nanocomposites

Magnetic elastic structured composites were prepared by using CoFe 2O4 ferromagnetic and superparamagnetic nanoparticles as fillers in polydimethylsiloxane (PDMS) matrixes, which were cured in the presence of a uniform magnetic field. Cobalt-iron oxide nanoparticles of three different average sizes (between 2 and 12 nm) were synthesized and characterized. The smallest nanoparticles presented superparamagnetic behavior, with a blocking temperature of approximately 75 K, while larger particles are already blocked at room temperature. Macroscopically structured-anisotropic PDMS-CoFe2O4 composites were obtained when curing the dispersion of the nanoparticles in the presence of a uniform magnetic field (0.3 T). The formation of the particle's chains (needles) orientated in the direction of the magnetic field was observed only when loading with the larger magnetically blocked nanoparticles. The SEM images show that the needles are formed by groups of nanoparticles which retain their original average size. The Young's moduli of the structured composites are four times larger when measured along the oriented needles than in the perpendicular direction. Magnetization (VSM) and ferromagnetic resonance curves of the structured composites were determined as a function of the relative orientation between the needles and the probe field. The remanence magnetization was 30 higher when measured parallel to the needles, while the coercive field remains isotropic. These observations are discussed in terms of the individual nanoparticle's properties and its aggregation in the composites. © 2011 American Institute of Physics.Fil:Soledad Antonel, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Jorge, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Perez, O.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Martín Negri, R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Screen-printed electrochemical chromium (VI) sensing electrodes for effluent bioremediation monitoring

In this work, we introduce a simple, low-cost and acid-resistant materials system for carbon-based screen-printed electrodes (SPEs), and apply it to chemical sensing of hexavalent chromium, i.e. Cr(VI), in acid environments, as encountered in bioremediation of industrial effluents. The developed composite materials comprised of 1) dense organic-carbon conductor, 2) porous polymer-carbon-ligand active sensing material, and 3) insulating and protective dielectric. All materials were formulated with two different organic matrices, polyvinylbutyral (PVB) or epoxy resin (EP). The selected ionophore for chromium detection was diethylenetriamine-pentaacetic acid (DTPA). Both variants allowed Cr(VI) sensing over a wide concentration range in acid media

Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400 °C (in air atmosphere also). The size distribution was obtained by fitting SAXS experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0 - 0.6) nm with polydispersivity given by sigma= (8.0 ± 0.2) nm. The SAXS, XRD and TEM experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12 ± 1) nm). Nickel-based nanochains (average diameter: 360 nm; average length: 3 mm, obtained by SEM; aspect ratio=length/diameter ~10) were obtained at 85 ºC and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance spectra (FMR) and strain-stress curves of low filler´s loading composites (2% w/w of fillers) were determined as functions of the relative orientation respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR-resonance field and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.Fil: Landa, Romina Ailín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: P Soledad Antonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: Mariano M. Ruiz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Química Física de los Materiales del Medioambiente y Energía; Argentina;Fil: Oscar E Pérez. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias;Fil: Alejandro Butera. Comisión Nacional de Energía Atómica;Fil: Guillermo Jorge. Universidad Nacional de General Sarmiento;Fil: Cristiano L. P. Oliveira. Instituto de Física, Universidade De São Paulo; Brasil;Fil: Martín Negri. Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Industrias

Magnetically tuneable thermoplastic resistive composites

Depending on the materials and processing parameters, composite materials consisting of an insulating matrix and a conductive filler may be electrically insulating, resistive or conducting. Previously, we had manufactured composites consisting of a resin and a conducting magnetic filler, and shown that polymerisation under magnetic field could achieve oriented conductors, with essentially unidirectional electrical conduction. In this work, we explore the possibility of replacing the resin matrix by a thermoplastic material, allowing in principle free reconfiguration of the filler by re-melting the matrix under different magnetic field strengths and orientations, and thereby tuning of the electrical transport properties. The formulation, fabrication and first results are reported on such materials, with an ethylcellulose - wax matrix and conducting powders based on Ag-coated Fe3O4 and Fe2CoO4 ferrites

Piezo and magneto resistance of magnetically oriented dispersions of magnetic particles covered with silver in bulk and screen-printed elastomer polymers

1) Synthesis and characterization of oxide@Ag particles that are simultaneously magnetic and conductive 2) Elaboration of composites: dispersion of particles in organic matrix: silicone (PDMS) or thermoplastic (ethylcellulose + wax) 3) Screen printing of composite paste on alumina substrate 4) Curing under controllable and orientable magnetic field Composite materials with a thermoplastic matrix may be re-melted an aligned again

Benthic foraminiferal ultrastructural alteration induced by heavy metals

Heavy metals are known to cause deleterious effects on biota because of their toxicity, persistence and bioaccumulation. Here, we briefly document the ultrastructural changes observed in the miliolid foraminifer Pseudotriloculina rotunda (d\u27Orbigny in Schlumberger, 1893) and in the perforate calcareous species Ammonia parkinsoniana (d\u27Orbigny, 1839) induced by exposure to one of three heavy metals (zinc, lead, or mercury). The exposure of these two benthic foraminiferal species to the selected heavy metals appears to promote cytological alterations and organelle degeneration. These alterations include a thickening of the inner organic lining, an increase in number and size of lipid droplets, mitochondrial degeneration, and degradation vacuoles and residual body proliferation. Some of these alterations, including the thickening of the inner organic lining and the proliferation of lipids, might represent defense mechanisms against heavy metal-induced stress

Magnetoresistencia y elasticidad anisotrópica en elastómeros formados por cadenas de nanopartículas y nanotubos orientadas magnéticamente [magnetoresistance and anisotropic elasticity in elastomers formed by chains of magnetically oriented nanoparticles and nanotubes]

La meta de éste trabajo es obtener magneto-elastómeros compuestos por dispersión de nanopartículas magnéticas en polidimetilsiloxano (PDMS), curando el polímero en presencia de un campo magnético uniforme. [Le but de ce travail est d’obtenir des composites magnéto-élastomériques par dispersion de nanoparticules magnétiques dans du polydiméthylsiloxane (PDMS), en réticulant le polymère en présence d’un champ magnétique uniforme.] [The goal of this work is to obtain magneto-elastomeric composites through dispersion of magnetic nanoparticles in polydimethylsiloxane (PDMS), by curing the polymer in presence of a uniform magnetic field.

La renovación de la palabra en el bicentenario de la Argentina : los colores de la mirada lingüística

El libro reúne trabajos en los que se exponen resultados de investigaciones presentadas por investigadores de Argentina, Chile, Brasil, España, Italia y Alemania en el XII Congreso de la Sociedad Argentina de Lingüística (SAL), Bicentenario: la renovación de la palabra, realizado en Mendoza, Argentina, entre el 6 y el 9 de abril de 2010. Las temáticas abordadas en los 167 capítulos muestran las grandes líneas de investigación que se desarrollan fundamentalmente en nuestro país, pero también en los otros países mencionados arriba, y señalan además las áreas que recién se inician, con poca tradición en nuestro país y que deberían fomentarse. Los trabajos aquí publicados se enmarcan dentro de las siguientes disciplinas y/o campos de investigación: Fonología, Sintaxis, Semántica y Pragmática, Lingüística Cognitiva, Análisis del Discurso, Psicolingüística, Adquisición de la Lengua, Sociolingüística y Dialectología, Didáctica de la lengua, Lingüística Aplicada, Lingüística Computacional, Historia de la Lengua y la Lingüística, Lenguas Aborígenes, Filosofía del Lenguaje, Lexicología y Terminología

Molecular rotational diffusion detected by differential fluorescence energy

Includes bibliographical references (page 257).In this paper, we present a complete study of the influence of the molecular rotational diffusion movement in the fluorescence signal when a sample is excited by two short pulses. The study includes the calculations of this effect for ellipsoidal molecules. Experimental results are presented that show a fluorescence behavior influenced by the molecular rotational diffusion movement with temporal characteristics that agree with our calculations