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Ciudad Universitaria, Argentina

Jorge G.A.,Laboratorio Of Bajas Temperaturas | Bekeris V.,Laboratorio Of Bajas Temperaturas | Escobar M.M.,Laboratorio Of Polimeros Y Materiales Compuestos | Goyanes S.,Laboratorio Of Polimeros Y Materiales Compuestos | And 3 more authors.
Carbon | Year: 2010

We present micro-calorimetric specific heat measurements on different multiwall carbon nanotubes of large outer diameter, as a function of temperature in the range 10-120 K. A clear anomaly at 60 K with the shape of a peak is present in two of the samples, and both the height and the characteristic temperature of the peak are independent of magnetic field and do not exhibit thermal hysteresis, discarding magnetic degrees of freedom related to Fe seeds or contributions from adsorbed gases. These features suggest that the anomaly may be caused by a structural change. As the anomaly is also unaffected by induced intertube disorder, it may be related with a melting of orientational dislocations of individual tubes within multiwall nanotubes, an effect that was theoretically predicted to occur in carbon nanotubes and represents a distinctive feature of asymmetric molecular systems. © 2009 Elsevier Ltd. All rights reserved. Source

Morales N.J.,Argentinean Institute of Chemical Physics for Materials, Environment and Energy | Goyanes S.,Laboratorio Of Polimeros Y Materiales Compuestos | Chiliotte C.,Laboratorio Of Bajas Temperaturas | Bekeris V.,Laboratorio Of Bajas Temperaturas | And 4 more authors.
Carbon | Year: 2013

A multiwall carbon nanotube (MWCNT)/hercynite (FeAl2O 4) hybrid nanomaterial was synthesized by one-step chemical vapor deposition (CVD) using acetylene as precursor and FeOx-AlOOH xerogel as catalyst. The hybrid material was composing by hercynite nanoparticles (diameter 10-50 nm) intimately attached to the walls of the MWCNTs. The diameter of the MWCNTs was related to particle size of the catalyst. The hybrid nanomaterial exhibited a characteristic magnetic behavior that can be considered as a combination of superparamagnetism and ferromagnetism, with a saturation magnetization of 5.7 emu/g at an applied field of 18 kOe and a coercivity of 520 Oe. The hybrid displayed a relatively low pHZPC (approx. 3.2) and formed very stable aqueous suspensions at pH 5.5. Controlled oxidation of the hybrid generated oxidized functional groups, as -OH and -COOH, and promoted the transformation of hercynite to hematite. Due to the high dispersibility of the hybrid in water, it presents an interesting potential as nanofiller for hydrophilic polymers. © 2013 Elsevier Ltd. All rights reserved. Source

Mansilla M.A.,CONICET | Mansilla M.A.,Laboratorio Of Polimeros Y Materiales Compuestos | Marzocca A.J.,Laboratorio Of Polimeros Y Materiales Compuestos | Macchi C.,CONICET | Somoza A.,CONICET
European Polymer Journal | Year: 2015

Blends of natural rubber and styrene-butadiene rubber were prepared by solution mixing and vulcanized with a system sulfur-accelerator at 433 K and 443 K in order to study the vulcanization kinetic and the influence of the vulcanization temperature on the final structure of the blends. The kinetic of vulcanization was analyzed under the frame of the Han's model, which takes into account the reversion effect once the time to achieve the maximum torque in the rheometer curves is surpassed. The crosslink density was also determined in all samples by means of swelling in solvent. The average free nanohole volume was estimated using positron annihilation lifetime spectroscopy. When changing the vulcanization temperature of the blends, remarkable changes in the crosslink densities and the free nanohole volumes were detected. Furthermore, a correlation between the average fractional free nanohole volume and the fraction of polymer in the swollen state was established. © 2015 Elsevier Ltd. All rights reserved. Source

Garcia N.L.,Laboratorio Of Polimeros Y Materiales Compuestos | Garcia N.L.,National University of San Martin of Argentina | Ribba L.,Laboratorio Of Polimeros Y Materiales Compuestos | Dufresne A.,Grenoble Institute of Technology | And 2 more authors.
Carbohydrate Polymers | Year: 2011

Fully bio-based nanocomposites were prepared using starch nanoparticles obtained by acidic hydrolysis of waxy maize starch granules as reinforcement. The same type of starch, which contains 99 wt.% amylopectin, was used to prepare glycerol plasticized and unplasticized matrices. The X-ray diffraction pattern of the plasticized reinforced materials displays both A and B-type peaks, showing that the crystalline structure of the nanocrystals was not affected by processing. The storage modulus of the composite material increases, with respect to the unfilled film, by 470% at 50 °C, while the permeability increases by 70%. This is probably due to a good association of glycerol with the nanoparticles leading to a fibrillar structure, studied by scanning electron microscopy of plasticized and unplasticized composites. © 2010 Elsevier Ltd. All rights reserved. Source

Morales N.J.,CONICET | Morales N.J.,Laboratorio Of Polimeros Y Materiales Compuestos | Candal R.,CONICET | Candal R.,National University of San Martin of Argentina | And 4 more authors.
Carbohydrate Polymers | Year: 2015

Plasticized cassava starch matrix composites reinforced by a multi-wall carbon nanotube (MWCNT)-hercynite (FeAl2O4) nanomaterial were developed. The hybrid nanomaterial consists of FeAl2O4 nanoparticles anchored strongly to the surface of the MWCNT. This nano-hybrid filler shows an irregular geometry, which provides a strong mechanical interlocking with the matrix, and excellent stability in water, ensuring a good dispersion in the starch matrix. The composite containing 0.04 wt.% of the nano-hybrid filler displays increments of 370% in the Young's modulus, 138% in tensile strength and 350% in tensile toughness and a 70% decrease in water vapor permeability relative to the matrix material. All of these significant improvements are explained in terms of the nano-hybrid filler homogenous dispersion and its high affinity with both plasticizers, glycerol and water, which induces crystallization without deterioration of the tensile toughness. © 2015 Elsevier Ltd. All rights reserved. Source

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