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Vega-Baudrit J.,National University of Costa Rica | Vega-Baudrit J.,Laboratorio Nacional Of Nanotecnologia | Delgado-Montero K.,National University of Costa Rica | Madrigal-Carballo S.,National University of Costa Rica
Cellulose Chemistry and Technology | Year: 2011

In a previous work, it was demonstrated that 70% of the molasses isolated from the biowaste generated by the agro-industrialization of sugar cane allow obtaining composite materials with adequate mechanical properties and bulk density. In the present research, these results were applied in the preparation of composite polyurethanes based on sugar cane molasses reinforced with bagasse fiber from the same biowaste. Initially, milled fibers from bagasse were characterized both physically and chemically, according to their content of a-cellulose, moisture, ashes, hemicelluloses and lignin, as well as to their extractability in organic and aqueous solvents. The most representative values were a-cellulose (47.3%), lignin (24.4%) and holocellulose(66.1%). Subsequently, polyurethane foams (PUF) were prepared using the natural fiber as a reinforcement, with 4 different percentages of fiber ground (5, 10, 15, 20% w/w) with an average particle size of 60 mesh; an extra PUF without fiber reinforcement was also synthesized as a reference. PUF synthesis was carried out with a PEG-molasses mixture in a 30:70% (w/w) ratio, diphenylmethane diisocyanate (MDI) and dibutyltin dilaurate as catalysts. Composite PUFs were characterized according to their bulk density, thermal (thermogravimetry-TGA) and mechanical (compression modulus) properties. The results showed that the composite PUF sample with 10% sugar cane fiber added as reinforcement had the lowest bulk density. Also, its TGA thermal analysis showed a general trend towards reducing both the initial temperature of decomposition, as well as the temperature at the maximum rate of degradation, compared to the reference PUF without fiber added. Finally, its mechanical properties showed a maximum value for both effort to compression and compression modulus. It has been concluded that the use of agro-industrial biowaste from sugar cane permits to develop composite materials with suitable properties for applications as foams. The PUF synthesized by partial replacement of PEG for molasses and reinforced with sugar cane bagasse fiber can be used in the packaging industry. In this case, the materials are used for short periods, and are usually very bulky, less dense. Thus, this novel type of PU foam could be useful in reducing the production costs and in improving the potential biodegradability of the polymeric matrix, becoming an interesting value-added application for this important source of agricultural biowastes, especially in Latin America. Source

Zagonel L.F.,Laboratorio Nacional Of Nanotecnologia | Zagonel L.F.,University Paris - Sud | Rigutti L.,University Paris - Sud | Rigutti L.,CNRS Material Physics Group | And 4 more authors.
Nanotechnology | Year: 2012

The optical properties of a stack of GaN/AlN quantum discs (QDiscs) in a GaN nanowire have been studied by spatially resolved cathodoluminescence (CL) at the nanoscale (nanoCL) using a scanning transmission electron microscope (STEM) operating in spectrum imaging mode. For the electron beam excitation in the QDisc region, the luminescence signal is highly localized, with spatial extent as low as 5nm, due to the high band gap difference between GaN and AlN. This allows the discrimination between the emission of neighbouring QDiscs and evidencing the presence of lateral inclusions, about 3nm thick and 20nm long rods (quantum rods, QRods), grown unintentionally on the nanowire sidewalls. These structures, also observed by STEM dark-field imaging, are proved to be optically active in nanoCL, emitting at similar, but usually shorter, wavelengths with respect to most QDiscs. © 2012 IOP Publishing Ltd. Source

Oiko V.T.A.,University of Campinas | Martins B.V.C.,University of Alberta | Silva P.C.,Laboratorio Nacional Of Nanotecnologia | Rodrigues V.,University of Campinas | Ugarte D.,University of Campinas
Review of Scientific Instruments | Year: 2014

Understanding the mechanical properties of nanoscale systems requires new experimental and theoretical tools. In particular, force sensors compatible with nanomechanical testing experiments and with sensitivity in the nN range are required. Here, we report the development and testing of a tuning-fork-based force sensor for in situ nanomanipulation experiments inside a scanning electron microscope. The sensor uses a very simple design for the electronics and it allows the direct and quantitative force measurement in the 1-100 nN force range. The sensor response is initially calibrated against a nN range force standard, as, for example, a calibrated Atomic Force Microscopy cantilever; subsequently, applied force values can be directly derived using only the electric signals generated by the tuning fork. Using a homemade nanomanipulator, the quantitative force sensor has been used to analyze the mechanical deformation of multi-walled carbon nanotube bundles, where we analyzed forces in the 5-40 nN range, measured with an error bar of a few nN. © 2014 AIP Publishing LLC. Source

Pitthan E.,Federal University of Rio Grande do Sul | Gobbi A.L.,Laboratorio Nacional Of Nanotecnologia | Stedile F.C.,Federal University of Rio Grande do Sul
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2016

Phosphorus detection and quantification were obtained, using the 31P(α,p)34S nuclear reaction and Rutherford Backscattering Spectrometry, in deposited silicon oxide films containing phosphorus and in carbon substrates implanted with phosphorus. It was possible to determine the total amount of phosphorus using the resonance at 3.640 MeV of the 31P(α,p)34S nuclear reaction in samples with phosphorus present in up to 23 nm depth. Phosphorous amounts as low as 4 × 1014 cm-2 were detected. Results obtained by nuclear reaction were in good agreement with those from RBS measurements. Possible applications of phosphorus deposition routes used in this work are discussed. © 2015 Elsevier B.V. All rights reserved. Source

Solovev A.A.,Leibniz Institute for Solid State and Materials Research | Xi W.,Leibniz Institute for Solid State and Materials Research | Gracias D.H.,Leibniz Institute for Solid State and Materials Research | Gracias D.H.,Johns Hopkins University | And 6 more authors.
ACS Nano | Year: 2012

We describe nanoscale tools in the form of autonomous and remotely guided catalytically self-propelled InGaAs/GaAs/(Cr)Pt tubes. These rolled-up tubes with diameters in the range of 280-600 nm move in hydrogen peroxide solutions with speeds as high as 180 μm s -1. The effective transfer of chemical energy to translational motion has allowed these tubes to perform useful tasks such as transport of cargo. Furthermore, we observed that, while cylindrically rolled-up tubes move in a straight line, asymmetrically rolled-up tubes move in a corkscrew-like trajectory, allowing these tubes to drill and embed themselves into biomaterials. Our observations suggest that shape and asymmetry can be utilized to direct the motion of catalytic nanotubes and enable mechanized functions at the nanoscale. © 2012 American Chemical Society. Source

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