Search results for "materiales"
showing 10 items of 204 documents
Curvature as a Guiding Field for Patterns in Thin Block Copolymer Films
2018
Experimental data on thin films of cylinder-forming block copolymers (BC)—free-standing BCmembranes as well as supported BC films—strongly suggest that the local orientation of the BC patternsis coupled to the geometry in which the patterns are embedded. We analyze this phenomenon using generalsymmetry considerations and numerical self-consistent field studies of curved BC films in cylindricalgeometry. The stability of the films against curvature-induced dewetting is also analyzed. In goodagreement with experiments, we find that the BC cylinders tend to align along the direction of curvature athigh curvatures. At low curvatures, we identify a transition from perpendicular to parallel alignm…
Diffusivity and free anion concentration of ionic liquid composite polybenzimidazole membranes.
2021
[EN] In this article, PBI composite membranes containing the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-NTf2) at 1, 5, 10, 20 and 50 wt% (named PBI-IL-x) have been prepared by a casting method. The internal morphology of the membranes was analyzed by scanning electron microscopy (SEM), revealing that the incorporation of IL promotes the formation of porous channels. Thermal and mechanical stability was confirmed by thermogravimetric analysis (TGA) and tensile test measurements. The ionic transport through membranes was analysed by means of electrochemical impedance spectroscopy (EIS), showing a dependence on the IL loading, reaching a highest condu…
Enhanced Conductivity of Composite Membranes Based on Sulfonated Poly(Ether Ether Ketone) (SPEEK) with Zeolitic Imidazolate Frameworks (ZIFs)
2018
The zeolitic imidazolate frameworks (ZIFs) ZIF-8, ZIF-67, and a Zn/Co bimetallic mixture (ZMix) were synthesized and used as fillers in the preparation of composite sulfonated poly(ether ether ketone) (SPEEK) membranes. The presence of the ZIFs in the polymeric matrix enhanced proton transport relative to that observed for SPEEK or ZIFs alone. The real and imaginary parts of the complex conductivity were obtained by electrochemical impedance spectroscopy (EIS), and the temperature and frequency dependence of the real part of the conductivity were analyzed. The results at different temperatures show that the direct current (dc) conductivity was three orders of magnitude higher for composite …
Colloids of naked CH 3 NH 3 PbBr 3 Perovskite Nanoparticles: Synthesis, Ssability, and thin solid film deposition
2018
A novel preparation of lead halide, CH3NH3PbBr3, perovskite nanoparticle solid films from colloidal "naked" nanoparticles, that is, dispersible nanoparticles without any surfactant, is reported. The colloids are obtained by simply adding potassium ions, whose counterions are both more lipophilic and less coordinating than bromide ions, to the perovskite precursor solutions (CH3NH3Br/PbBr2 in dimethylformamide) following the reprecipitation strategy. The naked nanoparticles exhibit a low tendency to aggregate in solution, and they effectively self-assembled on a substrate by centrifugation of the colloid, leading to homogeneous nanoparticle solid films with arbitrary thickness. These results…
High pressure in-situ X-ray diffraction study on Zn-doped magnetite nanoparticles
2018
We have performed high pressure synchrotron X-ray powder diffraction experiments on two different samples of Zn-doped magnetite nanoparticles (formula Fe(3-x)ZnxO4; x = 0.2, 0.5). The structural behavior of then a noparticles was studied up to 13.5 GPa for x = 0.2, and up to 17.4 GPa for x = 0.5. We have found that both systems remain in the cubic spinel structure as expected for this range of applied pressures. The analysis of the unit cell volume vs. pressure results in bulk modulus values lower than in both end-members, magnetite (Fe3O4) and zinc ferrite (ZnFe2O4), suggesting that chemical disorder may favor compressibility, which is expected to improve the increase of the Neel temperatu…
Current-induced fingering instability in magnetic domain walls
2015
The shape instability of magnetic domain walls under current is investigated in a ferromagnetic (Ga,Mn)(As,P) film with perpendicular anisotropy. Domain wall motion is driven by the spin transfer torque mechanism. A current density gradient is found either to stabilize domains with walls perpendicular to current lines or to produce finger-like patterns, depending on the domain wall motion direction. The instability mechanism is shown to result from the non-adiabatic contribution of the spin transfer torque mechanism.
Comparative In Vitro Study of the Bond Strength of Composite to Carbon Fiber Versus Ceramic to Cobalt–Chromium Alloys Frameworks for Fixed Dental Pro…
2020
Purpose: The aim of this comparative in vitro study was to assess the bond strength and mechanical failure of carbon-fiber-reinforced composites against cobalt&ndash
Effective antimicrobial materials based on low-density polyethylene (LDPE) with zinc oxide (ZnO) nanoparticles
2019
[EN] Effective antimicrobial polymeric nanocomposites were prepared with low density polyethylene (LDPE) and zinc oxide nanoparticles by melt compounding. These nanoparticles (~17 nm) obtained by the sol¿gel method, were used both as-synthesized and modified organically with oleic acid (Mod-ZnO). Young¿s modulus increased ~15 and 18% for LDPE/ZnO and LDPE/Mod-ZnO, respectively, compared to neat LDPE. When these composites were irradiated with white light, they showed an increase with nanoparticle incorporation, and the antimicrobial properties against E. coli were ~96¿99%. The release of the Zn cations was related to the antimicrobial properties. These nanocomposites are attractive for use …
Nanorings and rods interconnected by self-assembly mimicking an artificial network of neurons
2013
[EN] Molecular electronics based on structures ordered as neural networks emerges as the next evolutionary milestone in the construction of nanodevices with unprecedented applications. However, the straightforward formation of geometrically defined and interconnected nanostructures is crucial for the production of electronic circuitry nanoequivalents. Here we report on the molecularly fine-tuned self-assembly of tetrakis-Schiff base compounds into nanosized rings interconnected by unusually large nanorods providing a set of connections that mimic a biological network of neurons. The networks are produced through self-assembly resulting from the molecular conformation and noncovalent intermo…
Defect spectroscopy of single ZnO microwires
2014
The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 1018 cm3 . This combination of tech…