Mariano Romero

The effect of manganite nanoparticle addition on the low field magnetoresistance of polyaniline

In this report, we studied the effect of the addition of manganite nanoparticles on the microstructure and magnetotransport properties of polyaniline polymers. We showed experimental results on the fractal dimension of the polyaniline–manganite nanocomposites by means of small angle X-ray scattering measurements. A decrease in the number of polarons is observed for the composite with a concentration of 20% manganite nanoparticles. On the other hand, for the same concentration, the presence of a low magnetic field increases the number of polarons, in relation to an enhancement of the negative low field magnetoresistance (LFMR). This enhancement was observed for a critical amount of manganite nanoparticle addition in the whole temperature regime analyzed, as envisaged from the low magnetic field dependence in the polyaniline polaron formation observed using confocal Raman spectroscopy at room temperature.

Experimental and Theoretical Study of Ionic Pair Dissociation in a Lithium Ion–Linear Polyethylenimine–Polyacrylonitrile Blend for Solid Polymer Electrolytes

Herein, we report the preparation and characterization of a novel polymeric blend between linear polyethylene imine (PEI) and polyacrylonitrile (PAN), with the purpose of facilitating the dissociation of lithium perchlorate salt (LiClO4) and thus to enhance Li ion transport. It is a joint theoretical and experimental procedure for evaluating and thus demonstrating the lithium salt dissociation. The procedure implies the correlation between the theoretical pair distribution function (PDF) and conventional X-ray diffraction (XRD) by means of a molecular dynamics (MD) approach. Additionally, we correlated the experimental and theoretical Raman and infrared spectroscopy for vibrational characterization of the lithium salt after dissociation in the polymeric blend. We also performed confocal Raman microscopy analysis to evidence the homogeneity on the distribution of all components and the LiClO4 dissociation in the polymer blend. The electrochemical impedance analysis confirmed that the Li-PAN-PEI blend presents a slightly better lithium conductivity of ∼8 × 10-7 S cm-1. These results suggest that this polymer blend material is promising for the development of novel fluorine-free solid polymer lithium ion electrolytes, and the methodology is suitable for characterizing similar polymeric systems.

Novel fluorine-free 2,2′-bis(4,5-dimethylimidazole) additive for lithium-ion poly(methyl methacrylate) solid polymer electrolytes

In this report, we study the effect of the addition of fluorine-free 2,2′-bis(4,5-dimethylimidazole) (BDI) on lithium-ion solid polymer electrolytes based on lithium nitrate and poly(methyl methacrylate) (PMMA). Confocal Raman spectroscopy and theoretical Raman calculations were performed to study lithium dissociation and the interaction mechanism of the lithium and nitrate ions with the BDI additive. Additionally, X-ray diffraction analysis showed that the mean coherence length of the PMMA chains is influenced by the BDI concentration. The incorporation of the BDI additive favors the dissociation of lithium salt leading to a maximum enhancement on the lithium conductivity of up to 1.88 × 10−4 S cm−1 for a critical BDI addition of ∼5% with respect to PMMA, which is very high in comparison with the conductivities of ∼10−4 S cm−1 usually observed for these solid polymer electrolytes.

Raman Microscopy Insights on the Out-of-Plane Electrical Transport of Carbon Nanotube-Doped PEDOT:PSS Electrodes for Solar Cell Applications

In the present report, we focused on the study of the out-of-plane electrical transport of multiwalled carbon nanotube (MWCNT)-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) composites (PEDOT:PSS-MWCNTs) as electrodes for solar cell applications. The out-of-plane direct current and alternating current electrical transport, rarely studied but not less relevant, was additionally supported with in-plane and out-of-plane confocal Raman microscopy and grazing incidence small-angle X-ray scattering characterizations. The main relevance of our study is the monitoring of the polymer structure all across the polymeric film by using confocal Raman spectroscopy and its correlation with electrical transport. Modifications in the PEDOT benzenoid and quinoid conformations were observed in the vicinities of MWCNTs, and the enrichment of PSS at the indium tin oxide electrode interface was also evidenced. In consequence, the low MWCNT loadings into PEDOT:PSS lead to an increase of the out-of-plane conductivity, but the heavier MWCNT loadings lead to a drastic decrease. The tuning of the doping level of these polymer composites and the understanding of the interface structure are crucial to fabricate electrodes with higher out-of-plane conductivities for organic solar cell applications.

The structural and organic magnetoresistance response of poly(9-vinyl carbazole) using low applied magnetic fields and magnetic nanoparticle addition

Herein, we report the tuning of the structural and organic magnetoresistance response of poly(9-vinyl carbazole) (PVK) with magnetic nanoparticle addition under exposure to low applied magnetic fields. X-ray diffraction analysis showed evidence of PVK conformational changes by either adding magnetic nanoparticles or by applying an external magnetic field. Molecular dynamics simulations suggested that the loss of aromaticity could lead to slight but detectable modifications in the PVK structure. Confocal Raman spectroscopy under low applied magnetic field evidenced modifications in PVK singlet and triplet populations followed by theoretical simulation to assign the vibrational modes in PVK different multiplicities. Both the addition of magnetic nanoparticles and the presence of an applied magnetic field showed an increase in the PVK triplet-to-singlet ratio. PVK nanocomposites showed negative low field magnetoresistance (MR) reaching maximum values of MR (2 kOe) = −1.1 and −9.0% for T = 280 and 20 K, respectively. The MR dependence with low applied magnetic fields showed a typical behavior in agreement with the electron–hole recombination mechanism. This latter effect could be experimentally associated with the change in the PVK triplet-to-singlet ratio, as observed by Raman analysis. In addition, the PVK magnetoresistance effect could also be ascribed to conformational changes induced by the presence of magnetic nanoparticles and an applied magnetic field, as evidenced by X-ray diffraction analysis.

Development and Characterization of Vitamin A-Loaded Solid Lipid Nanoparticles for Topical Application

Vitamin A and its esters are commonly found in topical applications because of their advantageous properties, however, have the drawback that are highly sensitive to ultraviolet radiation. The aim of this work was to develop and characterize a novel formulation of solid lipid nanoparticles suitable for topical applications in order to protect vitamin A from degradation. Vitamin A-loaded nanoparticles were successfully prepared by hot homogenization employing Gelucire 44/14 and cetyl alcohol as carrier materials, showing an entrapment efficiency of more than 90%. Particle size, measured by dynamic light scattering, was ca. 40 nm, while transmission electron microscopy images showed that dried nanoparticles were spherical with an average size of about 30-50 nm. Small angle X-ray scattering was used to study their aspect ratio and their physicochemical properties were evaluated by differential scanning calorimetry, infrared spectroscopy and X-ray powder diffraction, additionally, stability of vitamin A was studied by UV-Vis spectroscopy.

From positive to negative magnetoresistance behavior at low applied magnetic fields for polyaniline:titania quantum dot nanocomposites

Here, we report the tuning from the positive to negative magnetoresistance response at room temperature and low applied magnetic fields (H ∼ 200 mT) for polyaniline nancomposites prepared via in situ growth of titanium oxide quantum dots. In addition, we showed experimental Raman evidence revealing that the positive magnetoresistance response in these polyaniline nanocomposites is mediated by the bipolaron mechanism. Confocal Raman spectroscopy under applied magnetic field analysis showed the decrease of the polaron population to form bipolarons of polyaniline when exposed to an applied magnetic field for the TiO2 quantum dot diluted regime. Negative magnetoresistance, observed for the TiO2 quantum dot higher concentration regime, was attributed to the suppression of polyaniline polarons probably associated with its partial chemical functionalization at the interface due to the increasing concentration of TiO2 quantum dots.Here, we report the tuning from the positive to negative magnetoresistance response at room temperature and low applied magnetic fields (H ∼ 200 mT) for polyaniline nancomposites prepared via in situ growth of titanium oxide quantum dots. In addition, we showed experimental Raman evidence revealing that the positive magnetoresistance response in these polyaniline nanocomposites is mediated by the bipolaron mechanism. Confocal Raman spectroscopy under applied magnetic field analysis showed the decrease of the polaron population to form bipolarons of polyaniline when exposed to an applied magnetic field for the TiO2 quantum dot diluted regime. Negative magnetoresistance, observed for the TiO2 quantum dot higher concentration regime, was attributed to the suppression of polyaniline polarons probably associated with its partial chemical functionalization at the interface due to the increasing concentration of TiO2 quantum dots.

X Ray Diffraction: An Approach to Structural Quality of Biological Preserved Tissues in Tissue Banks

Cryopreservation techniques are fundamental supports in the conservation procedures of biological materials in TB work. However, controversial views remain on the effects at the molecular level that cryogenic temperatures and thawing could produce on the functional structures of tissues. The same concept can be sustained to glycerolized tissue preservation. Taking into account this scope, we implemented a methodological scheme to analyze tissue specimens before and after programmed cryopreservation, or glycerolization in order to find structural differences in the basic material constitutive collagen, using the techniques formerly mentioned: diffractive and scattering.