Thickness effect on the solvent sensing parameters of carbon black-polymer composites

investigación realizada en proyecto de Red TemáticaStudy of the sensing parameters: sensibility, response and recuperation times to hexane vapors for layers of different thickness of poly(butadiene) + carbon black (CB) composites is presented. The results show that sensibility increases as the CB- weight percent diminishes, being in agreement with reported results by several researches. In this work another variable was studied on the sensing parameters, the thickness. The initial electrical resistance of the studied layers increases until three magnitude orders as diminish theirs thickness and the sensibility in this study increases until one magnitude order as the layer thickness diminishes around 0.25 μm.Programa de Mejoramiento al Profesorado (PROMEP, México), proyecto de red PROMEP 2013-2014

Synthesis and Characterization of Polyaniline/Magnetite Nanocomposite

trabajo de investigación de Red TemáticaA conducting-electroactive polyaniline/magnetite (PAni/Fe304) nanocomposite was synthesized using anilinium dodecylbenzene sulfonate (S1) as a reactive surfactant. First, S1 allowed magnetite dispersion in the aqueous phase and second, S1 performed as the monomer of polyaniline emeraldine base salt. Electron microscopy suggested core-shell morphology based on S1 amphiphilic character; that is, S1 adsorbed onto the magnetite nanoparticles surface and then was polymerized via an oxidative polymerization forming the shell. The PAni/Fe304 composite exhibited improved thermal stability regarding pure PAni, which was related to the strong interaction between PAni and magnetite. Electrical conductivity, determined by the four-probe method, was in the order of 10-1 and 10-3 S cm-1, respectively, for the pure PAni and the composite. Concerning composite magnetic properties, the decrement in magnetization (σr) and hysteresis (Hc) was attributed to the increment in dipolar magnetic interaction due to the increased separation among magnetite nanoparticles because of the PAni shell.PROMEP-SEP, Programa: Redes Temáticas de Colaboración Académica, "Red de Compuestos Poliméricos, Propiedades y Aplicacione

Effect of size and composition on the second harmonic generation from lithium niobate powders at different excitation wavelengths

INVESTIGACIÓN DESARROLLADA EN COLABORACIÓN DE RED TEMATICA PRODEP /SEP/MEXICOLiNbO3 microcrystalline systems, possessing almost stoichiometric composition, were produced by varying the temperature and time parameters in the annealing processes following a mechanochemical reaction of raw powders. SHG from these samples, detected for every fundamental wavelength in the range 800-1300 nm, and being maximal at a certain wavelength, λmax, for each sample, has been addressed to a random scattering of the induced nonlinear polarizations. Possible tuning of λmax could be ascribed to control of composition and grain size of the sample. Random orientation of the produced nanocrystallites was verified since no dependence for SHG intensity on incident polarization was observed.PAPIIT-UNAM through grant IN117116 Y “RED PRODEP-SEP Compuestos poliméricos propiedades y aplicaciones 2015-2016

Optical properties of carbon nanostructures produced by laser irradiation on chemically modified multi-walledcarbon nanotubes

Apoyo a la Red Temática de Colaboración Académica: Desarrollo de Materiales Compuestos con propiedades Ópticas, Eléctricas , Magnéticas y sus aplicacionesThis research focused on the nanosecond(Nd:YAG-1064 nm) laser pulse effect on the optical and morphological properties of chemically modified multi-walled carbon nanotubes(MWCNT).Two sus- pensions of MWCNT in tetrahydrofuran (THF) were prepared,one was submitted to laser pulses for 10 min while the other (blank) was only mechanically homogenized during the same time. Following the laser irradiation, the suspension acquired a yellow-amber color,in contrast to the black translucent appearance of the blank. UV-vis spectroscopy confirmed this observation, showing the blank a higher absorption. Additionally, photoluminescence measurements exhibited a broad blue-green emission band both in the blank and irradiated suspension when excited at 369 nm, showing the blank a lower intensity. However, a modification in the excitation wave length produced a violet to green tuningin the irradiated suspension, which did not occurin the blank. Lastly, the electron microscopy analysis of the treated nanotubes showed the abundant formation of amorphous carbon, nanocages, and nanotube unzipping, exhibiting the intense surface modification produced by the laser pulse. Nanotube surface modification and the coexistence with the new carbon nanostructures were considered as the conductive conditions for optical properties modification.PROME

Synthesis by wet chemistry and characterization of LiNbO3 nanoparticles

Actually, lithium niobate (LiNbO3) has been used for optical wavelength conversion and ultrafast optical signal processing because of its outstanding rapid nonlinear optical response behavior, low switching power and broad conversion bandwidth. LiNbO3nanoparticles, which belong to the ferroelectric oxide class, were synthesized by chemical reaction with wetchemistry. Their sizedistributionwascenteredaround200 nm. Xray diffraction (XRD) and scanning electron microscopy (SEM) were used to further investigate the quality of the obtained LiNbO3powders.The present work shows thatby employingthis chemical method the correct stoichiometric phasewas obtained. This wascorroborated by XPS (X-Ray Photoelectron Spectroscopy) results. Also, the nanoparticles showed a defined crystallinity and uniform morphology. This way of obtaining nanoparticles is innovative because of its low cost and simple way to reproduce it. It isan important method of increasing the surfacearea, controlling thephase purityand reducing theparticle size distribution. The samples were obtained under low temperature annealing at500, 650 and 800 ºC. Those features can be controlled using variables such temperature, time of synthesis,and calcination. In previous worksit wasfound that hydrothermal methods offer many advantages over conventional ceramic synthesis methods

Structural Aspects LiNbO3 Nanoparticles and Their Ferromagnetic Properties

We present a solid-state synthesis of ferromagnetic lithium niobate nanoparticles (LiNbO3) and their corresponding structural aspects. In order to investigate the effect of heat treatments, two batches of samples with a heat-treated (HT) and non-heat-treated (nHT) reduction at 650 °C in 5% of hydrogen/argon were considered to investigate the multiferroic properties and their corresponding structural aspects; using magnetometry and scanning transmission electron microscopy (STEM). Results indicate the existence of ferromagnetic domains with a magnetic moment per unit cell of 5.24 × 10−3 μB; caused mainly due to voids and defects on the nanoparticle surface, as confirmed by STEM measurements