A. Manzano-Ramírez

Molecular dynamics analysis of PVA- AgnP composites by dielectric spectroscopy

The molecular dynamics of PVA/AgnP composites were studied by dielectric spectroscopy (DS) in the 20-300°C temperature range. Improper water elimination leads to misinterpretation of thermal relaxations in PVA composites in agreement with the previous report for pristine PVA. The evaporation of water and its plasticizing effect are more evident in pure PVA confirming the existence of strong interaction between OH groups of PVA chains and AgnP. Dry films show a single nonlinear VFT dependence (from 45°C until melting) associated to the α-relaxation and, therefore, to the glass transition phenomenon and from dielectric measurements, the Tg of composites vary from 88*deg;C for pristine PVA to 125°C for PVA/AgnP (5wt%). Below 45°C, dry films exhibit a single Arrhenius behavior showing a 3D hopping conductivity as explained based on the variable range hopping model. PVA/AgnP composites have higher conductivity compared to pristine PVA, and it increases as AgnP weight percent increases. Finally, DMA measurements support the statement that a secondary relaxation was erroneously assigned as the glass transition of PVA and composites in previous reports.

A review on the efficiency of graphene-based BHJ organic solar cells

Graphene, a material composed of one-atom-thick planar sheets of sp2-bonded carbon atoms with a two-dimensional honeycomb structure, has been proposed for many applications due to its remarkable electronic, optical, thermal, and mechanical properties. Its high transparency, conductivity, flexibility, and abundance make it an excellent material to be applied in the field of organic photovoltaic cells, especially as a replacement for transparent conducting oxide electrodes. However, graphene has been demonstrated to be useful not only as substitute for indium tin oxide electrodes, but also as cathode, electron acceptor, hole transport, and electron extraction material. Thus, in this work, we summarize and discuss the efficiency of bulk heterojunction devices using graphene as a main constituent.

Exergetic and Thermoeconomic Analyses of Solar Air Heating Processes Using a Parabolic Trough Collector

This paper presents a theoretical and practical analysis of the application of the thermoeconomic method. A furnace for heating air is evaluated using the methodology. The furnace works with solar energy, received from a parabolic trough collector and with electricity supplied by an electric power utility. The methodology evaluates the process by the first and second law of thermodynamics as the first step then the cost analysis is applied for getting the thermoeconomic cost. For this study, the climatic conditions of the city of Queretaro (Mexico) are considered. Two periods were taken into account: from July 2006 to June 2007 and on 6 January 2011. The prototype, located at CICATA-IPN, Qro, was analyzed in two different scenarios i.e., with 100% of electricity and 100% of solar energy. The results showed that thermoeconomic costs for the heating process with electricity, inside the chamber, are less than those using solar heating. This may be ascribed to the high cost of the materials, fittings, and manufacturing of the solar equipment. Also, the influence of the mass flow, aperture area, length and diameter of the receiver of the solar prototype is a parameter for increasing the efficiency of the prototype in addition to the price of manufacturing. The optimum design parameters are: length is 3 to 5 m, mass flow rate is 0.03 kg/s, diameter of the receiver is around 10 to 30 mm and aperture area is 3 m2.

Improved structural properties of SiO2 sol-gel films

Silicon oxide films with a small amount of alpha alumina particles embedded in the glass matrix were prepared using the sol-gel method. It is found that the structural properties of these samples are superior to those observed in similarly prepared films, but without the alumina particles. This conclusion was deduced from analysis of the oxygen diffusion measurements through the SiO2 layer, using a novel method, and from the measured dielectric breakdown field. It is found that the oxygen diffusion coefficient is much lower and the dielectric breakdown field is larger in samples with the alumina particles.

Surface Enhanced Raman Scattering of graphite on metals

Surface Enhanced Raman Scattering of graphite deposited on Al, Cu and Fe surface has been observed. Ultrathin layers of graphite consisting of only a few carbon monolayers were deposited using a chemical method. Comparing the graphite Raman intensity from these ultrathin layers with those obtained in thicker carbon samples on glass substrates deposited using the sputtering method, the enhancement intensity factor has been determined.

The potential use of geopolymer for cleaning air

Abstract Geopolymers are aluminosilicates structures used for different applications, most of them for construction and cementitious materials. Recently, they have been used as support for optical applications, color holder, color pH indicator, fluorescent materials, and for volatile organic degradation by photocatalysis for instance. Three geopolymers were synthesized at different temperatures. Optical characterization of each one was performed to assess the amount of light transmitted, absorbed, and remitted. They were ion exchanged to incorporate TiO2 and their photoactivity was measured by fluorescence. Changes of the geopolymers structure were followed by Transmission Electron Microscope (TEM) and specific surface by Barret-Joyner-Halenda method (BJH). According to the obtained results, a sample at one single temperature was chosen to assess its performance under controlled conditions. To do this, a batch reactor was built and the Langmuir-Hinshelwood model was used to explain the adsorption of reactants on the geopolymer surface. Finally, reaction products were analyzed by gas chromatography and the phenomena was explained.

Morphology Effect of Silver Nanostructures on the Performance of a P3HT

We report the effect of the use of different silver nanostructures (AgNs) layers deposited via dip coating onto a poly(3-hexylthiophene) (P3HT) and solution processable functionalized graphene (SPFGraphene) composite film intended to be used as active layer in BHJ devices. SPFGraphene was added to P3HT in a ratio of 1.5źwt%. The best results were achieved when a layer of silver nano-pseudospheres (AgNPSs) obtained after 10 immersion cycles was used as coating; in this case the highest light trapping and efficiency percent (ź=0.23%) were achieved. This means an increase of ~11.3% in comparison with the efficiency of the noncoated P3HT:SPFGraphene composite. Results also indicate that graphene was successfully functionalized in order to obtain appropriate dispersion in P3HT and that such conjugated polymer remained unaltered after the addition of SPFGraphene. Finally, it can be concluded that the electrical properties of the as-synthesized films are dependent on the shape and concentration of the AgNs deposited via dip coating.

Comparative Study on the Effect that Coir Fibers Have on the Dynamic or Quasi-Static Elastic Moduli of Glass Fiber Laminates Obtained by the Vacuum Bag Technique

The use of natural fibers has a great interest due to their damping properties, low density and moderate strength. The effect of incorporating chopped natural fibers, as disperse reinforced phase, on the dynamic or quasi-static elastic modulus of glass fiber laminates is presented. Squares of 32 cm2 plain wave glass fiber prepreg with epoxy resin were used in a stacking sequence [0]4. Short length chopped (1-3 mm) natural coir fiber was placed in between of each glass fiber prepreg sheet (4) and laminates were prepared by the vacuum bag technique. The volume fraction of natural fiber was 30% (mass fraction of 10%) and samples of 254 mm length and 25.4 mm width were cut and tested at vibration conditions in a cantilever beam arrangement. The vibration frequency was measured by an accelerometer ADXL335 at z-axis, perpendicular to the sample test plane and the elastic modulus was estimated with the cantilever model. The results showed that the samples with coir fiber showed an increase in the dynamic elastic modulus value of 150 to 171% with regard to that one of glass fiber samples without fiber. Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials (ASTM D3039) was also used to further characterize the thin samples (≈0.75 mm) with an Instron machine 8800, 25kN. The tensile properties obtained are lower for coir fiber samples than the ones without.

Study on the Pozzolanic Effect of Sugarcane Bagasse Ash from Taretan, Michoacán, Mexico, on a Portland Cement Mortar

Since the construction industry is responsible for 30% of the CO2 emissions, one way to reduce the impact of the construction activity is to substitute ordinary Portland cement by pozzolanic materials. The application of using agricultural waste in the production of pozzolanic material is technically feasible, due to the calcination of organic materials and leaving ashes with a fine particle size and high SiO2 content. In the present, it is discussed the pozzolanic effect of sugarcane bagasse ash (SCBA) from Taretan, Michoacán, Mexico, on the physical and mechanical properties of a portland cement mortar. Test specimens were prepared based on replacing sugarcane bagasse ash percentages of 5, 10, 15, 20 and 30 %, relative to the weight of cement. To validate the mechanical properties of the specimens, tensile, flexural and compressive strength was determine. The porosity of the mortar was determined by means of non-destructive ultrasonic testing of pulse rate and electrical resistivity. The contribution of this paper was determine the bond strength of an overlay mortar with SCBA bonded to the concrete substrate by pull-out tests. The results showed that the addition of the sugarcane bagasse ash improved the mechanical strength, adherence of the mortar to concrete, and decreases the porosity on large curing times. Hence, it is suggested the use of Portland pozzolan cement containing sugarcane bagasse ash pozzolan, with the added benefit on the use of agricultural waste.

Tensile and Flexural Strength of Untreated Woven Henequen-Glass Fabric Reinforced Epoxy Hybrid Composites

The use of eco-friendly composites has gained attraction due to its lightweight and moderate strength in recent years. The aim of this paper was to study the influence of the stacking sequence of glass and henequen fabrics on the mechanical properties of epoxy composites. Fiber/Matrix interface adhesion was examined using SEM. It was observed how the tensile and flexural properties of the hybrid reinforced epoxy laminates with henequen and glass fabrics, increase as the number of layers of henequen woven fabric decrease while stacking sequence does not have a great effect on the tensile properties. However, when ten layers of henequen fabric were used, a eco-friendly composite material with good mechanical strength was obtained due to the mechanical anchoring of the henequen fabric with the epoxy resin. Hence, it is clearly shown how by tailoring the geometry of the fabric, improvements in the mechanical properties of eco-friendly polymer composites can be achieved.