Effect of Carbon Nanofiber Functionalization on the Dispersion and Physical and Mechanical Properties of Polystyrene Nanocomposites

Summary: The effect of peroxide functionalization of carbon nanofibers (CNF) on the physical and mechanical properties of polystyrene (PS)–CNF nanocomposites prepared via melt mixing was studied. The CNF functionalization was evidenced by Raman spectroscopy, comparing the ratio of peaks at 1 371 and at 1 590 cm^?1 (peaks related to the disordered sp³‐hybridized carbon atom and to the graphitic structure of the sp²‐hybridized carbon atoms, respectively). The variation of the storage (E′) and tensile modulus (E) of the PS–CNF composites as a function of the untreated and peroxide treated CNF concentration were evaluated. Three different peroxide concentrations were used for treating the CNF. It was found that both E′ and E increase with CNF concentration and, in addition, increase further with the peroxide treated CNFs. Nonetheless, it was found that the greater the peroxide concentration used in treating the CNF, the greater the PS degradation via free radical attack on the polymer chain, with the corresponding negative effect on the storage and tensile modulus. Dispersion of the CNF was assessed using scanning and optical microscopy, and the positive effect of the peroxide treatment on the dispersion of the CNF is evidenced.

Tensile stress‐strain behavior of PS/CNF nanocomposites.     

Monte Carlo Simulations for Tomlinson Sliding Models for Non-Sinusoidal Periodic Potentials

It is shown that the velocity dependence of a tungsten tip sliding against a mica surface cannot be fit to a semi-empirical analytical solution of the Tomlinson/Prandtl model using a simple sinusoidal sliding potential. This could be due to invalid assumptions in the model itself. However, if it is assumed that the periodic sliding potential is much sharper than a simple sinusoid, quantitative agreement between the experimental velocity dependence of the sliding force and theory is obtained using a single variable parameter, the height of the surface potential. Sliding is modeled in this case using Monte Carlo theory, and it is found that the height of the potential varies linearly with the normal load.     

Catalyst layer optimization by surface tension control during ink formulation of membrane electrode assemblies in proton exchange membrane fuel cell

A cost effective production of the membrane electrode assemblies (MEA) is a crucial issue for the generation of electricity by proton exchange membrane fuel cells (PEMFC). The deposition of the exact catalyst content on the electrodes in a single printing step is desirable to save processing time and enable cost reduction. In this study, an innovative MEA production process by screen print is developed to produce high performance catalyst layers. The control of the surface tension of the catalyst ink is fundamental to allow the catalyst layer deposition in a single printing step. The electrodes prepared in this way show higher performance than those prepared in several steps. The optimal ink developed shows a viscosity of 2.75 Pa s, a total solid content of 33.76 wt.%, a density of 1.294 g cm⁻³, and tack value of 92 U.T.     

Mass transfer in VOC adsorption on zeolite: experimental and theoretical breakthrough curves

From experimental results of adsorption of volatile organic compounds (VOCs) on zeolite, we propose simulations of the breakthrough curves based on the Linear Driving Force model. Experiments were run on fixed beds of hydrophobic commercial zeolites. Pollutants chosen are from several chemical classes with different polarities. A good agreement between experimental and numerical results is found when an adjustable value of the internal mass-transfer coefficient is used. A constant value of effective diffusivity is found independent of the nature and the amount of VOCs adsorbed. A relation linking intrapellet mass-transfer coefficient and equilibrium constant is proposed, including the average effective diffusivity, to make predictions of breakthrough curves for any kind of volatile organic pollutant in gaseous effluents.     

The Polar/Antipolar Phase Boundary of BiMnO3–BiFeO3–PbTiO3: Interplay among Crystal Structure,Point Defects,and Multiferroism

The ferromagnetic perovskite oxide BiMnO₃ is a highly topical material, and the solid solutions it forms with antiferromagnetic/ferroelectric BiFeO₃ and with ferroelectric PbTiO₃ result in distinctive polar/nonpolar morphotropic phase boundaries (MPBs). The exploitation of such a type of MPBs could be a novel approach to engineer novel multiferroics with phase‐change magnetoelectric responses, in addition to ferroelectrics with enhanced electromechanical performance. Here, the interplay among crystal structure, point defects, and multiferroic properties of the BiMnO₃–BiFeO₃–PbTiO₃ ternary system at its line of MPBs between polymorphs of tetragonal P4mm (polar) and orthorhombic Pnma (antipolar) symmetries is reported. A strong dependence of the phase coexistence on thermal history is found: phase percentage significantly changes whether the material is quenched or slowly cooled from high temperature. The origin of this phenomenon is investigated with temperature‐dependent structural and physical property characterizations. A major role of the complex defect chemistry, where a Bi/Pb‐deficiency allows Mn and Fe ions to have a mixed‐valence state, in the delicate balance between polymorphs is proposed, and its influence in the magnetic and electric ferroic orders is defined.     

Full in-situ characterization of spatial light modulators in an optical correlator. Filter adaptation to operating curves

Abstract

In this paper we present one method for the characterization of the spatial light modulators (SLMs) of a real-time Vander Lugt type of correlator. This correlator uses two SLMs: one to introduce the scene and a second to introduce the frequency‐matched filter. The SLM characterization methods are in situ, that is in the correlator set‐up. Illumination conditions are different for each SLM, and consequently different characterization techniques must be used in each case. For the characterization of the scene SLM a diffraction method is used, while for the characterization of the filter SLM an interferometric technique is more convenient. Finally, we take into account the operating curves of scene and filter SLMs in the design of the filter in order to optimize the correlation peak.     

Thermoeconomic analysis applied to an alternative wastewater treatment

This work develops a methodology for the determination of costs associated to products generated in a small wastewater treatment station. The methodology begins with plant units identification, relating their fluid and thermodynamics features to each point indicated in its process diagram. Following, a functional diagram and a formulation are developed in exergetic basis, describing all equations for these points, which are the constraints for optimisation and are used to determine costs associated to products generated in a Small Wastewater Treatment Station – SWTS. The methodology is applied to a hypothetical system based on SWTS plants and presents consistent results when compared to values based on previous experiments and evaluations.