Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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Centre for Nanotechnology Research

Nonequilibrium molecular dynamics calculations have been carried out o Lennard-Jones binary mixtures with the aim to investigate the dependence of the Soret coefficient on the temperature and on the composition for systems presenting phase transitions. By an appropriate choice of the cross interaction parameter, ε12 (0&lt; ε12 &lt;min { ε11, ε22 }), these systems show a mixing/demixing (consolute) phase transition. The other parameters are those of a binary mixture of Argon and Krypton. This system has been considered over a wide range of temperatures (up to ≃1000 K), of compositions (0.1≤ x1 ≤0.9), and of cross interaction parameter (0&lt; ε12 &lt;min { ε11, ε22 }). The study allows the formulation of a very simple expression for the Soret coefficient, S T, as a function of temperature and composition. Indeed the computed values of ST in the one phase region outside the critical region are closely fitted by the function [T- Tc (x1)] -1 where Tc (x1) is the demixing temperature of the mixture under study. This result indicates for this type of systems a dependence of S T, as a function of the temperature, on a unique characteristic property of the fluid mixture, the demixing temperature Tc, which, in turn, is a function of the binary mixture composition x1. © 2010 American Institute of Physics.

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Journal of Chemical Physics

Temperature and composition dependence of the Soret coefficient in Lennard-Jones mixtures presenting consolute critical phenomena

Au(0)/POSS (Octa(aminophenyl) Silsesquioxane) composite was synthesized by chemical reduction of auric acid using glycerol as reducing agent. The morphology and physicochemical properties of Au/POSS nanocomposite were characterized by NMR, FT-IR and TEM spectroscopy. The Au/POSS nanocomposite electrode was used for the oxidation of glucose. The results indicate that the Au/POSS nanocomposite film was highly sensitive and suitable for glucose in 0.5 M NaOH. The presence of ascorbic acid in analyte gave no error in detection of glucose for measuring 5 mM glucose, which is the normal physiological level in blood. Further, Au/POSS nanocomposite showed an enhanced antibacterial activity even higher than standard ciprofloxacin. Hence, Au/POSS nanocomposite acts as a strong antibiocides as well as selective electrodes towards glucose oxidations. Copyright © 2009 American Scientific Publishers.

Journal of Nanoscience and Nanotechnology

Synthesis and Characterization of Au/POSS Composite Powder for Bio-Fuel Cells and Antibiotic Applications

A potent catalyst has been prepared consisting of platinum (Pt), and platinum-palladium (Pt-Pd) nanoparticles supported on purified single-walled carbon nanotubes (Pt/CNT and Pt-Pd/CNT). Electrochemical characteristics of formic acid and formaldehyde oxidation on these catalysts are investigated via cyclic voltammetric analysis in mixed 0.5 M HCOOH (or 0.5 M HCHO) and 0.5 M H2SO4 solutions. The results imply that the Pt-Pd/CNT electrodes exhibit a better activity than the corresponding Pt nanoparticles modified SWCNT electrodes. The modified electrode exhibits significant electrocatalytic activity towards formic acid and formaldehyde oxidation, which may be attributed due to the uniform dispersion of nanoparticles on SWCNTs and the efficacy of Pd species in Pt-Pd system. Such nanoparticles modified CNT electrodes exhibit better catalytic behavior towards formic acid and formaldehyde than the corresponding carbon electrodes, indicating that the system studied in the present work is the more promising system for use in fuel cells. © 2009.

Journal of Colloid and Interface Science

Electrocatalytic oxidation of formic acid and formaldehyde on nanoparticle decorated single walled carbon nanotubes

Proton conductivity of membranes depends on different scale phenomena: from the hopping of single protons between neighboring water molecules to the macroscopic structure of the porous membrane. While the most accurate approach to model the proton hopping is quantum mechanics, the modeling of macroscopic membrane properties as conductivity or permeability requires a higher-level description. Therefore, in order to contribute to the design of novel membranes, a successful modeling approach should be able to describe macroscopic properties, without losing the information about the basic mechanisms of proton transport. In this article, after an extensive list of modeling approaches outlining advantages and disadvantages of each of them, two possible strategies for including proton hopping description in higher-scale modeling are described in detail. The first strategy consists of supplying a classical molecular dynamics with a reactive force field (RFF), which, allowing for breaking and formation of oxygen-hydrogen bonds, is able to describe the proton hopping mechanism and structural and dynamical properties of membranes. The second approach consists of a phenomenological description of the membrane conductivity, which, by describing the hydrated membranes as acid solutions inside porous media, allow to infer the effects of basic proton transport mechanisms from experimental data on bulk acid solutions. © 2009 Elsevier B.V. All rights reserved.

Encyclopedia of Electrochemical Power Sources

Fuel Cells - Proton-Exchange Membrane Fuel Cells | Membranes: Modeling

In the present publication an automated computational method for cluster analysis of crystal structures (and/or their powder diagrams) is described. The clustering bases on the similarity index obtained by comparing of powder diagrams. This approach allows a quick detecting of manifold crystal structures in extensive data sets, an estimation of the number of minima for an energy landscape, a control over the progress of crystal structure generation during runtime, and a quick analysis of results of crystal structure predictions. © 2009 Elsevier B.V. All rights reserved.

Chemical Physics Letters

Cluster analysis and completeness of crystal structure generation

The structure and interactions of water species in hydrated Nafion membranes as a function of water content were investigated on the basis of medium-infrared spectral analysis and molecular dynamics (MD) simulations. The spectral decomposition of the FT-IR data in the stretching OH region was performed on different levels of hydration of the sulfate functional groups (λh2o/rso3- = 2-22). Quantum mechanical calculations of two model systems [perfluoroethanesulfonic acid/(H 2O)6 cluster] and a [perfluorobutanesulfonic acid/(H 2O)6 crystal] were carried out in order to account for the band assignments of Nafion in the stretching OH region (2500-4000 cm -1). Our findings indicated that the secondary structure of water species in Nafion can be accurately explained in terms of our reactive force field for water. The distinction between "surface" and "bulk" water contributions in Nafion membrane pores is proposed along with a quantitative estimate of the different types of OH groups present in the system. The average pore size was calculated and supported by the spectral results. © 2009 American Chemical Society.

Journal of Physical Chemistry B

Investigation of water structure in Nafion membranes by infrared spectroscopy and molecular dynamics simulation

In this work, we present a new approach to model the conductivity of polymeric sulfonated membranes. In the first part, we develop a model for the proton conductivity in a bulk acid solution. The model describes the vehicular and structural diffusion mechanisms at different proton concentrations as a function of four parameters with well defined physical meanings. These parameters are adjusted by fitting the experimental proton conductivity in a hydrochloric acid solution. In the second part, the effects of the presence of the porous membrane on the proton conductivity are added to the model. As a result, the model predicts the membrane conductivity as a function of its hydration level and porous structure. In the absence of experimental data on the membrane porous structure, the model can be used to predict the membrane porous structure once membrane conductivities are experimentally known. In this scope, in the third part, we provide a simple analytical description of the porous membrane based on the percolation theory depending on two structure parameters. A side result of the conductivity model is to provide analytical expressions for the drag coefficient, pore diameters and water permeability. All obtained results compare very well with experimental data. © 2008 Elsevier B.V. All rights reserved.

Solid State Ionics

An analytical model for the conductivity of polymeric sulfonated membranes

In this paper the thermodiffusive behavior of an equimolar binary mixture subject to repulsive potentials of the form (/r) n is investigated by using nonequilibrium molecular dynamics (NEMD) and the thermodiffusion (Soret) coefficient, ST, is computed in a wide range of temperatures. With the aim to contribute to the study of the dependence of the Soret coefficient on the interaction potential, the exponent n of the potential is varied from 1 to 12, that is from a pseudocoulombian to a pseudohard-sphere interaction. The steady state equation is integrated for the composition function under reasonable assumptions and it is shown that in some cases the request for it to be linear cannot be satisfied. For this reason nonlinear functions are used to fit the NEMD composition data. The simulations indicate a negligible dependence of ST on the composition (in the composition range here considered) while the dependence on the temperature is more marked. The computed values of ST as a function of the temperature are fitted with analytical functions. It is found that with n3 (medium and short range interaction) the model system behaves like a dilute gas mixture with the Soret coefficient varying with the temperature almost like 1/T. In the case of n=1 (long range interaction), ST has a more complex dependence on T: in particular it shows a change of sign. The analytical fitting functions, ST (T), are used in the integrated steady state equation thus obtaining the steady state composition profile and its comparison with the NEMD results indicates the grounding of the approach here proposed. © 2008 American Institute of Physics.

Influence of the interaction potential and of the temperature on the thermodiffusion (Soret) coefficient in a model system

We apply a newly parameterized central force field to highlight the problem of proton transport in fuel cell membranes and show that central force fields are potential candidates to describe chemical reactions on a classical level. After a short sketch of the parameterization of the force field, we validate the obtained force field for several properties of water. The experimental and simulated radial distribution functions are reproduced very accurately as a consequence of the applied parameterization procedure. Further properties, geometry, coordination, diffusion coefficient and density, are simulated adequately for our purposes. Afterwards we use the new force field for the molecular dynamics simulation of a swollen polyelectrolyte membrane similar to the widespread Nafion 117. We investigate the equilibrated structures, proton transfer, lifetimes of hydronium ions, the diffusion coefficients, and the conductivity in dependence of water content. In a short movie we demonstrate the ability of the obtained force field to describe the bond breaking/formation, and conclude that this force field can be considered as a kind of a reactive force field. The investigations of the lifetimes of hydronium ions give us the information about the kinetics of the proton transfer in a membrane with low water content. We found the evidence for the second order reaction. Finally, we demonstrate that the model is simple enough to handle the large systems sufficient to calculate the conductivity from molecular dynamics simulations. The detailed analysis of the conductivity reveals the importance of the collective moving of hydronium ions in membrane, which might give an interesting encouragement for further development of membranes. Figure: The structure of water in one pore of the highly hydrated Nafion membranes. © Springer-Verlag 2007.

Journal of Molecular Modeling

Molecular dynamics simulation of hydrated Nafion with a reactive force field for water

Uniform and stable polymer protected spherical platinum, palladium, silver and ruthenium nanoparticles were synthesized using glycerol both as solvent as well as reducing agent. A comparative study was done on the mode of heating viz reflux and microwave (MW) on the size and morphology of nanoparticles. Further it was observed that the morphology of the particles varied from spherical to triangular prism in the case of palladium nanoparticles when the reaction was changed from normal mode of reflux condition to microwave mode (MW) of heating. Triangular prismatic and spherical metal nanoparticles were characterized using UV-vis spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. © 2007 Elsevier B.V. All rights reserved.

Materials Chemistry and Physics

One pot synthesis of polymer protected Pt, Pd, Ag and Ru nanoparticles and nanoprisms under reflux and microwave mode of heating in glycerol—A comparative study