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The motion of a tiny air bubble in an aqueous solution of cetyl trimethyl ammonium bromide and sodium salicylate (CTAB/NaSal), which forms wormlike micelles, was observed using a high-speed polarization camera. Complex local flow is observed around the bubble surface because the bubble shape deforms repeatedly at 100 Hz. The camera can be used to measure the retardation distribution, which is related to the stress field around the bubble. Different retardation and orientation angle distributions were observed during the contraction and expansion phases. In the contraction phase, a strong retardation distribution appears at the tail of the cusped bubble. The occurrence of uniaxial elongation deformation is considered to be due to the negative wake because they are closely correlated. In contrast, a weak retardation distribution spreads at the upper side of the bubble during the expansion phase, where biaxial extensional deformation occurs due to expansion of the bubble surface. These significant changes in strong elastic stress distributions, which correspond to the orientation angle profiles, can result in increase of bubble rising velocities.

WOS: 000288825800039, The percolating paths of the carbons and electrolytes in a cathode catalyst layer (CCL) could be successfully visualized in three-dimensions in order to investigate both the electronic and ionic connectivity by modeling a three-dimensional (3-D), meso-scale CCL of a polymer electrolyte membrane fuel cell (PEMFC). The effective Knudsen diffusion coefficients could also be obtained by computing pore tortuosity values. Electrochemical simulation studies were carried out by feeding air at 70 degrees C. Low platinum (Pt) loading (0.1 mg cm(-2)) catalysts with ionomer contents ranging from 14 to 50% were studied. The performance of a PEMFC electrode was affected by the ionomer content which is optimal at about 33%. In this case, both electronic and ionic connectivity produced the broadest active surface area of the Pt catalyst. The polarization drop tendency was in good agreement with the experiment, and this percolation study could successfully explain the existence of an optimum amount of ionomer. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

We propose a statistical-mechanical methodology to estimate ‘slow’ diffusivity from conventional molecular dynamics (MD) calculations. In this method, the temperature dependence of the Helmholtz free energy profiles is predicted from one MD simulation at a particular temperature. These profiles are used to estimate the diffusivity, combined with transition state theory. We apply this methodology to molecular diffusion in a zeolite nanopore. Our methodology promises the efficient estimation of molecular ‘slow’ diffusivity in nanopores, e.g., values less than 10 −14 m 2 /s.

A methodology based on a molecular simulation technique and permeation theory was applied to the systematic estimation of permeabilities of inorganic gases (Ar, He, Ne, N 2 , O 2 ) through an MFI-type silicalite membrane. The estimated inorganic gas permeabilities were in qualitative agreement with available experimental data. The estimated permeabilities decrease in the order N 2 >O 2 >Ar>Ne>He. This result means that their permeation mechanism is significantly influenced by their adsorption properties rather than by their kinetic properties, and can be described by the adsorption model. The qualitative agreement of the calculated permeability with experiment suggests that the method used is a leading candidate for the theoretical approach to the prediction of the performance of zeolite membranes.

The notion of “active sites” is fundamental to heterogeneous catalysis. However, the exact nature of the active sites, and hence the mechanism by which they act, are still largely a matter of speculation. In this study, we have presented a systematic quantum chemical molecular dynamics (QCMD) calculations for the interaction of hydrogen on different step and terrace sites of the Pd (3 3 2) surface. Finally the dissociative adsorption of hydrogen on step and terrace as well as the influence of surface hydrogen vacancy for the dissociative adsorption of hydrogen has been investigated through QCMD. This is a state-of-the-art method for calculating the interaction of atoms and molecules with metal surfaces. It is found that fully hydrogen covered (saturated) step sites can dissociate hydrogen moderately and that a monovacancy surface is suitable for significant dissociative adsorption of hydrogen. However in terrace site of the surface we have found that dissociation of hydrogen takes place only on Pd sites where the metal atom is not bound to any pre-adsorbed hydrogen atoms. Furthermore, from the molecular dynamics and electronic structure calculations, we identify a number of consequences for the interpretation and modeling of diffusion experiments demonstrating the coverage and directional dependence of atomic hydrogen diffusion on stepped palladium surface.

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