We report high resolution electron microscope ͑HREM͒ observations and atomistic simulations of the bending of single and multi-walled carbon nanotubes under mechanical duress. Single and multiple kinks are observed at high bending angles. Their occurrence is quantitatively explained by

Synchrotron-based high-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of gold with titania and the chemistry of SO(2) on Au/TiO(2)(110) surfaces. The deposition of Au nanoparticles on TiO(2)(110) produces a system with an extraordinary ability to adsorb and dissociate SO(2). In this respect, Au/TiO(2) is much more chemically active than metallic gold or stoichiometric titania. On Au(111) and rough polycrystalline surfaces of gold, SO(2) bonds weakly and desorbs intact at temperatures below 200 K. For the adsorption of SO(2) on TiO(2)(110) at 300 K, SO(4) is the only product (SO(2) + O(oxide) --> SO(4,ads)). In contrast, Au/TiO(2)(110) surfaces (theta;(Au) < or = 0.5 ML) fully dissociate the SO(2) molecule under identical reaction conditions. Interactions with titania electronically perturb gold, making it more chemically active. Furthermore, our experimental and theoretical results show quite clearly that not only gold is perturbed when gold and titania interact. The adsorbed gold, on its part, enhances the reactivity of titania by facilitating the migration of O vacancies from the bulk to the surface of the oxide. In general, the complex coupling of these phenomena must be taken into consideration when trying to explain the unusual chemical and catalytic activity of Au/TiO(2). In many situations, the oxide support can be much more than a simple spectator.

Synchrotron-based high-resolution photoemission, X-ray absorption near-edge spectroscopy, and first-principles density functional (DF) slab calculations were used to study the interaction of NO(2) with a TiO(2)(110) single crystal and powders of titania. The main product of the adsorption of NO(2) on TiO(2)(110) is surface nitrate with a small amount of chemisorbed NO(2). A similar result is obtained after the reaction of NO(2) with polycrystalline powders of TiO(2) or other oxide powders. This trend, however, does not imply that the metal centers of the oxides are unreactive toward NO(2). An unexpected mechanism is seen for the formation of NO(3). Photoemission data and DF calculations indicate that the surface nitrate forms through the disproportionation of NO(2) on Ti sites (2NO(2,ads) --> NO(3,ads) + NO(gas)) rather than direct adsorption of NO(2) on O centers of titania. Complex interactions take place between NO(2) and O vacancies of TiO(2)(110). Electronic states associated with O vacancies play a predominant role in the bonding and surface chemistry of NO(2). The adsorbed NO(2), on its part, affects the thermochemical stability of O vacancies, facilitating their migration from the bulk to the surface of titania. The behavior of the NO(2)/titania system illustrates the importance of surface and subsurface defects when using an oxide for trapping or destroying NO(x)() species in the prevention of environmental pollution (DeNOx operations).

Dissipative particle dynamics (DPD) is a mesoscale modeling method for simulating equilibrium and dynamical properties of polymers in solution. The basic idea has been around for several decades in the form of bead-spring models. A few years ago, Groot and Warren established an important link between DPD and the Flory-Huggins chi-parameter theory for polymer solutions. We revisit the Groot-Warren theory and investigate the DPD interaction parameters as a function of bead size. In particular, we show a consistent scheme of computing the interfacial tension in a segregated binary mixture. Results for three systems chosen for illustration are in excellent agreement with experimental results. This opens the door for determining DPD interactions using interfacial tension as a fitting parameter.

Delivery of prebiotic compounds to early Earth from an impacting comet is thought to be an unlikely mechanism for the origins of life because of unfavourable chemical conditions on the planet and the high heat from impact. In contrast, we find that impact-induced shock compression of cometary ices followed by expansion to ambient conditions can produce complexes that resemble the amino acid glycine. Our ab initio molecular dynamics simulations show that shock waves drive the synthesis of transient C-N bonded oligomers at extreme pressures and temperatures. On post impact quenching to lower pressures, the oligomers break apart to form a metastable glycine-containing complex. We show that impact from cometary ice could possibly yield amino acids by a synthetic route independent of the pre-existing atmospheric conditions and materials on the planet.

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Energetic materials have been used for nearly two centuries in military affairs and to cut labor costs and expedite laborious processes in mining, tunneling, construction, demolition, and agriculture, making a tremendous contribution to the world economy. Yet there has been little advancement in the development of altogether new energetic motifs despite long-standing research efforts to develop superior materials. We report the discovery of new energetic compounds of exceptionally high energy content and novel polymeric structure which avoid the use of lead and mercury salts common in conventional primary explosives. Laboratory tests indicate the remarkable performance of these Ni- and Co-based energetic materials, while DFT calculations indicate that these are possibly the most powerful metal-based energetic materials known to date, with heats of detonation comparable with those of the most powerful organic-based high explosives currently in use.

Production of stable polymer-nanotube composites depends on good wetting interaction between polymer and nanotube, which is polymer specific, and depends in particular on chain conformation. In this paper, we examine this interaction for a conjugated, semiconducting polymer by a range of microscopic and spectroscopic techniques, to gain a greater understanding of the binding. Several interesting effects are observed, including an order to the interaction between the polymer and nanotube, the tendency of defects in the nanotube structure to nucleate crystal growth, and substantial changes in the spectroscopic behavior of the polymer due to the effect of the nanotubes on polymer conformation. This is substantiated by computational modeling, which demonstrates that these conformational modifications are due to the interaction with the nanotubes.