Thesis (M.S. in Physics)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Young W. Kwon, James H. Luscombe. Includes bibliographical references (p. 29-31). Also available online.

Graphene is a single layer two-dimensional honeycomb lattice of carbon atoms. It is one of the toughest, lightest, and most conductive materials known. Graphene was first isolated using adhesive tape in 2004, and awarded the Physics Nobel Prize in 2010. Here we focus on the mechanical properties of graphene. First we present an analytical study, together with numerical simulations, of ripples in graphene. We show that ripples observed in free-standing graphene sheets can be a consequence of adsorbed OH molecules sitting on random sites. The adsorbates cause the bonds between carbon atoms to lengthen slightly. In the second part of this work we study the fracture mechanics of graphene. Experiments on free-standing graphene can expose the graphene sheets to out-of-plane forces. Here we show that out-of-plane forces can cause free-standing graphene to fracture. This fracture mode is known as the tearing mode and is common in materials such as paper. We present a numerical study of the propagation of cracks in clamped, free-standing graphene as a function of the out-of-plane force. We also obtain an analytical expression for the minimum force required to tear a two dimensional sheet, which is our model of graphene, in terms of the initial crack length. / text

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published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy

Hydrothermal fluids near and above the critical point of water have unique and potentially very useful thermophysical properties. At present, the lack of knowledge of supercritical water chemistry hinders implementation of innovative hydrothermal technologies. The development of new experimental methods and application of molecular modeling tools is clearly warranted to provide a better understanding of the complex properties of aqueous systems at elevated temperatures and pressures. The thermodynamic, dielectric and transport properties of hydrothermal fluids are investigated using Molecular Dynamics (MD) simulation and flow injection techniques. The spatial hydration structures and self-diffusion coefficients of phenol, aniline and naphthalene in aqueous infinitely dilute solution are examined from ambient to supercritical conditions by means of MD simulations. It is shown that the solvation shell around aromatic molecules undergoes significant changes along the liquid-vapour coexistence curve and, essentially, disappears at supercritical conditions. The changes in hydration structures are reflected in the values of the self-diffusion coefficients which dramatically increase near the critical point of water. The thermodynamic and dielectric properties of the Simple Point Charge Extended (SPC/E) water model are examined over a broad range of sub- and supercritical states. Accurate thermodynamic and dielectric equations of state (EOS) for the SPC/E water model are presented. The parameterizations provide the most accurate, up-to-date description of the properties of high-temperature SPC/E water, thus enabling for the direct comparison of molecular simulation results with experimental data via the corresponding states principle. The experimental methodology for the study of aqueous fluids at extreme conditions by using the ex situ flow injection technique is presented. The methodology significantly simplifies the technical aspects of flow injection analysis in hydrothermal fluids as sample injection and detection are performed at ambient temperature, thus allowing the use of standard on-line detection methods. The proposed ex situ experimental technique is applied to the examination of the hydrodynamic regime of a flow-through tubular reactor from ambient to supercritical water conditions. Application of the ex situ Taylor dispersion technique to measurements of the binary diffusion coefficients in hot compressed water is also presented. The ex situ flow injection methodology provides a basis for further development of flow injection analysis techniques at supercritical water conditions. / Thesis (Ph.D, Chemistry) -- Queen's University, 2009-03-05 17:39:30.197

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This thesis presents the ring polymer molecular dynamics (RPMD) approximation to the Kubo-transformed time correlation function and shows how it may be used as the basis of an approximate quantum-mechanical method for determining the dynamical properties of condensed-phase molecular systems. The performance of the RPMD method is initially investigated by calculating the position (q^ˆ), and position-cubed (q^ˆ3), autocorrelation functions of a series of onedimensional potential wells of varying anharmonicity. It is then applied to the evaluation of the incoherent dynamic structure factors of liquid para-hydrogen at 14 K. Finally, the RPMD method is used to determine canonical rate coefficients for two onedimensional models of bimolecular chemical reactions and a multidimensional model of a solution-phase proton transfer reaction. For each application, the accuracy of the RPMD method is established by comparison with exact quantum-mechanical results and/or with experiment. Throughout this work, an emphasis is placed upon identifying the situations in which the RPMD approximation breaks down. It is found that the RPMD method is capable of providing an accurate approximation to the time correlation functions of a variety of condensed-phase molecular systems. Situations for which it is inaccurate include correlation functions which correlate highly nonlinear operators and those involving significant quantum interference effects in the real-time dynamics.