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Adsorption and Interfacial Properties of Fluids from Molecular Simulation

by Zhao, Xiongce

Abstract (Summary)
The objective of this research is to provide molecular-level insight on the adsorption and interfacial properties of fluids. Molecular simulation is the tool used to perform this work. The adsorption of polar and nonpolar molecules on carbonaceous adsorbents and metal surface is studied by using existing simulation techniques and new techniques developed by ourselves. The interfacial properties of quantum liquid mixtures are investigated using path integral simulations. The physical behavior of a DNA segment interacting with a novel adsorbent, single-walled carbon nanotubes (SWNTs), in aqueous environment is studied by molecular dynamics simulations. We have simulated the adsorption of propane on graphite surface. We obtain good agreement between simulations and experiments on both the isotherms and isosteric heat of adsorption. We have investigated five different propane potential models. We found that the fluid-fluid potential plays a significant role in determining the location of the 1-2 layering transition. We identified an orientational ordering transition for propane in the monolayer. In order to study the polar molecules adsorbed on graphite, we have developedpotential models including the graphite quadrupole and induction interaction between a polar molecule and the graphite surface. We have performed simulations of acetone adsorption on graphite to investigate the layering transitions, geometry, and coverage of acetone in the first, second and third layers. The simulation results agree well with the experimental observations. We have studied the structure of second layer physisorbed carbon monoxide on the Ag(110) metal surface. Both simulation and experiment found that the second layer CO molecules form orientationally ordered structures, with CO bond angles tilting at 45 degrees to the surface normal and azimuthal angles tilting in multiples of 45 degrees to the principal azimuth axis. From the simulation, we conclude that redistribution of charges within the first layer of CO on silver accommodate the formation of ordered second layer CO structures. We have performed parallel hybrid path integral Monte Carlo to study the interfacial properties of pure and mixture quantum liquids. We calculated the surface tension of pure liquid H2, pure liquid D2, and H2/D2 mixtures. The surface tension of pure fluids we calculated from simulations agree well with the experimental data. We observed interfacial segregation in the H2/D2 mixtures with H2 migrating to the surface. The H2/D2 mixture therefore exhibits negative deviations from ideal solution behavior. We studied the adsorption of a DNA segment with 12 base pairs on a (8,8) single walled carbon nanotube using the AMBER MD simulation software package. We found that the DNA adsorbs onto the wall of a regular SWNT or a positively charged SWNT, with a time scale of 100 pico-seconds. When the DNA is uncharged the end of the DNA molecule binds to the SWNT surface. DNA binds with its axis nearly parallel to a positively charged SWNT. The angle between the DNA and SWNT axes is about 20-30 degrees. In contrast, DNA does not bind to negatively charged SWNTs, because of the net negative charge on DNA. We found that the adsorption process does not affect greatly the structures of the DNA. However, the adsorption on a regular SWNT delays the A-form to B-form conversion for an A-DNA.
Bibliographical Information:

Advisor:Joseph J. McCarthy; J. Karl Johnson; Kenneth D. Jordan; Robert M. Enick

School:University of Pittsburgh

School Location:USA - Pennsylvania

Source Type:Master's Thesis

Keywords:chemical engineering

ISBN:

Date of Publication:03/11/2004

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