The physical adsorption of a fluid by a solid is a subject of broad scientific and engineering interest. In this dissertation we explore some of the molecular aspects of this phenomenon through the use of computer simulations. We have developed a Monte Carlo simulation technique in the isobaric-isothermal ensemble for studying adsorption equilibria at a planar fluid-solid interface. This technique has characteristics which make it particularly useful for studies of adsorption involving fluid mixtures and for thermodynamic states near phase boundaries. Simulation at constant pressure has a number of advantages. Principal among these is that it closely parallels the manner in which adsorption is often studied experimentally. We have applied the isobaric Monte Carlo method in three studies of the molecular physics of adsorption. The first investigates the relationship between adsorption of a vapor in the approach to saturation and wetting phenomena. We have found conclusive evidence for a transition between partial and complete wetting of the interface in the fluid argon-solid carbon dioxide model system. This transition is accompanied by first-order surface phase transitions between thin and thick adsorbed films, called prewetting transitions. The observation of these transitions verify important predictions of modern theories of interfacial thermodynamics, especially density functional theory. The second and third studies examine the molecular basis for adsorption separations of vapor and liquid mixtures. Simulation results for loading and selectivity obtained for binary vapor mixtures are compared with predictions of two dimensional adsorbate and ideal adsorbed solution theories for vapor mixture adsorption. Through these comparisons we demonstrate how simulations can be used to assess the consequences of theoretical assumptions and approximations. We also demonstrate the feasibility of using simulations to study the molecular aspects of liquid mixture adsorption. Surface excess isotherms and density profiles for two model systems are obtained via simulation.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7806 |
| Date | 01 January 1990 |
| Creators | Finn, John Edward |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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