| Presented is a series of thermodynamic and neutron scattering experiments used to probe the nature of the hydrocarbon - MgO (100) interaction. High-resolution volumetric isotherms are used to probe the wetting, layer transitions, heats of adsorption, two-dimensional compressibilities, and identify possible phase transitions of thin films of benzene, ethane, and n-pentane on MgO powders. Neutron diffraction experiments were used to probe the structure and identify any phase transitions within monolayer films of ethane, butane and n-pentane.; Benzene adsorption, while showing no visible layering steps, shows a shift in the shape of the isotherm for p/po > 0:7. The change in isotherm behavior can be analyzed through use of the BET constant from fits to the experimental data. Ethane and n-pentane both show incomplete wetting with three and two distinct steps in their respective isotherms. Phase transitions from a two-dimensional liquid to a two-dimensional vapor were determined by examining the trend in the two-dimensional compressibilities for the first two layers of ethane (127 +/- 1K) and the second layer of pentane (183.8 +/- 4K). Neutron diffraction was used to study the structure of the ethane monolayer and determine that the structure of a monolayer of butane forms a commensurate 72x2R45° structure with p2gg symmetry and 4 molecules in the unit cell. By use of temperature dependent diffraction scans, the melting of the ethane (60K ≤ Tm ≤ 75K) and pentane (99K ≤ Tm ≤ 107K) were observed.; Combining the data sets from these two experimental techniques, preliminary two-dimensional phase diagrams can be proposed, the first step in characterizing the overall nature of the hydrocarbon-MgO interaction. |
