Thermodynamic Investigation of thin n-Heptane films adsorbed on Magnesium Oxide (100) surfaces*

The thermodynamic properties of thin films of \textit{n-Heptane} on MgO (100) were measured using high resolution adsorption isotherms between 205 K and 275 K. Heats of adsorption were derived for first and second layer adsorbed on substrate and yield 42.38 $\pm $ 0.98 kJ/mol and 40.58 $\pm $ 0.46 kJ/mol, respectively. The isothermal compressibility was determined as a function of temperature and used to identify two possible phase transitions at 246.2 $\pm $ 1.5 K for the first and at 250.7 $\pm $ 0.8 K for the second layer respectively. These results will be compared to previous thermodynamic and neutron diffraction measurements of other shorter chained alkanes.