Molecular Shape, Polarity and Departures from the Principle of Corresponding States

摘要

The objective of the report is to describe theoretical research into vapor-liquid equilibria of fluids with nonspherical molecular shape and dipole-dipole interactions. The work described is used to investigate how the sources of anisotropy influence departures from the principle of corresponding states. A theory which predicts the contributions to the structure and thermodynamics of fluids arising from multipolar interactions or other long ranged forces in the presence of nonspherical molecular shape is developed. Fluid phase diagrams have been determined for single component diatomic fluids modeled with site-site Lennard-Jones 12-6 potentials. The results have been used to show how molecular shape effects determine departures from corresponding states. The theory correctly predicts the trends in critical density and temperature with increasing anisotropy seen in nonpolar molecules. Also studied were the phase diagrams of diatomic molecules with dipole-dipole interactions. Increasing the dipole moment in common with increased nonspherical molecular shape increases departures from corresponding states. However, polarity and nonspherical molecular shape are coupled in a nontrivial manner and their effects on the phase diagram are not additive.