On the Phase Equilibrium of Polar Fluids Using the Dipolar Yukawa Fluid Molecular Model

The fluid phase equilibrium of polar fluids is investigated using the dipolar Yukawa fluid (DY) molecular model. The dispersion forces and the electrostatic interactions are represented by the hard core Yukawa fluid molecular model and the dipole-dipole interaction, respectively. It is shown that the liquid-vapor (L-V) coexistence phase equilibrium, similar to that for the Stockmayer fluid model (STM), that uses the Lennard-Jones (LJ) potential model plus the dipole-dipole interaction can be obtained using the DY molecular model. Results show that for the special case of the parameter value of the Yukawa potential, z = 1.8/sigma, the thermodynamic functions of the Yukawa fluid are very similar to those of the LJ 12:6 fluid, and the STM potential model can be replaced by the more easily employed DY. Results for the L-V coexistence phase equilibrium of polar liquids are presented for polar fluids with dipolar strength of mu(2)/epsilon sigma(3) = 1, 2, 3, and 4 and show good agreement with GENIC computer simulations of the STM fluid. It is also shown that as the dipolar strength of the polar fluid increases, similarly to accurate calculations using the STM, the L-V phase equilibrium coexistence curves do not present any undesirable unusual behavior that has been seen in some approximate calculations.