Gas-liquid critical behavior of dipolar soft spheres
Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Final Report Abstract
The existence of gas–liquid coexistence in dipolar fluids with no other contribution to attractive interaction than dipole-dipole interaction is a basic and open question in the theory of fluids. We succeeded in computing the gas-liquid critical point in a system of dipolar soft spheres subject to an external electric field using molecular dynamics computer simulation. Tracking the critical point as the field strength is approaching zero we find the following limiting values: Tc = 0.063 and ρc = 0.0033 (dipole moment µ = 1). These values are confirmed by independent simulation at zero field strength. In addition the gas-liquid critical parameters of charged soft dumbbells (CSDs) as function of the site-to-site separation on the dumbbells, d, were obtained on the basis of molecular dynamics computer simulation. A mean field theoretical description was developed, explaining the results at small and large dumbbell lengths, d. In the limit d → 0 the CSD system exhibits gas-liquid phase separation solely driven by repulsion and dipoledipole interaction. If the dumbbell bond is eliminated the CSD system becomes similar to the restricted primitive model of ionic fluids with hard core repulsion replaced by soft repulsion. The gas-liquid critical parameters were obtained for this model and discussed in relation to the CSD system. We believe that this work significantly adds to the understanding of phase transition behavior in polar liquids.
Publications
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Gas-liquid coexistence in a system of dipolar soft spheres, Physical Review E 82, 062501 (2010)
Ran Jia, Heiko Braun
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Phase coexistence for charged soft dumbbell and ionic soft sphere systems via molecular dynamics simulation, Physical Review E 87, 012311 (2013)
Heiko Braun, Reinhard Hentschke
