Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 3: Liquid Crystals and Polar Fluids

CPP 3.5: Talk

Monday, February 25, 2008, 11:15–11:30, C 264

Gas-Liquid Phase Behavior of Dipolar Fluids — •Jörg Bartke and Reinhard Hentschke — Bergische Universität Wuppertal, Germany

The gas-isotropic liquid-nematic liquid phase behavior of the Stockmayer fluid is studied using Molecular Dynamics simulation over a wide range of dipole strengths. In our simulations we do not observe the disappearance of the isotropic gas-isotropic liquid coexistence at high dipole strength contrary to earlier findings based on Monte Carlo techniques. Even though the formation of reversible dipole chains strongly affects the location of the critical point, it does not lead to its disappearance. In addition to the simulation results we present a theory explaining the dependence of the gas-liquid critical point in the Stockmayer fluid on the dipole strength. The theory is based on the Flory-Huggins lattice description for polymer systems in conjunction with a transfer matrix model for isolated chains of reversibly assembled dipolar particles. We find that the shift of the critical point as function of dipole strength, also observed in computer simulation, strongly resembles the critical point shift as function of chain length in ordinary linear polymer systems. In particular the decrease of the critical density with increasing dipole strength is a consequence of the existence of reversible chains near criticality.