β-stretching parameter and Vogel–like temperature for reorientational relaxation from molecular dynamics of rod models with extended dipoles

Abstract

Molecular Dynamics simulations for systems of rods with a high extended dipole moment, consisting of charges of opposite sign located at the extremities of the rods, are shown. The rods interact through dispersion forces described by a Kihara intermolecular potential plus a coulombic term. Some features of undercooled liquids such as anomalous variation of transport coefficients with temperature at high and medium charges have been reported for these systems [J. Mol. Liq. 134, 136 (2007)]. In this work, results for the temperature dependence of translational and some orientation autocorrelation functions for the mentioned models are presented and discussed. The rods show a typical Kohlrausch time decay for high dipoles and a typical Einstein decay for low and null dipoles with intermediate behaviour in between. For the reorientation relaxation, the stretching β parameter and Vogel-like temperatures are calculated showing a slight dependence on the order of the reorientational autocorrelation function but a deeper dependence on charge distribution.

Keywords:

• Molecular Dynamic
• extended dipoles
• reorientational relaxation
• undercooled liquids

Acknowledgements

This work was funded by grants CTQ2007-60910 of the Spanish Ministry for Education and Science (MEC) and P07-FQM-02496 of the Regional Government of Andalusia.