Viscosity and Diffusion Constants Calculation of n-Alkanes by Molecular Dynamics Simulations
Bulletin of the Korean Chemical Society (Print)
In this paper we have presented the results for viscosity and self-diffusion constants of model systems for four liquid n-alkanes (C 12 , C 20 , C 32 , and C 44 ) in a canonical ensemble at several temperatures using molecular dynamics (MD) simulations. The small chains of these n-alkanes are clearly /6>1, which leads to the conclusion that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime. Calculated viscosity η and self-diffusion constants D are
... constants D are comparable with experimental results and the temperature dependence of both η and D is suitably described by the Arrhenius plot. The behavior of both activation energies, E η and E D , with increasing chain length indicates that the activation energies approach asymptotic values as n increases to the higher value, which is experimentally observed. Two calculated monomeric friction constants ζ and ζ D give a correct qualitative trend: decrease with increasing temperature and increase with increasing chain length n. Comparison of the time auto-correlation functions of the end-toend vector calculated from the Rouse model for n-dodecane (C 12 ) at 273 K and for n-tetratetracontane (C 44 ) at 473 K with those extracted directly from our MD simulations confirms that the short chain n-alkanes considered in this study are far away from the Rouse regime.