Diffusion Behavior of n-Alkanes by Molecular Dynamics Simulations

Bulletin of the Korean chemical society

Song Hi Lee¹  Taihyun Chang¹  Gihong Sung¹  Geun Hoi Goo¹ 

关键词: Molecular dynamics simulation;    Diffusion coefficient;    n-Alkanes;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

In this paper we have presented the results of diffusion behavior of model systems for eight liquid n-alkanes (C₁₂-C₄₄) in a canonical (NVT) ensemble at several temperatures using molecular dynamics simulations. For these n-alkanes of small chain length n, the chains are clearly ee²>/6g²>>1 and non-Gaussian. This result implies that the liquid n-alkanes over the whole temperatures considered are far away from the Rouse regime, though the ratio becomes close to the unity as n increases. Calculated self-diffusion constants D_self are comparable with experimental results and the Arrhenius plot of self-diffusion constants versus inverse temperature shows a different temperature dependence of diffusion on the chain length. The global rotational motion of n-alkanes is examined by characterizing the orientation relaxation of the end-to-end vector and it is found that the ratio �?₁/�?₂ is less than 3, the value expected for a isotropically diffusive rotational process. The friction constants ヮof the whole molecules of n-alkanes are calculated directly from the force auto-correlation (FAC) functions and compared with the monomeric friction constants �?_D extracted from D_self. Both the friction constants give a correct qualitative trends: decrease with increasing temperature and increase with increasing chain length. The friction constant calculated from the FAC’s decreases very slowly with increasing temperature, while the monomeric friction constant varies rapidly with temperature. By considering the orientation relaxation of local vectors and diffusion of each site, it is found that rotational and translational diffusions of the ends are faster than those of the center.

【 授权许可】

Unknown