正十六烷体系凝固过程的分子动力学模拟

采用分子动力学模拟的方法,根据体系热容和自扩散系数的突变,计算了正十六烷体系以及正十六烷和降凝剂α-辛基萘、α-十二烷基萘及α-十六烷基萘等α-烷基萘混合体系的凝点,凝点降低结果与实验值相一致.用径向分布函数及末端距离分布对凝固温度附近体系的微观结构变化进行了研究.结果表明,凝固过程中正十六烷分子倾向于转变成为全反式的构象,以利于分子间平行有序的排列,这和熵减小的原理相一致.结合正十六烷的构象变化,探讨了烷基萘降凝的机理.

Molecular Dynamics Simulation on Solidification Process of n-hexadecane Systems

Molecular dynamics(MD) simulation was carried out to investigate the solidification processes of n-hexadecane system and the mixture of n-hexade cane with -alkyl naphthalene such as octyl,dodecyl and hexadecyl naphthalen e.The simulation box contained 10 n-hexadecane molecules and/or one -alky l naphthalene.Total 200 ps trajectory for each system was collected to execute t he structural,fluctuation and dynamic analysis.The calculated heat capacities of pure n-hexadecane system at 313 and 303 K were consistent with the experiment al ones.According to the sharp changes of heat capacities and self-diffusion c onstants with the simulation temperatures,the solidification point was identifie d for each system.It was found that the solidification point of n-hexadecane i s obviously lowered by mixing with -alkyl naphthalene,and the calculated so lidification points of four systems agreed with the experimental ones.The invest igation on the microstructures at temperatures before and after solidification r evealed that n-hexadecanes tend to arrange orderly during the solidifying proc ess,which is consistent with the fundamental of entropy-decrease.The reason wh y -alkyl naphthalene can lower the solidification point of n-hexadecane w as explained as due to the fact that the ring of -alkyl naphthalene was pa cked by several n-hexadecane molecules which made the order arrangement of n-hexadecane molecules more difficult.