从常温常压到超临界乙醇的分子动力学模拟

Molecular dynamic simulation of ethanol from ambient temperature and pressure to supercritical conditions

采用分子动力学方法系统地研究了从常温常压到超临界状态乙醇的热力学性质、结构性质和动力学性质.模拟发现随着温度的升高,体系焓值增大,乙醇分子间的氢键作用减弱,自扩散系数增大;随着压强的增大,乙醇分子间的氢键作用增强,自扩散系数减小;乙醇自扩散系数在液相区随温度变化不明显,在气相区随压强增大很快减小,超临界区乙醇的自扩散系数比液相区大十几倍.温度和压强对乙醇自扩散系数的影响可通过密度来体现.与常温常压相比,超临界条件下的乙醇体系因密度涨落存在分子聚集现象,且在低密度区域更显著;乙醇分子间的氢键作用明显减弱,结构变得松散,分子极性降低.本文结果与已有实验值符合得较好.

The thermodynamic properties,structure,and dynamic properties of ethanol from ambient conditions to supercritical states were investigated by molecular dynamics simulation（MD）.With the increase of temperature,the enthalpy and self-diffusion coefficients increase,while the hydrogen bonding interaction between ethanol molecules weakens.With the increase of pressure,the self-diffusion coefficients decrease,while the hydrogen bonding interaction increases.The self-diffusion coefficient of ethanol in supercritical region is 10 times greater than that in the liquid region.It changes slightly with temperature in the liquid region,while decreases rapidly with pressure in the gas region.The influence of density on self-diffusion coefficient could be manifested by the influence of temperature and pressure.Under supercritical conditions,the ethanol system shows aggregation phenomenon which is even more evident in the low-density region due to density fluctuations.The hydrogen bond of ethanol molecules significantly weakens,the structure becomes loose and the molecular polarity is greatly reduced in supercritical conditions compared with that in ambient conditions.Our results are in good agreement with the experimental data.