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

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.