Molecular dynamics study on interface properties and interphase transport

Liquid-vapor interface characteristics and interphase transport, including interface thickness, thermodynamic parameters, configuration and related evaporation and condensation phenomena, are investigated by molecular dynamics simulations. Combining this work with existing theoretical and computational study, the understanding on interface behaviors and evaporation and condensation phenomena is updated. In the simulation on thermodynamics parameters of liquid-vapor interfaces in equilibrium, it is found that there exists a non-equilibrium molecular kinetic energy distribution through the interface, which confirms that though a liquid-vapor interface is in thermostatic equilibrium, it may be not in thermokinetic equilibrium. Furthermore, although the density varies in a continuous manner from the liquid to the vapor, the density fluctuation in the transition region is larger than the values in the bulk phases. MD simulations show that liquid-vapor interface is a wavy surface varying with time. The wavy interface configuration plays an important role on the molecular evaporation and condensation processes, which make evaporation and condensation processes correlated. In this presentation, the kinetics of evaporation and condensation is studied. Base on these MD simulations, the foundation of the classical evaporation and condensation theory is investigated. Among the simplifications of the classical evaporation and condensation theory, the assumptions of no molecular reflection, independence between evaporation and condensation, and no temperature jump may result in considerable discrepancies between the theoretical prediction and the real evaporation/condensation flux.