A Molecular Dynamics Study of Interface Phenomena of a Liquid Droplet

Liquid droplets of argon surrounded by the vapor for various temperatures and various sizes have been simulated by the molecular dynamics method. Macroscopic characteristics of droplets such as density and pressure profiles and surface tension are estimated. The largest droplets with the equimolar dividing radius of about 20 Å resemble to the saturated macroscopic drops. Smaller droplets have slightly smaller surface tension. To explore the surface phenomena of droplets in more detail, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. By observing the instantaneous kinetic and potential energies of each molecule, the time scale of the 'phase change' of each molecule is estimated. The number flux of molecules across the liquid-vapor interface is counted. It is demonstrated that the rate of 'phase change' events of molecules is proportional to the vapor pressure.