Molecular dynamics simulation of bubble nucleation in Carbon Dioxide/Hexadecane Solution as an analog to foaming of polyethylene by Super Critical Carbon Dioxide

Abstract

A molecular dynamics model for microcellular foaming in carbon dioxide/hexadecane solution was introduced to investigate the super critical nucleation process in polyethylene. Hexadecane was chosen as a low molecular weight analog of polyethylene. The system was placed in a cube with periodic boundaries in all three dimensions, and run in NPT ensemble. A Nosé—Hoover thermostat was used to maintain the system temperature. A Berendsen barostat was utilized to carry out constant pressure ensemble simulations. An exp-6 field was employed to describe the force field. Methods to identify and trace nuclei were also proposed and the nucleation process was simulated. A series of snapshots were presented to visualize the early stage of bubble nucleation. Results showed that low-density gas nuclei were formed when the hexadecane and carbon dioxide saturated solution pressure was reduced. Then, carbon dioxide molecules would continue to enter into the gas phase until a bubble with a large number of gas molecules was formed.