Molecular dynamics study on polymer filling into nano-cavity by injection molding

Abstract

Injection molding is one of the cost-effective technologies to produce polymer items towards mass production. In nano-injection molding, the final replication quality of nanostructures is strongly dependent on the filling quality in nano-cavities. In this paper, simulation models for polymer filling into nano-cavities were constructed to investigate the effects of molecular weight and cavity size. The glass transition temperature of isotactic PMMA with different molecular weights was calculated. Characteristics of configuration and snapshots during the filling process were analyzed. Density distribution, velocity profiles and mean-square gyration radius were proposed to investigate the filling quality and the flow behavior. Simulation results showed that the calculated glass transition temperature was higher than the experimental result and increased with the molecular weight. The filling behavior and final replication quality were highly depended on the molecular weight and the cavity size. A higher density distribution was observed in the edges along the nano-cavity by the nonbonding interactions. During the filling process, the gyration radius was firstly decreased rapidly, and then went up to approach the initial value. Atoms in central area exhibited the highest flow velocity, while the velocities of atoms were gradually decreased with the distance from the center.