Multilayered nature in crystallization of polymer droplets studied by MD simulations: Orientation and entanglement

The chain orientation, local entanglement and crystallization behavior of polymer droplets are studied by Molecular Dynamics (MD) simulations. In addition to the traditional concepts of bulk and surface for a liquid droplet, there is a unique region for polymer droplets, in which the surface effect transfers into the interior of droplets via polymer chains. The range of this intermediate region is strongly related to chain size. During a continuous cooling, the nucleus preferentially appear in this intermediate region and are aggregated subsequently, which are attributed to a pre-orientation near the surface and a lower local entanglement (for long chains). The chain orientation varies from perpendicular-to-surface for short chains to parallel-to-surface for long chains. Our results reveal the multilayered nature of polymer droplets and shed a light on the comprehensive understanding of polymer crystallization near a spherical free surface.