Understanding Polymer Crystallization through Large Scale Coarse-grained Molecular Dynamics Simulations

Semi-crystalline polymers play important roles in many engineering applications. The morphological and mechanical properties of semi-crystalline polymers are strongly influenced by their microstructures. Nevertheless, there is limited understanding on the crystallization and microstructures of semi-crystalline polymers. Here we have developed temperature-transferable and efficient coarser-grained molecular dynamics models for two representative polymers, polyethylene (PE) and polydimethylsiloxane (PDMS). We perform extensive coarser-grained molecular dynamics simulations with more than 1 million atoms to study crystallization of entangled PE and PDMS melts under quenching process. With the help of entanglement network analysis, the crystalline stem length obtained by quenching the melts below melting temperature displays a linear relation with the entanglement length in the homogeneous polymer melt above the crystallization temperature. Chain folding numbers are found to be very close to those in pure melts at different initial temperatures, and they tend to moderately decrease with increasing concentration of the long polymers. The simulation results suggest that the topological restriction of entanglements is a universal property to control the thickness selection during polymer crystallization.