Molecular Dynamics of Nucleation and Crystallization of Polymers

Abstract

Nucleation and crystallization of isotactic polypropylene (iPP) has been simulated using molecular dynamics (MD) with and without nucleating agents. MD simulations were carried out with four iPP chains of 90, 180, 270, and 360 backbone carbons each in the presence of a number of derivatives of dibenzylidene sorbitol (DBS) as nucleators. A novel method was developed to analyze the results of molecular dynamics and to elucidate the molecular phenomenon of nucleation in the early stages of crystallization. This new method retrieves and compares the backbone conformation of iPP in the liquid state to that available in the crystalline form and enumerates the number of crystallizing sites (or nuclei) formed during the simulation. The comparison of the number of nuclei formed, during the simulation of iPP crystallization with and without nucleators, allows the comparison of the effectiveness of nucleators and therefore can be used as a screening tool to screen a large number of potential nucleators. Simulation results are compared to literature data and indicate the method can distinguish nucleator effectiveness.