Enhanced nucleation of bimodal molecular weight distribution polymers: A molecular dynamics study

Abstract

Abstract We perform coarse-grained molecular dynamics (CGMD) simulations to study the homogeneous nucleation of bimodal and unimodal molecular weight distribution polymers with equivalent average molecular weight. First, a statistical method is proposed to determine the critical nuclei and thus calculate the free energy barrier of nucleation. From the temperature dependence of diffusion coefficient, we also determine the activation energy of diffusion. Then we calculate the nucleation rate and find that it is consistent with the classical nucleation theory for homogeneous nucleation in semi-crystalline polymers. Compared with unimodal system, the bimodal system exhibits lower interfacial free energy and consequently lower free energy barrier for nucleation, while the two systems have similar activation energy for diffusion. This suggests that the promoted nucleation rate of bimodal molecular weight distribution polymer is a result of the reduction of interfacial free energy, which is eventually a consequence of chain-folding nucleation of long chain component.