Role of flow-induced nematic order in polyethylene nucleation*

We employ united-atom molecular dynamics (MD) simulations to quantify the role of nematic order in polyethylene (PE) nucleation. In our simulations, stretched periodic PE chains are blended with free PE chains of the length of 500 and 1000 backbone carbons (C500 and C1000). These bidisperse systems are the simplest realizations of real polymer samples, in which only polymers with long branches or high molecular weights are stretched by flows. By simulating isothermal nucleation and performing mean-first-passage time analysis for the growth of the largest nucleus in our simulations, we show that the nucleation rate of PE increases exponentially with increasing average nematic order of monomers. We also validate the predicted quiescent nucleation rates by computing the crystallization half-time at various temperatures using the crystal growth velocity, sampled from simulations of isothermal crystallization of chains near crystalline slabs, and the Avrami equation. The predicted crystallization half-times agree with experiments, suggesting our predicted nucleation rates are reasonable.