(74d) Acute Sensitivity of Polymer Crystallization Phase Behavior to Intermolecular Interactions

Despite the prevalence of semicrystalline polymers in today’s markets, the fundamental mechanism of primary nucleation in polymer crystallization remains a subject of significant debate. Classical theories posit a one-step process, whereas more recent theories hypothesize a two-step process with a nematic intermediate. Molecular simulations of polymer crystallization have complicated the picture further; simulations give discordant results depending on the chosen models, processing conditions, and simulation techniques, and no consensus has emerged over the dominant nucleation mechanism. We hypothesize that a better understanding of the equilibrium phase behavior near the crystallization transition will be critical to reconciling simulations with one another and with theory. Accordingly, we construct temperature-volume phase diagrams for a variety of polymer models using advanced-sampling Monte Carlo techniques such as Wang-Landau and expanded ensemble density of states. For the present contribution, we will focus on the effects that model choices of the "polymer chemistry" (i.e. the pair-potential, bonding potential, angular potential, and torsional potential) have on the equilibrium phase diagram. We find that subtle model choices (e.g. discrete versus continuous, hard versus soft) have an order-one qualitative impact on the predicted nucleation mechanism. We will speculate on the consequences of this finding for the simulation literature and its implications on the search for a nucleation mechanism in polymer crystallization more broadly.

Funding Acknowledgement: We acknowledge support from the ACS PRF (59244-DN16), BYU’s Board of Trustees and BYU’s Office of Research Computing.