Entanglement kinetics in polymer melts are chemically specific

Predictive modeling of the properties of polymeric material produced in next-generation manufacturing techniques requires knowledge of changes induced in the polymer microstructure during material processing. For instance, flow-induced disentanglement in fused-filament fabrication can decrease the strength of welds between printed layers. We have recently formulated a thermodynamically consistent constitutive equation that models entanglement kinetics to describe this behavior. The model predicts that the melt disentangles due to convective-constraint release and re-entangles on the Rouse time due to contour length fluctuations at the chain ends. A single fitting parameter β controls the rate of disentanglement; the remaining parameters in the model can be measured via model-independent experiments. We validate our model through comparison with molecular dynamics simulations. We determine β by fitting model predictions of disentanglement in steady-state shear to simulation measurements. Our model quantitively predicts re-entanglement following cessation of shear flow, confirming that the melt re-entangles on the Rouse time. We find that the rate of disentanglement is chemically dependent; stiffer melts disentangle faster more than more flexible melts.