Phase behavior and alignment transition of ultra high molecular weight polyethylene/polyamide 6 blends under extensional and shear flow

Herein, we have, for the first time, presented detailed comparative studies on complex phase behavior and alignment transition of ultra high molecular weight polyethylene/polyamide 6 (UHMWPE/PA6) blends under unconventional extensional flow and traditional shear flow by combined atomistic and mesoscopic simulation. The Flory-huggins interaction parameter chi, a bridge between atomistic and mesoscopic simulation, was calculated based on atomistic simulation, taking into account the chemical constitution of UHMWPE/PA6 blends. It is found that these blends with differential mass fraction are preferentially aligned into parallel or perpendicular orientations with zero flow. When subjected to extensional (pressure-driven) flow, the aligned aggregates re-orient and these elongated aggregates are divided into discrete micelles, leading to the appearance of a thinner layer and a more homogeneous phase at a high pressure. In sharp contrast, when the mesoscopic behaviors were imposed by a shear flow over a series of shear rates, the blend systems preferentially form micelle-like structures at low shear rate, similar to the case under pressure-driven force, and transform to transverse lamella alignment with further increasing shear rate to <(gamma)over dot> = 0.1, which indicates that the shear flow not only induces the orientation of alignments, but also regulates the ordered distribution of aggregates.