Abstract
Virtual experimentation involving atomistic simulation of a polyethylene melt undergoing elongational flow reveals a biphasic flow profile exhibiting a phase transition from an oriented liquid to a semicrystalline solid at high field strength. This flow-induced crystalline phase occurs at temperatures high above the quiescent melting point and appears to be reversible. A nonequilibrium phase diagram can be constructed exhibiting multiple stable and metastable states corresponding to coiled and stretched liquid states and semicrystalline solid phases with varying degrees of crystallinity and morphologies
Highlights
Of the 350 million tons of plastics produced worldwide during 2018, approximately one third were polyethylenes [1]
Such a suite of nonequilibrium molecular dynamics (NEMD) simulations would allow for the sampling of thermodynamic state points within temperature-stress parameter space, we limit the analysis to a single temperature within the liquid phase under quiescent conditions (450 K)
NEMD simulations were performed in the NV T statistical ensemble at 450 K and the experimental density of 0.766 g/cm3 using the Siepmann-Karaboni-Smit (SKS) united-atom potential model [51], which has been used by many research groups to study the quiescent and nonequilibrium structure and dynamics via molecular dynamics (MD) and MC of liquid and solid phase alkanes and PEs (e.g., [38,52,53,54,55,56])
Summary
Of the 350 million tons of plastics produced worldwide during 2018, approximately one third were polyethylenes [1]. Global revenues derived from plastics surpass half a trillion US dollars each year, with $150 billion due to polyethylene alone. These industries produce a huge variety of consumer goods ranging from simple household items to state-of-theart electronic components, including many high-performance composites used in applications of critical national need. The crystalline microdomains are formed by chain folding, wherein the long macromolecules fold back on themselves repeatedly, arranging into stacked structures called lamellae [2] These high-strength lamellar domains are surrounded by amorphous regions of entangled polymer chains that provide flexibility and thermal/electrical resistance to the semicrystalline material
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