The welding of two molten polyethylene films followed by their crystallization is studied using molecular dynamics simulations. The melts are composed of chains with either 200 or 2000 coarse-grained ethylene monomers, i.e., two carbons and their associated hydrogens lumped into a single bead. During melt welding, orientational and entanglement inhomogeneities caused by the preexisting film surfaces are resolved on molecular diffusion timescales. Crystallization of partially interdiffused films strongly amplifies the residual melt orientational anomalies, leading to higher crystallinity near the weld line. This phenomenon is unique to semicrystalline polymers and is expected to cause long-lived inhomogeneities in the structure of the welded interfacial region.

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• Anomalous diffusion
• Crystallization
• Interface & surface thermodynamics
• Nonequilibrium & irreversible thermodynamics
• Polymer entanglement
• Polymer folding
• Linear polymer
• Polymer melts
• Polymer thin films
• Semicrystalline polymers
• Coarse graining
• Molecular dynamics