Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

Abstract

Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those for thermal welding of homopolymer slabs. The two processes differ in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface. The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the interdiffusion is significantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of them are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and thus mechanically weaken the interface. When the interfacial strength saturates, the number of interfacial entanglements scales with the corresponding bulk entanglement density. Chain stiffness increases the density of entanglements, which increases the interfacial strength. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.

Phys. Rev. E (in press)

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Cited by in corpus (7)

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• Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
• Relating Chain Conformations to Extensional Stress In Entangled Polymer Melts
• Characteristic time and length scales in melts of Kremer-Grest bead-spring polymers with wormlike bending stiffness
• Crazing of Nanocomposites with Polymer-Tethered Nanoparticles
• Super-stretchable Elastomer from Cross-linked Ring Polymers
• O'Connor, Alvarez, and Robbins Reply to Xu et al. (arXiv:1808.05390)