Ab initio investigation of monoclinic phase stability and martensitic transformation in crystalline polyethylene

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Abstract

We study the phase stability and martensitic transformation of orthorhombic and monoclinic polyethylene by means of density functional theory using the nonempirical consistent-exchange vdW-DF-cx functional [Phys. Rev. B 89, 035412 (2014)]. The results show that the orthorhombic phase is the most stable of the two. Owing to the occurrence of soft librational phonon modes, the monoclinic phase is predicted not to be stable at zero pressure and temperature, but becomes stable when subjected to compressive transverse deformations that pin the chains and prevent them from wiggling freely. This theoretical characterization, or prediction, is consistent with the fact that the monoclinic phase is only observed experimentally when the material is subjected to mechanical loading. Also, the estimated threshold energy for the combination of lattice deformation associated with the T1 and T2 transformation paths (between the orthorhombic and monoclinic phases) and chain shuffling is found to be sufficiently low for thermally activated back transformations to occur. Thus, our prediction is that the crystalline part can transform back from the monoclinic to the orthorhombic phase upon unloading and/or annealing, which is consistent with experimental observations. Finally, we observe how a combination of such phase transformations can lead to a fold-plane reorientation from {110} to {100} type in a single orthorhombic crystal.

Detaljer

Författare
  • Pär Olsson
  • Per Hyldgaard
  • Elsebeth Schröder
  • Elin Persson Jutemar
  • Eskil Andreasson
  • Martin Kroon
Enheter & grupper
Externa organisationer
  • Chalmers Tekniska Högskola
  • Tetra Pak AB
  • Linnaeus University
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Naturvetenskap
  • Teknik och teknologier

Nyckelord

Originalspråkengelska
Artikelnummer075602
Antal sidor13
TidskriftPhysical Review Materials
Volym2
Utgåva nummer7
StatusPublished - 2018 jul 10
PublikationskategoriForskning
Peer review utfördJa