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

Research output: Contribution to journalArticle

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.

Details

Authors
  • Pär Olsson
  • Per Hyldgaard
  • Elsebeth Schröder
  • Elin Persson Jutemar
  • Eskil Andreasson
  • Martin Kroon
Organisations
External organisations
  • Chalmers University of Technology
  • Tetra Pak AB
  • Linnaeus University
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Natural Sciences
  • Engineering and Technology

Keywords

  • Yielding, Martensitic phase transformations, Polyethylene
Original languageEnglish
Article number075602
Number of pages13
JournalPhysical Review Materials
Volume2
Issue number7
Publication statusPublished - 2018 Jul 10
Publication categoryResearch
Peer-reviewedYes