Shear-induced martensitic transformations in crystalline polyethylene: Direct molecular-dynamics simulations

Abstract

For the first time, we carry out molecular dynamics (MD) simulation of shear-induced martensitic phase transitions between the orthorhombic and non-orthorhombic (triclinic and monoclinic) phases of crystalline polyethylene (PE) in the framework of a realistic all atom model of the polymer. We show that the variation of the shear rate allows observing on a nano-sample both a strongly nonequilibrium phase transition occurring by random nucleation and irregular growth of a new phase ('civilian' way, for rapid deformations) and the coherent, or 'military', kinetics (generally considered as usual for martensitic transformations). We induce transitions from the orthorhombic to the triclinic phase according to two transformation modes observed in experiment on PE single crystals. Rapid deformation favors the transition directly to the triclinic phase, slow deformation -first to the intermediate monoclinic, and only then -to the triclinic phase. The second way corresponds to the experiment on extended chain PE. We explain this result and analyze the competition between different transformation and plastic deformation modes. Rotations of PE chains around their axes necessary for the transition between the orthorhombic and non-orthorhombic phases are executed by short twist defects diffusing along the chains. The transition between the monoclinic and triclinic phases occurs through half-chain-period translations of the chains along their axes, mostly collectively, as crystallographic slips.

State Transitions and Crystalline Structures of a Single Polyethylene Chain: MD Simulations

“…57 Strelnikov et al investigated the shear-induced phase transition of crystalline polyethylene with the AMBER force field. 58 Sultanov et al investigated the phase transition of crystalline polyethylene during the heating process with the COMPASS force field. 59 Milner et al investigated the rotator phases of n-alkanes with the OPLS-AA force field.…”

“…Trigg et al investigated the crystalline structure of functional polyethylene chains with the LOPLS-AA force field . Strelnikov et al investigated the shear-induced phase transition of crystalline polyethylene with the AMBER force field . Sultanov et al investigated the phase transition of crystalline polyethylene during the heating process with the COMPASS force field .…”

Strongly localized wrinkling modes of single- and few-layer graphene sheets in or on a compliant matrix under compression

“…In general, we assume the orthorhombic symmetry of the compliant matrix, which can be a polyethylene crystal [31]. First we consider the graphene sheet placed in (001), z = 0, plane and the SAW propagates in the [100] direction.…”