Hugoniostat and Direct Shock Simulations in cis‐1, 4‐Polybutadiene Melts. Issue 2 (16th December 2020)

• Record Type: Journal Article
• Authors: Lecoutre, Gautier; Lemarchand, Claire A.; Soulard, Laurent; Pineau, Nicolas
• Is Part Of: Macromolecular theory and simulations. Volume 30:Issue 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-16
• Subjects: glass transition -- molecular dynamics -- polymer melt -- shear stress relaxation -- shock; Macromolecules -- Periodicals; Polymers -- Periodicals; Polymerization -- Periodicals; Macromolécules -- Périodiques; 547.705
• DOI: 10.1002/mats.202000068
• Languages: English
• ISSNs: 1022-1344

Abstract

Abstract: The non‐reactive OPLS‐AA force‐field is used to compare direct shock and Hugoniostat simulations of a melt of cis‐1, 4‐polybutadiene at different shock velocities and with chain lengths up to 500 monomers. Both methods yield equivalent Hugoniot data with negligible influence of the chain length. However, it is found that the dynamical compression effects induce a time‐dependent anisotropy in the stress tensor in the direct shock simulations, yielding a non‐zero shear component. This anisotropy vanishes to the usual isotropic stress through two specific relaxation mechanisms: a fast process (characteristic time ≈1 ps) associated with the relaxation of the local intramolecular degrees of freedom of the chains, and a second slower process (characteristic time ≈100 ps) associated with the structural reorganisation of the polymer chains, involving long‐range intramolecular and intermolecular interactions. A third potential relaxation process, associated with entanglements, may be at play but is beyond the scope of the present study. Abstract : Direct shock and Hugoniostat simulations of a polymer melt are compared at different shock velocities and chain lengths. Both methods yield equivalent Hugoniot data. However, while the Hugoniostat method predicts an isotropic stress far behind the shock front, the direct shock simulations show a time‐dependent shear stress, which is modeled by a Prony series as a viscoelastic fluid.