Molecular dynamics simulations of extensional, sheet and unidirectional flow

Abstract Non-equilibrium molecular dynamics, NEMD, has been used to determine the technologically important tensile viscosities. Simulations of elongational, sheet and unidirectional viscoelastic responses via the “differences-in-trajectories” technique have been made on Lennard-Jones liquid at ϱ* = 0.8442 and T * = 0.72, and ϱ* = 1.01304 and T * = 1.26. At finite strain rates (·γ* ≥ 0.1) shear thinning behavior is evident, in particular for unidirectional (“poker chip”) extensional flow. At γ ≥ 0.4 steady state unidirectional viscosities were not achieved before severe material deterioration. These trends are the result of extremely complex structural reorganisation well within the viscoelastic regime, which involved coupled component relaxation moduli along distortion direction.