Molecular dynamics simulation of entangled polymers in shear flow

Abstract

Large scale molecular dynamics simulation is conducted for a system of entangled polymers in shear flow. The polymer consists of 100, 200 and 400 beads, which is 3–10 times larger than the number of beads between the entanglement points. The simulation reproduces many characteristic features of the rheological properties of real polymeric liquids. The steady state viscosity $\text{η(}\text{γ}\text{̇}\text{)}$ plotted against the shear rate $\text{γ}\text{̇}$, approaches a power law curve $\text{η(}\text{γ}\text{̇}\text{)∼}\text{γ}\text{̇}{}^{\mathrm{-n}}$ which is independent of the molecular weight with the exponent n≃1. The second normal stress coefficient $\text{Ψ}{}_2\text{(}\text{γ}\text{̇}\text{)}$ is negative and its ratio to the first normal stress coefficient $\text{Ψ}{}_1\text{(}\text{γ}\text{̇}\text{), −Ψ}{}_2\text{/Ψ}{}_1$ approaches to zero with the increase of the shear rate. The bond orientation is measured as a function of the position of the bond along the chain, and the profile is consistent with the recent theory of Mead et al. for the convective constraint release.