Linear viscoelastic behavior of unentangled polymer melts via non-equilibrium molecular dynamics

We present and assess the use of non-equilibrium molecular dynamics (NEMD) simulation method for the direct study of the linear viscoelastic behavior of polymer melts. The polymer melt is modeled by a collection of repulsive, anharmonic multibead chains subjected to small amplitude oscillatory shear flow. We present results for chain lengths below the critical entanglement length and obtain good agreement with theoretical results for the viscoelastic behavior of melts of low molecular weight. The range of oscillation frequencies attainable in the simulation is of a few decades. Thus we use, as in experiments, a time-temperature superposition rule to extend the frequency domain. As a side result, we confirm the so-called Cox-Merz rule.