Molecular Simulations of Passive Particle Rheology

In this work, we demonstrate that nanoscale viscoelastic properties of polymer melts can be obtained from molecular dynamics (MD) simulations by using an approach analogous to the experimental passive microrheology. We carry out MD simulations of a system consisting of a probe particle that is embedded in a polymer melt represented using the bead-spring model. The mean squared displacement of the probe particle determined from these MD simulations is analyzed to calculate the storage and the loss moduli of the medium. Our results indicate that calculation of the viscoelastic properties from the straightforward Generalized Stokes Einstein Relationship leads to unphysical values for these quantities in the high frequency regime. We show that this problem can be alleviated by accounting for the inertial effects in the system. Our particle rheology simulation results are quantitatively compared with the literature results that were obtained from other simulation approaches. Results will also be presented for the effects of the particle size, rigidity and the chain length on the viscoelastic properties.