Molecular Dynamics Simulations of a Polymer Star under Shear Flow

We performed large-scale coarse-grained molecular dynamics simulation of a polymer star in a melt of short polymer chains under shear flow in dilute star concentrations. The temperature of the system was maintained using a dissipative particle dynamics (DPD) thermostat to conserve momentum and model hydrodynamic interactions. Simulations at the quiescent state was used to determine the timescale for which the end-to-end vector of the star’s arm as it relaxes. The star has sixteen arms and its motion under shear in high Weissenberg numbers is characterized by a cycle of collapse and extension of the star’s arm, which is in line with expected tank-treading motion. We used the trajectories of these simulations to calculate quantities pertinent to neutron scattering experiments, such as small angle neutron scattering under high shear stress, or SANS in the rheo-SANS environment, and predict the resulting spectra from these experiments. Specifically, we calculate the star’s anisotropic single-molecule structure factor through the spherical harmonic expansion approach.