Hydrodynamic correlations and diffusion coefficient of star polymers in solution.

Abstract

The center-of-mass dynamics of star polymers in dilute solution is analyzed by hybrid mesoscale simulations. The fluid is modeled by the multiparticle collision dynamics approach, a particle-based hydrodynamic simulation technique, which is combined with molecular dynamics simulations for the polymers. Star polymers of various functionalities are considered. We determine the center-of-mass velocity correlation functions, the corresponding mean square displacements, and diffusion coefficients. The velocity correlation functions exhibit a functionality-dependent and structure-specific intermediate time regime, with a slow decay. It is followed by the long-time tail t(-3/2), which is solely determined by the fluid. Infinite-system-size diffusion coefficients are determined from the velocity correlation function by a combination of simulation and analytical results, as well as from the center-of-mass mean square displacement for various systems sizes and extrapolation. In terms of the hydrodynamic radius, the star polymer hydrodynamic diffusion coefficient exhibits the same universal system-size dependence as a spherical colloid. The functionality dependence of the ratio of hydrodynamic radii and the radii of gyration agrees well with experimental predictions.