(338g) Structure and Rheology of Polymer Solutions from Coarse-Grained Molecular Dynamics Simulations: Effects of Polymer Concentration, Solvent Quality and Geometric Confinement
Structure, dynamics and rheology of solutions of flexible linear polymers are investigated using coarse-grained (CG) molecular models and molecular dynamics (MD) simulations in presence of explicit solvent mediated interactions. MARTINI force field is employed to describe the polymer, solvent and the underlying physico-chemical interactions. The CG models are validated against atomistic ones by comparing the predictions of certain structure parameters such as persistence length, radius of gyration and radial distribution functions of the monomeric units. First, we will present results for the dynamics of a single polymer chain in shear flow. The effects of chain length and shear rate on the configuration statistics, e.g. tumbling frequency and orientation distribution of the end-to-end vector, will be presented and compared to experimental observations and predictions of stochastic dynamics simulations. Further, the effects of solvent-polymer interactions under good, theta and poor solvent conditions as well as geometric confinement in presence of favorable, neutral and unfavorable polymer-wall interactions on the configuration dynamics of a single polymer chain will be also discussed. Specifically, the role of solvent quality will be shown to have a pronounced effect on coil-stretch transition in shear flow. CGMD predictions for the relationship between the zero-shear viscosity and polymer concentration in dilute and semi-dilute regimes will be presented and compared to experiment results. Shear thinning behavior is observed in both dilute and semi-dilute solutions in non-equilibrium molecular dynamics simulations. Possible approaches using MD simulation data to parameterize phenomenological constitutive models such as the Carreau-Yasuda model will also be discussed. (Support from the National Science Foundation through grants CBET-1055219 and CDI 1049489 is gratefully acknowledged).