Multiscale modeling of polystyrene in various environments

We develop a systematic multiscale modeling approach for understanding the dynamics of polystyrene in the melt and blended with polyisoprene. The dynamics of polystyrene chains at chain length of 15 monomer in both environments are investigated using both atomistic and mesoscale models. The dynamics of polystyrene with chain length of 30 monomers and longer are illustrated by mesoscale models. The iterative Boltzmann inversion (IBI) method is used to derive the mesoscale models based on the atomistic simulations. The polystyrene chains clearly show dynamical heterogeneity along the chain and among chains in both models. The reorientation of PS chains speeds up with the increase of PI in the blends. We observe the onset of phase separation in atomistic simulations of polyisoprene-polystyrene blends at chain length of 15 monomer, and find full phase separation using mesoscale models for blends with chain length of 30 and above. We show that phase separation cannot be achieved with simple mixing rules. The phase separation morphologies could be cylindrical or spherical depending on the concentration ratio of the two components. The densities of the blends and their temperature dependencies are characterized.