Molecular Dynamics Study of a MARTINI Coarse-Grained Polystyrene Brush in Good Solvent: Structure and Dynamics

We use a newly developed model of polystyrene, based on the MARTINI coarse-grained force field, to study the behavior of polystyrene brushes in benzene via molecular dynamics simulations. We focus on chain lengths comparable to those accessible experimentally. We analyze the structural and dynamical configuration of the brushes as a function of their grafting density in a high: grafting density regime (0.1-0.3 chains nm(-2)). Only the highest density brush considered here (0.3 chains nm(-2)) turns out to be characterized by a well-defined bulk area, where the density profile is flat, the lateral pressure profile has a plateau, and the chains are aligned perpendicularly to the substrate. At all grafting densities, our simulations reveal the presence of metastable collapsed states, with free chain ends trapped close to the substrate. These collapsed states are shown to be long-lived, surviving over a time scale of several microseconds.