Molecular dynamics simulations of polystyrene brushes in dry conditions and in toluene solution.

The properties of polystyrene brushes in dry conditions and in toluene solution are studied as a function of grafting density using molecular dynamics simulations. Both, individual brushes and double layers of opposing brushes are considered, the structural properties of which were found to be similar. The density profiles show very pronounced density oscillations which extend up to approximately 1.8 nm and fall into two groups of three peaks each. These features are observed regardless of grafting density and solvent conditions. In the absence of solvent, the chains undergo a transition from an oblate to a spherical shape as the grafting density increases. In contrast, in good solvent, the chains remain spherical independent of the grafting density. Solvation also increases the extension of the polystyrene chains roughly by a factor 2.5. Isotropic and two-dimensional radial distribution functions are used to characterize the structure of the polystyrene brushes. Toluene is observed to form up to four layers at the base of the grafted chains irrespective of grafting density.