Interface and Interphase Dynamics of Polystyrene Chains near Grafted and Ungrafted Silica Nanoparticles

The chain and segmental dynamics of free and grafted 20-monomer atactic polystyrene chains surrounding a silica nanoparticle have been investigated employing atomistic molecular dynamics simulations. The effect of the nanoparticle curvature and grafting density on the mean square displacement of free polystyrene chains and also on the mean relaxation time of various intramolecular vectors was investigated as a function of separation from the surface. Confinement, reduced surface curvature, and densification resulted in a reduction of the mean square displacement and an increase in the mean relaxation time of the Cα–H bond vector and chain end-to-end vector in the vicinity of the surface. Depending on the property investigated, the thickness of the interphase, i.e., the distance beyond which the polymer has bulk behavior, varies between 1 and 3 nm, corresponding to 1–3 radii of gyration of the bulk polymer. Therefore, the presence of a surface has a significant influence on the dynamics of the surrounding polymer chains especially the ones in the interfacial region.