Molecular Simulations of Ultra - Con fi ned Polymers . Polystyrene Intercalated in Layered - Silicates

Molecular Dynamics simulations are used to explore the structure and dynamics of polystyrene confined in 2nm slit pores, between surfactant-bearing mica-type surfaces. The systems simulated resemble experimentally studied intercalated nanocomposites, where polystyrene is inserted between alkyl-ammonium modified fluorohectorite silicate layers. The molecular modeling perspective complements the experimental findings and provides insight into the nature of polymers in nanoscopic confinements, especially into the molecular origins of their macroscopic behavior. Namely, simulations show a distribution of relaxations, ranging from extremely faster and to much slower segmental motions than the ones found in the corresponding bulk polymer at the same temperature. The origins of these dynamical inhomogeneities are traced to the confinement induced density modulations inside the 2nm slits. Fast relaxing phenyl and backbone moieties are found in low density regions across the film, and preferentially in the center, whereas slow relaxing moieties are concentrated in the denser regions, especially in the immediate vicinity of the confining surfaces.