Atomistic Simulation Studies of Polymer / Silica Nanocomposites

The conformations and the dynamics of polymer chains in polymer/silica nanocomposites are studied through atomistic molecular dynamics simulations. Two polymers have been utilized: A) Poly(butadiene), where the effect of the stereochemistry of PB chains is addressed by simulation of cis-1,4-PB/silica and trans-1,4-PB/silica nanocomposites. The model systems contain 30wt % silica nanoparticles. The dimensions of PB chains, excluding a small fraction of chains that wrap around the NP, are not affected. The dynamics of PB chains in the nanocomposites is very heterogeneous and a coupling between the dynamics and the conformation of PB chains is observed. B) Poly(ethylene oxide), where the effect of spatial confinement, induced by the nanoparticles on the polymer structure and dynamics is studied. Investigation of the static properties of the nanocomposites reveals a heterogeneous polymer density layer at the vicinity of the interface. For small volume fraction of silica nanoparticles, the polymer dynamics is consistent with the presence of a thin adsorbed layer of slow dynamics which attains the bulk dynamics far away from the nanoparticle. For high volume fraction of nanoparticles (strong confinement) the dynamics of all polymer chains are predicted slower than that in the bulk.