Simulating Polymer Behavior in Silica Nanocomposites

Polymer chain behavior in polymer/silica nanocomposites was explored using long-term atomistic molecular dynamics simulations. The study focused on two polymers: poly-(butadiene) (PB) and poly(ethylene oxide) (PEO). Both cis-1,4-PB and trans-1,4-PB nanocomposite systems contain 30 wt% silica nanoparticles with a diameter of about 4 nm. The overall size of the PB polymer chains remained unaffected, except for a small number of chains that wrapped around the nanoparticles. However, both the segmental and terminal dynamics of the PB chains were found to be slower in the nanocomposites compared to the corresponding bulk melts. Additionally, the PB chains within the nanocomposites exhibited highly heterogeneous dynamics, and a coupling between the dynamics and the conformation of PB chains was observed.

In the case of PEO nanocomposites, the effects of chain adsorption and the spatial confinement from the nanoparticles on the polymer's structure and dynamics were investigated. The analysis of static properties showed a heterogeneous polymer density layer near the interface of the PEO and silica. For systems with a low volume fraction of silica nanoparticles, a thin layer of slow-moving polymer chains forms on the nanoparticle surface. The polymer chains farther away from the surface move similar to a bulk material system. Conversely, in systems with a high volume fraction of nanoparticles, the dynamics of all the PEO polymer chains were predicted to be slower than in the bulk due to a strong confinement effect.