Conformations and Dynamics of Polymer Chains in Cis and Trans Poly(butadiene)/Silica Nanocomposites through Atomistic Simulations: From the Unentangled to the Entangled Regime*

We present a detailed investigation of the
conformations and the dynamics of cis and trans poly(butadiene) (PB) chains in PB/spherical-silica nanocomposites, through long time atomistic molecular dynamics simulations at 413 K, well above T_g.
PB chains of different lengths, covering the range from the unentangled to the mildly entangled regime are analyzed.
The systems contain 30 wt % (≈ 12 vol %) silica NPs of diameter ≈ 4 nm.
The nanocomposites are studied through analyzing: (i) interfacial packing and the dimensions of the PB chains; (ii) statistics of the train, bridge, loop, and tail conformations and the coupling between segmental orientational dynamics and chain conformations; (iii) the orientational and translational dynamics of the polymer chains, and the desorption kinetics of chains and segments.
The dimensions of PB chains, excluding a small fraction of chains that wrap
around the NP, are not modified.
The segmental and terminal dynamics of PB chains slow down in the nanocomposites. At long times, bridge segments, exhibit a slow orientational decorrelation.
The correlation times for the desorption of segments and chains, are much larger
than the segmental and end-to-end-vector correlation times, respectively.