Molecular Dynamics Simulation on Static and Rheological Properties of Polymer-Nanoparticle composite Systems with Chemically Identical Brush and Matrix chains

Polymer grafted nanofillers are widely used to reinforce the polymer matrix. Recently, Giovino et al. (Giovino M, Pribyl J, Benicewicz B, Kumar S, Schadler L, Polymer 2017, doi: 10.1016/j.polymer.2017.10.016.) studied the rheology of the polystyrene(PS)-grafted silica NPs mixed with the PS matrices of different chain lengths in experiment. They found the relative viscosity increase caused by the NPs in the system with shorter PS chains was much greater than that caused by the NPs in the system with longer PS chains, while the dispersion states of NPs and glass transition temperatures were very similar. To expose the mechanism responsible for the behavior, we used molecular dynamics to simulate nanocomposite systems with chemically identical brush and matrix chains. The viscosity increases observed in our simulations exhibit similar trends as those in the experiment. However, we find that the brush chain conformation undergoes a transition from self-avoiding walk to ideal Gaussian when the matrix chain length is of the order of square root of the grafted chain length, indicating that in the experimental studies the brush chains were Gaussian. To further expose the specifics of reinforcement mechanism, we evaluate microscopic effects of grafted NPs on the dynamics of matrix chains.