Insight into the Dispersion Mechanism of Polymer-Grafted Nanorods in Polymer Nanocomposites: A Molecular Dynamics Simulation Study

Abstract

Coarse-grained molecular dynamics simulations are performed to investigate the dispersion behavior and the underlying dispersion mechanism of polymer-grafted nanorods (NRs) in a polymer matrix. The influences of grafting density, grafted chain length, and the miscibility between grafted chains and matrix chains are systematically analyzed. The simulation results indicate that the dispersion state of grafted NRs is determined primarily by the excluded volume effect of grafted NRs and the interface between grafted chains and matrix chains. It is found that increasing grafting density and/or grafted chain length induces the conformational transition of grafted chains from mushroom to brush, enlarges the excluded volume of grafted NRs, and enhances the brush/matrix interface in the brush regime, resulting in the improvement of the NR dispersion state. By tuning the interaction strength between grafted chains and matrix chains in a wide range, three general categories of NR spatial organization are found: macroscopic phase separation of the NRs and polymer matrix, homogeneous dispersion of the NRs, and “tele-bridging” of the NRs via the matrix chains. The transition from a “wet” to “dry” brush is observed at the strong brush/matrix interaction. In addition, for the polymer brush grafted on the surface of NRs, the dependence of the brush thickness Tb on either grafting density Σ or grafted chain length Lg is always weaker than that of polymer brush grafted on flat surface or spherical surface, mainly due to the broader range of moving and the less stretching of polymer chains grafted to NRs. The Tb scales with Σ and Lg as Tb ∼ ΣαLgβ, where the ratio β/α is a constant equal to 3, independent of the grafted surface. In general, this work offers a deep insight into the dispersion mechanism of grafted NRs and thus is believed to provide some guidance on the design and preparation of high-performance polymer nanocomposites with tailored dispersion of NRs.