Structure and Dynamics of Polymer Segments in Polymer-Grafted Nanoparticle Melts

We present an extensive coarse-grained molecular dynamics study of polymer-grafted nanoparticle (GNP) melts, focusing on the structure and dynamics of the grafted polymers by systematically varying grafting density and chain length. Consistent with theoretical predictions from the recently established two-layer GNP model, we observed the formation of a self-monomer-rich dry layer near the nanoparticle (NP) surface that limits interchain mixing from neighboring GNPs. Beyond this region, an interpenetration layer forms with significant chain mixing. At fixed chain length, the degree of interchain mixing decreases with increasing grafting density, leading to a more extended dry layer at the expense of the interpenetration layer. Segmental analysis shows pronounced chain stretching within the dry layer, while segments adopt coil-like conformations within the interpenetration layer. At high grafting densities, the relative stretching of chain segments becomes nonmonotonic, with a maximum near the center of the interpenetration layer. The bond vector autocorrelation function, which probes segmental dynamics, exhibits a saturation plateau for bonds near the NP surface, reflecting persistent confinement and restricted mobility due to the dense grafting environment. This plateau gradually disappears with an increasing distance of the bonds from the NP surface, and the bond dynamics instead exhibits a power-law decay characteristic of Rouse dynamics in bulk polymer melts. These findings highlight the spatially heterogeneous nature of chain conformations and mobility within the grafted corona.