Conformation and Dynamics along the Chain Contours of Polymer-Grafted Nanoparticles

Densely grafted polymer chains onto spherical nanoparticlesproducea diverse range of conformations. At high grafting densities, thecorona region near the nanoparticle surface undergoes intense confinementdue to a high concentration of chains in the concentrated polymerbrush (CPB) region, which results in strong stretching for portionsof the chains located within. In contrast, a semi-dilute polymer brush(SDPB) forms farther away from the core and offers reduced confinementfor the polymer and more ideal conformations. However, conventionalexperimental methods are limited in their ability to provide detailedinformation on individual segments of grafted polymers in these regions;hence, molecular dynamics (MD) simulations are essential for gainingcomprehensive insights into the behavior of the grafted chains. Thisstudy aims to explore the variations in polymer structure and dynamicsthat occur along the contour of the grafted chains as influenced byspatial confinement. We focus on the motions and relative positionsof each bead along grafted polymers. Our results show that only theinitial few grafted beads near the nanoparticle surface exhibit thestrong stretching attributed segments in the CPB region of the brush.Increased grafting density or decreased chain flexibility leads tomore stretched grafted chains and more aligned bond vectors. As aresult, the relaxation dynamics of local regions of the polymer arealso strongly influenced by these parameters. Although the graftedbeads in the interior of the CPB region are highly sensitive to theseparameters, those farther from the nanoparticle core experience significantlydiminished effects. In comparison to the Daoud-Cotton (DC)model's predictions of CPB size, beads near the nanoparticlesurface show slower dynamic decay, especially in high grafting densities,aligning with the DC model's estimates. Finally, we compareour simulations to previous works for additional insight into polymer-graftednanoparticles.