Mobile Grafts Allow Polymers to Escape Confinement

Polymers attached to spherical particles are widely used in applications such as nanocomposites, drug delivery, and interfacial modification. In these systems, curvature-induced variations in monomer density lead to spatially dependent polymer chain structure and dynamics. Existing theories describing these effects assume that the polymer chains are anchored by immobile graft sites, but many experimental systems feature mobile or rearrangeable attachment points. Here, we use molecular simulations to show that the grafting site mobility significantly alters the dynamics of spherical polymer brushes. While both mobile and immobile grafts exhibit signatures of dynamic confinement near the particle surface, graft mobility reduces the extent of this confinement and shifts the crossover to unconfined dynamics. We quantify these effects through changes in the confinement length scale and the radial position at which confined dynamics disappears. In mixed systems, mobile grafts further facilitate the relaxation of neighboring immobile chains, establishing graft mobility as an important factor governing polymer dynamics in spherical polymer brushes.