Slow relaxations of grafted polymer due to confinement by neighboring chains

The behavior of nanoparticles dispersed in solutions plays a crucial role in environmental remediation, nanocomposite processing, and targeted drug delivery methods. These applications require well-dispersed particles, commonly achieved by grafting polymers to the particle surface. This end-tethered topology leads to strong deviations in the properties of grafted chains compared to those of free chains. Using neutron scattering techniques, we directly measure the structure and dynamics of grafted polymer chains in semidilute solutions. The grafted polymer relaxations initially follow the Zimm model but are slower than expected at longer time scales. These slow dynamics are caused by the confinement of neighboring chains, underscoring the importance of grafting on the dynamic properties of grafted polymers. Further, we disperse the grafted nanoparticles into solutions of linear polymers that act as crowding agents to compress the grafted corona. As the corona densifies due to an increase in osmotic pressure, the grafted polymers become more confined and exhibit slower relaxations. We identify grafting density as a crucial variable controlling the relaxations of grafted polymers and demonstrate that transverse and lateral relaxations decouple even at moderate grafting densities.