(284b) Dynamics of Polymer-Grafted Nanoparticles Under Soft Confinement
We graft high molecular weight polystyrene (Mw = 355 kDa, Rg = 21 nm) to the surface of comparably sized silica nanoparticles (R = 24 nm) using a âgrafting-toâ synthetic route with âclickâ chemistry. Thus, these PGNPs are in the intermediate regime where both the finite core and polymer chain flexibility affect the controlling physics. We then disperse the PGNPs in semidilute solutions of linear polymer with molecular weights of 138, 656, and 1114 kDa. Exploiting the differences in scattering length densities, we probe the dynamics and structure of PGNPs on the nano- and microscale with complementary x-ray and neutron scattering methods. The PGNPs undergo structural changes like those of other soft colloids, but their dynamics are distinct. In the presence of free polymer, the grafted polymers compress because of an increase in the osmotic pressure of the solution, in agreement with earlier studies on polymers with complex architectures. The dynamics of the grafted polymer are confined by the neighboring polymer chains and become more confined as the grafted corona compresses. Additionally, the dynamics of the PGNPs through the polymer solutions decouple from the bulk solution viscoelasticity despite the PGNP hydrodynamic radius being much larger than that of the free polymer. These novel dynamics illustrate the physical complexity underlying the structure and dynamics of PGNPs, especially when dispersed in structured fluids. With this work, we identify how the structure and dynamics of PGNPs respond to complex environments, such as those found in materials processing and biological applications. The changes in the dynamics of grafted polymers and the polymer-grafted nanoparticles will be important to designing improved composite materials and targeted drug delivery vectors.