Polymer segmental dynamics near the interface of silica particles in the particle/polymer composites

We demonstrate an approach to examine the local segmental dynamics of a polymer near the interface of an inorganic filler by observing the rotational dynamics of the fluorescent probe at the chain ends of poly-mer brushes grafted onto the surface of the filler particles. Localization of the fluorescent probe was real-ized by designing and synthesizing fluorophore-tethered polystyrene (PS) brushes anchored on the surface of silica particles of controlled sizes. Fluorophore-functionalized telechelic PS with an azide func-tionality at the other chain end was achieved via a combination of atom transfer radical polymerization and post-polymerization modification. The azide-bearing PS chains were tethered to alkyne-functionalized particles via copper-catalyzed cycloaddition reaction. The molecular weight of the grafted polymer chains was controlled to be less than the critical entanglement molecular weight, and the chain density was controlled to be low enough so that the observed dynamics was not perturbed by the poly-mer brush conformation and brush-matrix polymer entanglement. The polymer dynamics near the sur-face of the particles at low concentrations was closely examined in the bulk film geometry by employing imaging rotational fluorescence correlation microscopy (irFCM). The observed polymer dynamics near the interface were not altered in the inorganic/polymer composite geometry when the surface did not have favorable interaction with the matrix polymer. The presented rational design of the chemical route and examination of local dynamics highlight a feasible approach to construct material systems with high complexities towards a deeper understanding of composite materials.

Automated summary

In this study, an approach to examine local segmental dynamics of a polymer near the interface of an inorganic filler was demonstrated by observing the rotational dynamics of fluorescent probes attached to the ends of polymer brushes. The localization of the probes was achieved by designing and synthesizing fluorophore-tethered polystyrene brushes on the surface of controlled-sized silica particles. By controlling the molecular weight and density of the grafted polymer chains, the observed dynamics were not affected by the polymer brush conformation and brush-matrix polymer entanglement. It was found that the polymer dynamics near the interface in the inorganic/polymer composite geometry remained unchanged when there was no interaction between the surface and the matrix polymer.