Multiscale Polymer and Nanoparticle Dynamics in Attractive Polymer Nanocomposite Melts

The addition of nanoparticles (NPs) to a polymer matrix, forming a polymer nanocomposite (PNC), has been used to extend and control macroscopic material properties. Many macroscopic properties are dictated by microscopic dynamic processes, including the dynamics of the polymer segments, chains, and NPs, which remain poorly understood in PNCs. This work experimentally explores the hierarchy of dynamics in model PNC melts with poly(2-vinylpyridine) and attractive NP-polymer interactions. In PNCs with 26-nm diameter NPs, we show that a bound polymer layer forms in solution and persists to the melt state. Using various techniques, we report that segmental relaxations near the NP interface are slower than in neat polymer and lead to polymer chain desorption that is ~10⁴ times slower than bulk diffusion. Interestingly, when the NP size is commensurate with the polymer segments (~2 nm), the dynamics are quite different. For example, polymer segments are slowed homogeneously, slow chain diffusion is quantitatively described by increased segmental friction, and the NPs diffuse anomalously fast. Overall, these results highlight the complex and synergistic effects of NPs and polymers in PNCs and provide insights to help design functional PNCs for a variety of applications.