Nanoparticle Diffusion as a Function of Polymer Molecular Weight and Bound Layer Dynamics

The bound layer is characteristic of attractive polymer nanocomposites (PNCs) and contributes to improved nanoparticle (NP) dispersion and nanocomposite processing. However, the dynamics of bound layer exchange with the matrix are challenging to probe due to the lack of contrast between the bound and matrix polymers. Here, we probe NP diffusion across a variety of NP sizes (alumina, silica) and poly(2-vinylpyridine) (P2VP) molecular weights using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). With increasing R_g:R_NP (~0.5 to 3), the mode of polymer diffusion transitions from core-shell to vehicle. The strength of NP-polymer interaction is tuned using PS-co-P2VP copolymers. Our findings confirm the bound layer has strong influence on NP diffusion and establish NP diffusion as a method for exploring bound layer dynamics in attractive PNCs.