Effects of Film Thickness and Nanoparticle Loading on Surface Wetting of Grafted Nanoparticles in Polymer Nanocomposites

Polymer nanocomposites (PNCs) allow for a broad range of applications owing to their versatile properties, which are directly correlated to the spatial arrangement of the nanoparticles in the polymer matrix. For instance, surface properties such as wettability, friction, and durability depend on the wetting behavior of nanoparticles in PNCs. Previously, we determined the diffusion coefficient of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NPs) in a poly(styrene-ran-acrylonitrile) (SAN) matrix using time-of-flight secondary ion mass spectrometry (ToF-SIMS). In this work, we continue to study the effect of film thickness and nanoparticle loadings on the PNC structure and PMMA-NP diffusion in SAN using ToF-SIMS, along with techniques such as atomic force microscopy and grazing-incidence small-angle x-ray scattering. To decouple the surface and thermodynamic contributions, we investigate the effect of confinement on PNC structure using films with a thickness from 100 to 1500 nm. By adding 10 wt.% of PMMA-NPs to SAN compared to prior studies with 25 wt.%, we study how decreased NP loadings affect nanoparticle diffusion to the surface. The results allow for greater control over NP dispersions and PNC morphologies, which are crucial in tailoring PNC properties.