Using Time-of-Flight Secondary Ion Mass Spectrometry to Study Surface Wetting of Nanoparticles in Polymer Nanocomposites

Polymer nanocomposites (PNCs), a combination of inorganic and organic fillers in polymer matrices, are of considerable interest because of their versatile properties. Specifically, the wetting behavior of nanoparticles (NPs) can enhance surface properties, such as wettability, friction, and durability. In our work, we utilize time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate the wetting of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NPs) in a poly(styrene-ran-acrylonitrile) (SAN) matrix. To useToF-SIMS, experimental parameters such as incident beam energy and current as well as charge compensation are optimized to maximize secondary ion yields and minimize sample damage. From ToF-SIMS depth profiles, the PMMA-NP surface excesses (Z^*) are measured as a function of annealing time, allowing for the determination of the mutual diffusion coefficient. By varying the molecular weights of PMMA grafted chains and film thicknesses, we study how diffusion of PMMA-NPs in SAN depends on NP sizes and PNC film thicknesses, respectively, aiming to elucidate a morphology map for the PNC system. The results allow for greater control over NP dispersions and PNC morphologies, which are crucial in tailoring PNC properties.