Nanoscale Structure-Property Relations in Self-Regulated Polymer Grafted Nanoparticle Structures

Using a model system of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NP) and poly(styrene-ran-acrylonitrile) (SAN), we generated unique polymer nanocomposite morphologies by balancing the degree of phase separation and wetting within the films. Depending on the annealing temperature, the thin films undergo different stages of phase evolution, resulting in homogenously dispersed systems at low temperatures and three-dimensional bicontinuous structures of PMMA-NP pillars sandwiched between two PMMA-NP wetting layers at high temperatures. Using a combination of atomic force microscopy (AFM), AFM nanoindentation, and optical microscopy, we show that these self-regulated structures lead to nanocomposites with increased modulus, hardness, and thermal stability compared to analogous PMMA/SAN blends. These studies demonstrate the ability to reliably control nanocomposite surface morphologies, which have attractive technological applications where surface-dependent properties such as wettability, durability, and the friction are important.