A jamming morphology map of polymer blend nanocomposite films

The addition of nanoparticles (NPs) to polymer blends is an attractive route for controlling their morphology. Here, we investigate the phase separation of poly(methyl methacrylate) (PMMA) : poly (styrene-ran-acrylonitrile) (SAN) films with thicknesses from 140 nm to 2500 nm and silica NP concentrations from 1 to 10 wt%. Atomic force microscopy (AFM) and focused ion beam (FIB) etching combined with scanning electron microscopy (SEM) are used to identify the morphology as discrete or bicontinuous. FIB/SEM is introduced as a facile method to locate NPs at the PMMA/SAN interface and construct 3D images of the morphology of thick films. With increasing film thickness, the concentration of NPs required to stabilize a bicontinuous morphology decreases from 10 wt% to 2 wt%. A jamming map of the discrete and bicontinuous morphologies is constructed to examine the interplay between NP concentration and film thickness. The delineation between these jammed morphologies agrees with a simple geometric model based on arranging spherical NPs at the PMMA/SAN interface. The bicontinuous morphology is an especially attractive structure for applications requiring high interfacial area such as organic solar cells, membranes, catalysis, and fuel cells.