Segmental Dynamics in PMMA-Grafted Nanoparticle Composites

Abstract

We have recently shown that silica nanoparticles grafted with polystyrene chains behave akin to block copolymers due to the “dislike” between the nanoparticles and the grafts. These decorated nanoparticles, thus, self-assemble into various morphologies, from well-dispersed nanoparticles to anisotropic superstructures, when they are placed in homopolystyrene matrices of different molecular masses. Here, we consider a slightly different case, where the grafted chains and the matrix (both PMMA) are strongly attracted to the silica nanoparticle surface. We then conjecture that these systems show phase mixing or demixing depending on the miscibility between the brush and matrix chains (“autophobic dewetting”). At 15 mass % particle loading, composites created using the same grafted nanoparticle, but with two different matrices, yield well dispersed nanoparticles or nanoparticle “agglomerates”, respectively. Rheology experiments show that the composites display solid-like behavior only when the particles are ag...