Phase Behavior of Polymer-Grafted Nanoparticles in Homopolymer Blends from Simulations

The phase behavior of polymer-grafted nanoparticles (gNPs) in homopolymer matrices is investigated using coarse-grained simulations. Simulations are performed using theoretically informed Langevin dynamics (TILD), a particle-based method that uses a particle-to-mesh scheme to efficiently calculate the nonbonded interactions. Direct two-phase simulations are used to determine coexistence curves. The phase diagram for NPs densely grafted with short A chains and blended with long B homopolymer chains is significantly shifted compared to that for an AB homopolymer blend with chains of the same lengths. This is due to a loss of chain configurational entropy for the long B matrix chains to penetrate the polymer brushes around the gNPs. Adding additional A homopolymer to the polymer matrix leads to an increase in miscibility of the gNPs on the gNP-rich side of the phase diagram. The extra A homopolymer helps to compatibilize the interface between the gNPs and the matrix B chains. Our results are consistent with both experiments and modeling of poly(methyl methacrylate) (PMMA)-grafted silica NPs in poly(styrene-ran-acrylonititrile) (SAN) and PMMA-NP/SAN/PMMA composites.