Nanoparticle additives provide a means of imparting the desired electrical, optical, or mechanical properties to a polymeric matrix. The difficulty faced in creating these composites is determining the optimal conditions for forming a thermodynamically stable mixture, where the particles will not phase separate from the matrix material. This challenge is even more daunting when the polymeric matrix is itself a multicomponent mixture, as is often the case in advanced materials. Ideally, the nanoparticles would not only contribute the needed physical properties, but also stabilize the mixture so that the entire system forms a single-phase system. In this study, we use a free energy expression for a binary blend that contains nanoparticles and take the interaction parameters between the different species to be independent variables. Thus, the particles can have distinct enthalpic interactions with each of the polymeric components. Using this expression, we determine the conditions under which the mixture forms a stable, single-phase material. In particular, we isolate how variations in the system's parameters (e.g., polymer composition, particle volume fraction, particle size, interaction energies) affect the phase diagrams. The findings provide guidelines for creating effective formulations and can allow researchers to understand how choices made in the nature of the components affect the overall macroscopic properties. (c) 2006 Wiley Peiiodicals, Inc.