Thermodynamic behavior of particle/diblock copolymer mixtures: Simulation and theory

We investigate the influence of hard nanoparticles on the phase behavior of diblock copolymers. Using Monte Carlo simulations, we obtain phase diagrams as a function of the nanoparticle size and concentration. When the size of the nanoparticles becomes comparable to the radius of gyration of the minority (A) block, we observe the formation of new superstructures, where the particles self-assemble inside the copolymer micelles. We develop a theoretical model, based on the strong segregation limit approximation, and show that these self-assembled structures can be either stable or metastable, depending on the particle size and volume fraction. The formation of such phases is due to the interplay between the particle-particle excluded-volume interactions, preferential particle/block-A interactions, and the enthalpic and stretching interactions within the diblock.