Role of blend asymmetries on the thermodynamics of highly confined polymer nanocomposites

Infiltration of polymer blends into the interstices of dense nanoparticle (NP) packings leads to the formation of highly loaded nanocomposites with unique mechanical and transport properties. Polymers in such nanocomposites are subjected to extreme physical confinement which alters the thermodynamics of the blend, increasing miscibility over their bulk counterparts. Additionally, these polymers are exposed to a very large nanoparticle surface area, increasing the impact of polymer-NP interactions on equilibrium behavior, particularly when one polymer in the blend has a stronger affinity for the NP surfaces. Here we present a computational study using field theoretic simulations to investigate the impact of polymer-nanoparticle interactions on the phase separation dynamics and equilibrium structure of polymer blend nanocomposites. We find that asymmetric polymer-NP interactions increase the window of miscibility of polymer blends, working in tandem with physical confinement to further increase the critical point. In the limit of very strong surface interactions, we observe a transition to pore-scale phase separation with one polymer phase wetting the nanoparticle surfaces. In addition, we introduce asymmetry in chain length and stiffness to explore diverse composite structures with potential for experimental development.