(251h) Molecular Simulation of the Influence of Nanoparticles on the Bicontinuous Phases of Diblock Copolymer Melts

Martínez-Veracoechea, F., Cornell University
Escobedo, F. A., Cornell University

Molecular simulations of diblock copolymers were performed in both discrete space via a lattice Monte Carlo method and in continuum space via Dissipative Particle Dynamics. In addition to the classical morphologies formed by diblock copolymers, we are able to simulate and outline the phase boundaries of the bicontinuous Gyroid (G) phase. We find that the triply periodicity of the G phase makes it especially sensitive to finite size effects. By examining the structure of the G phase and its nodes (the junctions where channels formed by the minority component merge), we find evidence of packing frustration in the form of chain stretching inside such nodes. Because this packing frustration explains the limited viability of the G phase in the thermodynamic phase space, we also studied two ways of relieving such a frustration: the introduction of chain length bidispersity and the addition of selective nanoparticles. We find that chain length bidispersity can increase the range of temperatures where the G phase is stable. We also find that while ?small? selective nanoparticles can get integrated into a G phase for some range of concentration, they can also induce the formation of other complex mesophases. In particular, we observe the formation of a co-continuous phase (where the minority component forms a single regular network) not only in nanoparticle-containing systems but, surprisingly, also in the neat diblock copolymer system. Finally, we explore the effects of selective larger nanoparticles on the stability of different bicontinuous phases (e.g., Gyroid, Double Diamond, and Plumber's Nightmare) and outline a tentative phase diagram for a nanoparticle-diblock copolymer binary system.