Final Report: Grant DE-FG02-05ER15682. Simulation of Complex Microphase Formation in Pure and Nanoparticle-filled Diblock Copolymers

Abstract

The goal of this project was to use molecular simulation to quantify the impact of additives on the onset and structure of bicontinuous phases in linear diblock copolymers (DBC). The focus was on understanding how additives with selective affinity for a given block will distribute and perturb the structure of complex bicontinuous phases (like gyroid, double diamond, and plumbers nightmare whose minority component block forms two interweaving 3D networks) in DBCs; it was hypothesized that a suitable choice of additive type, size, affinity, and concentration may suppress or stabilize a particular bicontinuous phase. The ultimate goal in this line of investigation is to elucidate the rational design of the optimal additive for which the composition range of stability of a particular bicontinuous phase is maximized. Ours are the first published simulation studies to report on the formation of the gyroid phase in DBC melts and of other bicontinuous phases in DBC-modified by homopolymer. The following tasks were carried out: (i) simulation of bicontinuous phases of pure DBCs via both on-lattice Monte Carlo simulations and continuum-space Monte Carlo and molecular dynamics simulations, (ii) determination of the effect of selective additives (homopolymer) of different sizes on such bicontinuous phases, and (iii) development of novel Monte Carlo methods to map out reliable phase diagrams and improve ergodic sampling; in particular, optimized expanded-ensemble techniques for measuring free-energies and for chemical potential equilibration.