Fluctuation effects in A + B + AB ternary polymer blends

Adding copolymers to homopolymer blends enhances their compatibility and, at higher copolymer concentrations, leads to the formation of microemulsions. Contrary to what is seen in mean-field theory, experiments find that the disordered phase invades the ordered region of the phase diagram, introducing a channel of microemulsions. The channel separates the two-phase region, on the homopoylmer-rich side, from the lamellar region, on the copolymer-rich side. This modification to the phase behavior is due to fluctuations, and understanding it requires simulations that go beyond mean-field theory. We build on existing simulation techniques, extending Monte Carlo field-theoretic simulations of ternary blends into three dimensions, and introducing new semi-grand canonical ensembles, in order to tackle the problems of phase behavior, interfacial properties and the nature of microemulsions. This work examines A and B homopolymers with the experimentally relevant invariant polymerization index of Ñ = 10⁴, blended with symmetric AB diblock copolymers of lengths α=2.5, 5 and 10 times longer than the homopolymers.