Nanostructured materials with co-continuous structures, in which each discrete domain is independently interconnected, can simultaneously achieve orthogonal properties such as rapid ion transport and excellent mechanical strength. Potential applications include porous membranes, fuel cells, and rechargeable metal batteries. A promising route involves blending an A–B diblock copolymer with the constituent A and B homopolymers, leading to a disordered bicontinuous microemulsion (BuE) state. We have shown that charge-free ternary A–B/A/B polymer blends universally self-assemble into the thermodynamically stable BuE phase, albeit with carefully designed molecular weights and compositions. The BuE is found in a narrow window near the location of an isotropic Lifshitz point predicted by mean-field theory, and is presumably stabilized by fluctuations. The interesting question that arises is whether this phase can also be accessed in blends containing charge, where in general the intermolecular interactions are stronger and more long-ranged. We are exploring this issue in two systems: an A–B/A/B ternary system with added salt, and an A–B/A/B system in which one of the polymers is ionomeric. Surprisingly, in both cases an even wider BuE channel occurs for symmetric compositions (equal volumes of A and B), despite huge asymmetries in the binary blend phase diagram for the same system. Furthermore, the ion transport properties of these materials are quite promising.

Bicontinuous structures in charged polymer blends

ACS Fall 2020 Virtual Meeting

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