Morphology and ion transport in ion-containing block copolymers

Ion-containing block copolymers, where one of the microdomains has charged species, have attracted considerable attention for solid-state polymer electrolytes because they provide advantageous combinations of transport and mechanical properties. Block copolymers also provide a unique opportunity to control the nanoscale, self-assembled morphology and this morphology strongly impacts the transport and mechanical properties. Thus, understanding the morphology is critical to developing precise correlations between the molecular structure, morphology, and transport properties of ion-containing block copolymers. In this thesis, a variety of morphologies in diblock copolymers incorporating ionic liquids (ILs) and sulfonated styrenic pentablock copolymers have been investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The incompatibility between ionic and non-ionic blocks in both IL-doped and polymerized ionic liquid (PIL) diblock copolymers can produce strong microphase separation, and a variety of morphology types including cylindrical, lamellar, and coexisting lamellae and network morphologies are observed. The formation of these periodic nanostructures is hampered by the presence of partial miscibility between blocks in PIL block copolymers. The incorporation with sulfonic acid group into pentablock copolymers also leads to microphase separation without long-range order. Morphologies in these ion-containing block copolymers are very sensitive to processing conditions and can be trapped in non-equilibrium morphologies due to the strong interactions between ionic and non-ionic blocks. The microphase separation into ionic and non-ionic microdomains improves ionic conductivity due to the enhanced local ion concentration in the conductive microdomains. Improved ionic conductivity is even observed in weakly microphase separated systems. We also found that the glass transition temperature, dimensionality, and orientation of the conducting microdomains are key factors in determining ionic conductivity in IL-incorporated diblock copolymers. The continuity of the conductive microdomains also strongly impacts water transport properties in sulfonated pentablock copolymers. Further investigations of ion conduction in PIL homopolymer thin films elucidate the importance of interfacial regions in ion conduction when polymer chains are confined in nanometric length scale. These findings extend our understanding of the relationships between morphology and ion transport properties in ion-containing block copolymers