Lithium Salt-Induced Microstructure and Ordering in Diblock Copolymer/Homopolymer Blends

This work details the phase behavior of a pseudoternary polymer blend system containing poly(ethylene oxide) (PEO) and polystyrene (PS) homopolymers, a PS-PEO block copolymer, and lithium bis(trifluoromethane)sulfonamide (LiTFSI). The phase behavior of the system is described along the volumetrically symmetric isopleth at a fixed LiTFSI concentration relative to the PEO component. The addition of LiTFSI dramatically increases the segregation strength of the blend, causing the otherwise globally disordered blends to exhibit a variety of microstructured morphologies typically found in salt-free ternary polymer blends, such as lamellae, a hexagonal phase, and a bicontinuous microemulsion. The breadth of morphologies and segregation strengths that can be accessed in this system by simply tuning blend composition establishes a new framework for the design of future ternary blend systems and, more broadly, polymeric materials where microstructured, well-segregated domains with tunable ion transport properties are desirable.