Phase behavior of partially charged polymer ternary blends*

Single-ion-conducting block copolymers are of great interest due to their potential as solid electrolytes in, e.g., lithium-ion batteries. However, delicate control of polymer composition to optimize the structure-conductivity compromise remains a challenge. Alternatively, blending a block copolymer (A-B) with homopolymers (A/B) offers an easy way to tune the microstructure by just varying the volume ratio of each polymer component. Despite numerous studies on neutral polymer systems, the phase behavior of partially charged ternary blends has not been thoroughly investigated. In this work, we examine the phase behavior of three ternary systems composed of poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)] (POEGMA), polystyrene (PS) and the corresponding block copolymer (POEGMA -PS), with different charge fractions. Small-angle X-ray scattering was used as the primary technique to map out the three-component phase prisms, where large windows of phase coexistence were observed. Additionally, these phase diagrams were found to deviate from symmetry due to the combined effect of charge and conformational asymmetry.