Phase Behavior of Salt-Doped A/B/AB Ternary Polymer Blends: The Role of Homopolymer Distribution

Salt-doped A/B/AB ternary polymer blends demonstrate a plethora of nanostructured morphologies tunable by the composition of homopolymers (A and B) and the corresponding diblock copolymer (AB). Here, we report a complete phase diagram of lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass polystyrene (PS)/poly(ethylene oxide) (PEO)/symmetric PS-b-PEO block copolymer (SO) blends and evaluate the spatial distribution of homopolymers in the resulting microstructures. In the isothermal phase triangle at 120 degrees C and r = [Li+]/[EO] = 0.06, a wide region of lamellae (LAM) is bracketed by small zones of double gyroid (GYR) and wide regions of hexagonally packed cylinders (HEX); adjacent to HEX is a significant region of the C15 Laves phase. At a high total homopolymer composition phi(H) = phi(PS,homo) + phi(PEO,homo+LiTFSI), the copolymer brush becomes saturated and begins to exclude homopolymers, resulting in a rapid domain size increase and inducing the formation of higher curvature phases, as suggested by small-angle X-ray scattering (SAXS). This phenomenon is distinct from charge-neutral ternary blends. Moreover, small-angle neutron scattering (SANS) profiles of selectively deuterated lamellar and bicontinuous ternary blends with contrast variation confirm the existence of a pure PS homopolymer layer in the middle of the PS microdomain.

Automated summary

Salt-doped A/B/AB ternary polymer blends exhibit a variety of nanostructured morphologies that can be tuned by the composition of homopolymers and diblock copolymers. Studies on phase diagrams of lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped polymer blends show that the composition of homopolymers can affect the resulting microstructures, leading to the formation of higher curvature phases under certain conditions.