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 °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 φH = φPS,homo + φPEO,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.
Bibliographical noteFunding Information:
This work was supported by the Office of Basic Energy Sciences (BES) of the U.S. Department of Energy (DOE) under contract no. DE-FOA-0001664. S.X. acknowledges partial funding from a Doctoral Dissertation Fellowship at the University of Minnesota. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located in the Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by E.I. DuPont de Nemours & Co., the Dow Chemical Company, and Northwestern University. Use of the APS, an Office of Science User Facility operated for the U.S. DOE Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under contract no. DE-AC02-06CH11357. The authors acknowledge the support of the National Institute of Standards and Technology and the U.S. Department of Commerce in providing the neutron research facilities used in this work and thank our local contact Dr. Yimin Mao for help with the SANS experiments.
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