Structure and Properties of Bicontinuous Microemulsions from Salt-Doped Ternary Polymer Blends

Shuyi Xie, Daniel J. Meyer, En Wang, Frank S. Bates, Timothy P. Lodge

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20 Scopus citations

Abstract

We have systematically examined the phase behavior of lithium salt-doped A/B/AB ternary polymer blends composed of low-molar-mass poly(ethylene oxide) (PEO) and polystyrene (PS) homopolymers, a symmetric PS-b-PEO block copolymer (SO), and lithium bis(trifluoromethane) sulfonimide (LiTFSI) by a combination of small-angle neutron scattering and small-angle X-ray scattering, bolstered by ionic conductivity measurements. The salt partitions exclusively to the PEO and acts to increase the segregation strength of the blends, leading either to macroscopic or microscopic phase segregation. By constraining the volume fractions of the two homopolymers to be the same (φPEO+LiTFSIPS = 1), a two-dimensional phase diagram along the volumetrically symmetric isopleth of the phase prism has been mapped out, and a well-structured bicontinuous microemulsion (BμE) is found over a wider range of total homopolymer composition (ca. φH ≈ 80-86%), compared to the neutral polymer case, where a 1-3% range in φH is typical. The characteristics of the BμE are obtained via the Teubner-Strey structure factor and are tunable by φH, temperature, and salt concentration. Moreover, the BμE possesses superior ionic transport properties, demonstrating higher conductivity compared to both microphase-separated (lamellar) and nonstructured disordered blends. This work offers a strategy to obtain well-defined microstructured ion-containing polymer systems with tunable co-continuous morphology and favorable conductivity properties, which could help optimize the design of polymer electrolytes.

Original languageEnglish (US)
Pages (from-to)9693-9702
Number of pages10
JournalMacromolecules
Volume52
Issue number24
DOIs
StatePublished - Dec 24 2019

Bibliographical note

Funding 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. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). We 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 Yimin Mao for the help in setting up the SANS experiments. Some experiments were conducted in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program, Award DMR-1420013. S.X. acknowledges some funding from a Doctoral Dissertation Fellowship at the University of Minnesota, and we thank Hongyun Xu and Bo Zhang for helpful discussions.

Funding 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. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). We 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 Yimin Mao for the help in setting up the SANS experiments. Some experiments were conducted in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program, Award DMR-1420013. S.X. acknowledges some funding from a Doctoral Dissertation Fellowship at the University of Minnesota, and we thank Hongyun Xu and Bo Zhang for helpful discussions.

Publisher Copyright:
© 2019 American Chemical Society.

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