Composition dependence of the flory-huggins interaction parameters of block copolymer electrolytes and the isotaksis point

Whitney S. Loo, Gurmukh K. Sethi, Alexander A. Teran, Michael D. Galluzzo, Jacqueline A. Maslyn, Hee Jeung Oh, Katrina I. Mongcopa, Nitash P. Balsara

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Abstract

The thermodynamics of block copolymer/salt mixtures were quantified through the application of Leibler's random phase approximation to disordered small-Angle X-ray scattering profiles. The experimental system is comprised of polystyrene-block-poly(ethylene oxide) (SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI), SEO/LiTFSI. The Flory-Huggins interaction parameter determined from scattering experiments, χSC, was found to be a function of block copolymer composition, chain length, and temperature for both salt-free and salty systems. In the absence of salt, χ0,SC is a linear function of (NfEO)-1 in the presence of salt, a linear approximation is used to describe the effect of salt on χeff,SC for a given copolymer composition and chain length. The theory of Sanchez was used to determine χeff from χeff,SC to predict the boundary between order and disorder as a function of chain length, block copolymer composition, salt concentration, and temperature. At fixed temperature (100 °C), Ncrit, the chain length of SEO at the order-disorder transition in SEO/LiTFSI mixtures, was predicted as a function of the volume fraction of the salt-containing poly(ethylene oxide)-rich microphase, fEO,salt, and salt concentration. At fEO,salt > 0.27, the addition of salt stabilizes the ordered phase; at fEO,salt < 0.27, the addition of salt stabilizes the disordered phase. We propose a simple theoretical model to predict the block copolymer composition at which phase behavior is independent of salt concentration (fEO,salt = 0.27). We refer to this composition as the "isotaksis point". ©

Original languageEnglish (US)
Pages (from-to)5590-5601
Number of pages12
JournalMacromolecules
Volume52
Issue number15
DOIs
StatePublished - Aug 13 2019

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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    Loo, W. S., Sethi, G. K., Teran, A. A., Galluzzo, M. D., Maslyn, J. A., Oh, H. J., Mongcopa, K. I., & Balsara, N. P. (2019). Composition dependence of the flory-huggins interaction parameters of block copolymer electrolytes and the isotaksis point. Macromolecules, 52(15), 5590-5601. https://doi.org/10.1021/acs.macromol.9b00884