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Composition Dependence of the Flory–Huggins Interaction Parameters of Block Copolymer Electrolytes and the Isotaksis Point

Journal Article · · Macromolecules
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  1. Univ. of California, Berkeley, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Joint Center for Energy Storage Research
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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 (N$$f_{EO}$$)-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, $$f_{EO,salt,}$$ and salt concentration. At $$f_{EO,salt,}$$ > 0.27, the addition of salt stabilizes the ordered phase; at $$f_{EO,salt,}$$ < 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 ($$f_{EO,salt,}$$ = 0.27). Here, we refer to this composition as the “isotaksis point”.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Science Foundation (NSF)
Grant/Contract Number:
AC02-05CH11231; AC02-76SF00515
OSTI ID:
1605253
Journal Information:
Macromolecules, Journal Name: Macromolecules Journal Issue: 15 Vol. 52; ISSN 0024-9297
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English

Figures / Tables (13)

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY