Formation of a C15 laves phase with a giant unit cell in salt-doped A/B/Ab ternary polymer blends

Timothy P. Lodge; Shuyi Xie; Aaron P. Lindsay; Frank S. Bates

doi:10.1021/acsnano.0c06071

Formation of a C15 laves phase with a giant unit cell in salt-doped A/B/Ab ternary polymer blends

Timothy P. Lodge, Shuyi Xie, Aaron P. Lindsay, Frank S. Bates

Research output: Contribution to journal › Article › peer-review

21 Scopus citations

Abstract

Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), ¹H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕ_H = 0.8 with a salt composition r = 0.06 (Li⁺/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (f_core = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕ_PEO,homo-_LiTFSI/ϕ_H = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.

Original language	English (US)
Pages (from-to)	13754-13764
Number of pages	11
Journal	ACS nano
Volume	14
Issue number	10
DOIs	https://doi.org/10.1021/acsnano.0c06071
State	Published - Oct 27 2020

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. S.X. acknowledges partial funding from a Doctoral Dissertation Fellowship at the University of Minnesota and A.P.L. acknowledges a National Science Foundation Graduate Research Fellowship under grant no. 00039202. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at 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. Helpful discussion with Andreas J. Mueller on the electron density map reconstruction is appreciated.

Publisher Copyright:
© 2020 American Chemical Society

Keywords

Block copolymer
C15 Laves phase
Electrolyte
Homopolymer
Salt doping
Self-assembly
Ternary blend

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abstract = "Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), 1H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕH = 0.8 with a salt composition r = 0.06 (Li+/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (fcore = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕPEO,homo-LiTFSI/ϕH = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.",

keywords = "Block copolymer, C15 Laves phase, Electrolyte, Homopolymer, Salt doping, Self-assembly, Ternary blend",

author = "Lodge, {Timothy P.} and Shuyi Xie and Lindsay, {Aaron P.} and Bates, {Frank S.}",

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. S.X. acknowledges partial funding from a Doctoral Dissertation Fellowship at the University of Minnesota and A.P.L. acknowledges a National Science Foundation Graduate Research Fellowship under grant no. 00039202. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at 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. Helpful discussion with Andreas J. Mueller on the electron density map reconstruction is appreciated. Publisher Copyright: {\textcopyright} 2020 American Chemical Society",

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T1 - Formation of a C15 laves phase with a giant unit cell in salt-doped A/B/Ab ternary polymer blends

AU - Lodge, Timothy P.

AU - Xie, Shuyi

AU - Lindsay, Aaron P.

AU - Bates, Frank S.

N1 - 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. S.X. acknowledges partial funding from a Doctoral Dissertation Fellowship at the University of Minnesota and A.P.L. acknowledges a National Science Foundation Graduate Research Fellowship under grant no. 00039202. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at 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. Helpful discussion with Andreas J. Mueller on the electron density map reconstruction is appreciated. Publisher Copyright: © 2020 American Chemical Society

PY - 2020/10/27

Y1 - 2020/10/27

N2 - Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), 1H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕH = 0.8 with a salt composition r = 0.06 (Li+/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (fcore = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕPEO,homo-LiTFSI/ϕH = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.

AB - Salt-doped A/B/AB ternary polymer blends, wherein an AB copolymer acts as a surfactant to stabilize otherwise incompatible A and B homopolymers, display a wide range of nanostructured morphologies with significant tunability. Among these structures, a bicontinuous microemulsion (BμE) has been a notable target. Here, we report the surprising appearance of a robust C15 Laves phase, at compositions near where the BμE has recently been reported, in lithium bis(trifluoromethane) sulfonimide (LiTFSI)-doped low-molar-mass poly(ethylene oxide) (PEO)/polystyrene (PS)/symmetric PS-b-PEO block copolymer blends. The materials were analyzed by a combination of small-angle X-ray scattering (SAXS), 1H NMR spectroscopy, and impedance spectroscopy. The C15 phase emerges at a high total homopolymer volume fraction ϕH = 0.8 with a salt composition r = 0.06 (Li+/[EO]) and persists as a coexisting phase across a large area of the isothermal phase diagram with high PS homopolymer compositions. Notably, the structure exhibits a huge unit cell size, a = 121 nm, with an unusually high micelle core volume fraction (fcore = 0.41) and an unusually low fraction of amphiphile (20%). This unit cell dimension is at least 50% larger than any previously reported C15 phase in soft matter, despite the low molar masses used, unlocking the possibility of copolymer-based photonic crystals without compromising processability. The nanostructured phase evolution from lamellar to hexagonal to C15 along the EO60 isopleth (ϕPEO,homo-LiTFSI/ϕH = 0.6) is rationalized as a consequence of asymmetry in the homopolymer solubility limit for each block, which leads to exclusion of PS homopolymer from the PS-b-PEO brush prior to exclusion of the PEO homopolymer, driving increased interfacial curvature and favoring the emergence of the C15 Laves phase.

KW - Block copolymer

KW - C15 Laves phase

KW - Electrolyte

KW - Homopolymer

KW - Salt doping

KW - Self-assembly

KW - Ternary blend

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Formation of a C15 laves phase with a giant unit cell in salt-doped A/B/Ab ternary polymer blends

Abstract

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