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Surface-Induced Ordering Depresses Through-Film Ionic Conductivity in Lamellar Block Copolymer Electrolytes
journal contribution
posted on 2020-03-27, 16:23 authored by Jonathan P. Coote, Thomas Kinsey, Dayton P. Street, S. Michael Kilbey, Joshua R. Sangoro, Gila E. SteinLamellar
block copolymers based on polymeric ionic liquids (PILs) show promise
as electrolytes in electrochemical devices. However, these systems
often display structural anisotropy that depresses the through-film
ionic conductivity. This work hypothesizes that structural anisotropy
is a consequence of surface-induced ordering, where preferential adsorption
of one block at the electrode drives a short-range stacking of the
lamellae. This point was examined with lamellar diblock copolymers
of polystyrene (PS) and poly(1-(2-acryloyloxyethyl)-3-butylimidazolium
bis(trifluoromethanesulfonyl)imide) (PIL). The bulk PS–PIL
structure was comprised of randomly oriented lamellar grains. However,
in thin PS–PIL films (100–400 nm), the lamellae were
stacked normal to the plane of the film, and islands/holes were observed
when the as-prepared film thickness was incommensurate with the natural
lamellar periodicity. Both of these attributes are well-known consequences
of preferential wetting at surfaces. The ionic conductivity of thick
PS–PIL films (50–100 μm) was approximately 20×
higher in the in-plane direction than in the through-plane direction,
consistent with a mixed structure comprised of randomly oriented lamellae
throughout the interior of the film and highly oriented lamellae at
the electrode surface. Therefore, to fully optimize the performance
of a block copolymer electrolyte, it is important to consider the
effects of surface interactions on the ordering of domains.
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electrode drivesPILanisotropyshow promisethrough-plane directionlamellar diblock copolymersconductivityPSsurface interactionselectrode surfacein-plane directionconsequenceas-prepared film thicknessSurface-Induced Ordering Depresses Through-Filmblock copolymer electrolyteLamellar Block Copolymer Electrolytes Lamellar block copolymerswork hypothesizeslamellaelamellar periodicitylamellar grainselectrochemical devices
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