Investigating the Effect of Added Salt on the Chain Dimensions of Poly(Ethylene Oxide) through Small-Angle Neutron Scattering

Published

November 26, 2019

Author(s)

Whitney Loo, Katrina I. Mongcopa, Daniel A. Gribble, Antonio Faraone, Nitash P. Balsara

Abstract

We have measured the effect of added salt on the chain dimensions of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) in the melt state through small angle neutron scattering experiments. Scattering profiles from blends of hydrogenated and deuterated PEO mixed with LiTFSI were measured as a function of salt concentration. Scattering profiles from pure deuterated PEO/LiTFSI mixtures were used for background subtraction purposes. The densities of PEO/LiTFSI mixtures of varying salt concentrations were measured to calculate partial molar monomer volumes of PEO and LiTFSI to account for non-ideal mixing, which turned out to be negligible. Kratky plots of the scattering profiles were used to calculate the salt concentration dependence of statistical segment length. At low salt concentrations, segment length decreases with increasing salt concentration, before increasing with increasing salt concentration in the high salt concentration regime. The Random Phase Approximation was used to predict theoretical scattering profiles from the calculated segment lengths; there is excellent agreement between the theoretical and measured scattering profiles at all salt concentrations. The scattering profiles of the pure deuterated PEO/LiTFSI mixtures showed ion clusters of characteristic size of 0.51 nm at high salt concentrations. The presence of ion clusters is hypothesized to cause the increase in segment length seen in this salt concentration window. The electrochemical performance of PEO/LiTFSI mixtures undoubtedly depends on chain conformation. The changes in statistical segment length with salt concentration mirror the dependence of some of the electrochemical properties of these systems on salt concentration.

Citation

Macromolecules

Volume

52

Issue

22

Pub Type

Journals

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Citation

Loo, W. , Mongcopa, K. , Gribble, D. , Faraone, A. and Balsara, N. (2019), Investigating the Effect of Added Salt on the Chain Dimensions of Poly(Ethylene Oxide) through Small-Angle Neutron Scattering, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=928510 (Accessed December 12, 2024)