Effects of Electrolytes on Thermodynamics and Structure of Oligo(ethylene oxide)/Salt Solutions and Liquid-Liquid Equilibria of a Squalane/Tetraethylene Glycol Dimethyl Ether Blend

Zhengyuan Shen, Qile P. Chen, Shuyi Xie, Timothy P. Lodge, J. Ilja Siepmann

Research output: Contribution to journalArticlepeer-review

Abstract

Gibbs ensemble Monte Carlo simulations for salt-doped oligo(ethylene oxide) (OEO, Mw = 90-266 g/mol) solutions show that the presence of ions leads to significant increases in the cohesive energy density (Î CED) and the enthalpy of vaporization for OEO chains but that compensation by entropic contributions leads to only small changes in the Gibbs free energy of transfer and vapor pressure. At the same relative ion concentration (r) and temperature, the Î CED values of the salt-doped systems order as LiClO4 > LiF > CsClO4 ≈ CsF. Structural analysis indicates significant ion clustering in addition to coordination of cations by OEO chains. After accounting for ion clustering via the van't Hoff factor, the solvent vapor pressures are well described by Raoult's law. Experiments and simulations for a squalane/tetraethylene glycol dimethyl ether blend (xW,OEO = 0.65) show that the addition of LiClO4 does not significantly alter the miscibility gap below 0.95 TCP,free, the critical temperature of the salt-free blend. However, the coexistence curve for the LiClO4-doped system does not close with the usual power-law scaling at T > 0.95 TCP,free as transfer of OEO chains to the squalane-rich phase leads to an increase in r in the OEO-rich phase, which, in turn, makes it a less hospitable environment for squalane.

Original languageEnglish (US)
Pages (from-to)1120-1136
Number of pages17
JournalMacromolecules
Volume54
Issue number3
DOIs
StatePublished - Dec 18 2020

Bibliographical note

Funding Information:
This work was primarily supported by the National Science Foundation through the University of Minnesota MRSEC under Award DMR-2011401. Computer resources were provided by this NSF award and by the Minnesota Supercomputing Institute.

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