Irreversible structural change of a dry ionic liquid under nanoconfinement

L. Andres Jurado, Hojun Kim, Andrea Arcifa, Antonella Rossi, Cecilia Leal, Nicholas D. Spencer, Rosa M. Espinosa-Marzal

Research output: Contribution to journalArticlepeer-review

Abstract

Studies of 1-hexyl-3-methyl-imidazolium ethylsulfate ([HMIM] EtSO4) using an extended surface forces apparatus show, for the first time, an ordered structure within the nanoconfined ionic liquid (IL) between mica surfaces that extends up to ∼60 nm from the surface. Our measurements show the growth of this ordered IL-film upon successive nanoconfinements - the structural changes being irreversible upon removal of the confinement - and the response of the structure to shear. The compressibility of this system is lower than that typically measured for ILs, while creep takes place during shear, both findings supporting a long-range liquid-to-solid transition. AFM (sharp-tip) studies of [HMIM] EtSO4 on mica only reveal ∼2 surface IL-layers, with order extending only ∼3 nm from the surface, indicating that confinement is required for the long-range IL-solidification to occur. WAXS studies of the bulk IL show a more pronounced ordered structure than is the case for [HMIM] with bis(trifluoromethylsulfonyl)imide as anion, but no long-range order is detected, consistent with the results obtained with the sharp AFM tip. These are the first force measurements of nanoconfinement-induced long-range solidification of an IL.

Original languageEnglish (US)
Pages (from-to)13613-13624
Number of pages12
JournalPhysical Chemistry Chemical Physics
Volume17
Issue number20
DOIs
StatePublished - May 28 2015

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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