Temperature-dependent structure of ionic liquids: X-ray scattering and simulations

Hemant K. Kashyap, Cherry S. Santos, Harsha V.R. Annapureddy, N. Sanjeeva Murthy, Claudio J. Margulis, Edward W. Castner

Research output: Contribution to journalArticlepeer-review

137 Citations (Scopus)


In this article we determine the temperature-dependent structure of the tetradecyltrihexylphosphonium bis(trifluoromethylsulfonyl)amide ionic liquid using a combination of X-ray scattering and molecular dynamics simulations. As in many other room-temperature ionic liquids three characteristic intermolecular peaks can be detected in the structure function S(q). A prepeak or first sharp diffraction peak is observed at about q = 0.42 Å -1. Long range anion-anion correlations are the most important contributors to this peak. In all systems we have studied to date, this prepeak is a signature of solvation asymmetry. The peak in S(q) near q = 0.75 Å -1 is the signature of ionic alternation and arises from the charge ordered separation of ions of the same charge. The most intense diffraction peak near q = 1.37 Å -1 arises from short-range separation between ions of opposite charge combined with a significant contribution from cationic carbon-carbon interactions, indicating that cationic hydrophobic tails have significant contacts.

Original languageEnglish
Pages (from-to)133-143
Number of pages11
JournalFaraday Discussions
Publication statusPublished - 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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