Odd-Even Structural Sensitivity on Dynamics in Network-Forming Ionic Liquids

Ke Yang, Zhikun Cai, Madhusudan Tyagi, Mikhail Feygenson, Joerg C. Neuefeind, Jeffrey S. Moore, Yang Zhang

Research output: Contribution to journalArticlepeer-review

Abstract

As a compelling case of sensitive structure-property relationship, an odd-even effect refers to the alternating trend of physical or chemical properties on odd/even number of repeating structural units. In crystalline or semicrystalline materials, such odd-even effects emerge as manifestations of differences in the periodic packing patterns of molecules. Therefore, due to the lack of long-range order, such an odd-even phenomenon is not expected for dynamic properties in amorphous state. Herein, we report the discovery of a remarkable odd-even effect of dynamical properties in the liquid phase. In a class of glass-forming diammonium citrate ionic liquids, using incoherent quasi-elastic neutron scattering measurements, we measured the dynamical properties including diffusion coefficient and rotational relaxation time. These directly measured molecular dynamics showed pronounced alternating trends with increased number of methylene (-CH2-) groups in the backbone. Meanwhile, the structure factor S(Q) showed no long-range periodic packing of molecules, while the pair distribution function G(r) revealed subtle differences in the local molecular morphology. The observed dynamical odd-even phenomenon in liquids showed that profound dynamical changes originate from subtle local structural differences.

Original languageEnglish (US)
Pages (from-to)3227-3233
Number of pages7
JournalChemistry of Materials
Volume28
Issue number9
DOIs
StatePublished - May 10 2016

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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