Irreversible structural change of a dry ionic liquid under nanoconfinement
L Andres Jurado1, Hojun Kim, Andrea Arcifa
1Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, IL-61801 Urbana, USA. rosae@illinois.edu.
Physical Chemistry Chemical Physics : PCCP
|May 6, 2015
Summary
Nanoconfinement induces a long-range liquid-to-solid transition in ionic liquids. This study reveals an ordered ionic liquid film up to 60 nm thick between mica surfaces, demonstrating irreversible structural changes under confinement.
Area of Science:
- Materials Science
- Physical Chemistry
- Surface Science
Background:
- Ionic liquids (ILs) exhibit unique properties due to their ionic nature.
- Understanding IL behavior under confinement is crucial for applications in nanotechnology and lubrication.
- Previous studies lacked detailed insights into IL structural ordering at the nanoscale under confinement.
Purpose of the Study:
- To investigate the structural ordering and phase transitions of ionic liquids under nanoconfinement.
- To explore the influence of confinement geometry on IL film properties.
- To characterize the mechanical response of confined ILs to shear forces.
Main Methods:
- Extended Surface Forces Apparatus (SFA) to measure forces and structure of ILs between mica surfaces.
- Atomic Force Microscopy (AFM) with sharp tips to probe surface layers.
- Wide-Angle X-ray Scattering (WAXS) to analyze bulk IL structure.
Main Results:
- Observed an ordered ionic liquid ([HMIM] EtSO4) film extending up to ~60 nm under nanoconfinement.
- Demonstrated irreversible structural changes in the IL film upon confinement and de-confinement.
- Measured lower compressibility and observed shear creep, indicating a liquid-to-solid transition.
- AFM and WAXS studies showed limited surface ordering (~3 nm) and no long-range order in bulk IL, highlighting the necessity of confinement.
Conclusions:
- Nanoconfinement is essential for inducing long-range solidification in ionic liquids.
- The observed phenomenon represents the first force measurements of nanoconfinement-induced IL solidification.
- Findings suggest potential for designing IL-based materials with tunable solid-like properties under specific confinement conditions.
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