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Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy
Published on: May 27, 2018
Nonlinear vibrational spectroscopic studies on waterlionic liquid([C(n)mim]TFSA: n = 4, 8) interfaces
Takashi Iwahashi1, Yasunari Sakai, Doseok Kim
1Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, 464-8602, Japan.
Investigating water interfaces with room temperature ionic liquids (RTILs) using spectroscopy and simulation reveals distinct interactions. Hydrogen bonding between [TFSA]- anions and water molecules at the interface causes specific spectral shifts.
Area of Science:
- Physical Chemistry
- Surface Science
- Materials Science
Background:
- Room temperature ionic liquids (RTILs) are tunable solvents with unique interfacial properties.
- Understanding the molecular structure of liquid interfaces is crucial for various applications.
- The interaction between water and ionic liquid interfaces requires detailed investigation.
Purpose of the Study:
- To elucidate the molecular structure and interactions at water/RTIL interfaces.
- To compare interfacial properties between air/RTIL and water/RTIL systems.
- To investigate the role of [TFSA]- anions and [C(n)mim]+ cations in interfacial organization.
Main Methods:
- Infrared-visible sum frequency generation (IV-SFG) vibrational spectroscopy was employed.
- Molecular dynamics (MD) simulations were conducted for detailed analysis.
- SFG spectra were analyzed in the SO stretch region.
Main Results:
- SFG spectra at the water/RTIL interface showed significant differences compared to the air/RTIL interface.
- A broadened and blue-shifted SO2-ss mode peak was observed at the water/RTIL interface.
- MD simulations confirmed preferential orientation of SO2 groups of [TFSA]- anions towards the water phase.
- The ordering of [C(n)mim]+ alkyl chains influenced the polar orientation of [TFSA]- anions.
Conclusions:
- Hydrogen bonding between [TFSA]- anions and water molecules leads to inhomogeneous intermolecular interactions at the interface.
- The observed spectral features are consistent with the preferential orientation of anions towards water.
- The structure of cations plays a role in organizing the interfacial layer.
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