Ion Diffusion Reveals Heterogeneous Viscosity in Nanostructured Ionic Liquids

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Ionic liquids (ILs) often exhibit nanostructured domains with differing physical properties.
• Bulk parameters like viscosity may not accurately represent the behavior of these distinct nanoscale networks.
• Understanding local environments is crucial for mass and charge transport in ILs.

Purpose of the Study:

• To address the limitations of bulk property descriptions in nanostructured ionic liquids.
• To apply the Saffman-Delbrück model to interpret ion self-diffusion.
• To experimentally probe the relative viscosities of polar and apolar networks in ILs.

Main Methods:

• Utilizing pulsed field gradient NMR spectroscopy to measure ion self-diffusion coefficients.
• Analyzing data using the Saffman-Delbrück model for nanostructured media.
• Investigating the homologous series of [C_nmim][NTf₂] ionic liquids.

Main Results:

• Demonstrated the capability of pulsed field gradient NMR to differentiate network viscosities.
• Calculated polar network viscosities that align well with existing simulation data.
• Provided experimental evidence for the distinct viscoelastic properties of nanoscale networks in ILs.

Conclusions:

• Pulsed field gradient NMR spectroscopy offers a powerful tool for characterizing local environments in ILs.
• The findings enhance the understanding of mass and charge transport mechanisms in nanostructured ionic liquids.
• This experimental approach can be broadly applied to study other structured fluids.