Insights from molecular dynamics simulations on structural organization and diffusive dynamics of an ionic liquid at...

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Accurate modeling of ionic liquids (ILs) is crucial for understanding their bulk and interfacial properties.
• Experimentally inaccessible properties, especially near interfaces, require reliable simulation methods.
• Ionic liquids exhibit unique behaviors influenced by their proximity to vacuum and solid surfaces.

Purpose of the Study:

• To develop and validate a robust computational approach for characterizing static and dynamic properties of ionic liquids.
• To investigate the influence of interfaces on ionic liquid behavior.
• To predict properties of confined ionic liquid films.

Main Methods:

• Molecular dynamics simulations of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2Mim][NTf2]) in bulk and film configurations.
• Evaluation of different charge models (CHelpG, RESP-HF, RESP-B3LYP) and scaling factors.
• Benchmarking simulation results against experimental data including self-diffusion coefficients, surface tension, and X-ray reflectivity.

Main Results:

• The RESP-HF/0.9 charge model with a scaling factor of 0.9 was identified as the optimal non-polarizable force field for [C2Mim][NTf2].
• Detailed characterization of ionic liquid molecular configurations and orientations relative to vacuum and sapphire interfaces.
• Analysis of density and in-plane/normal mobilities, revealing persistent correlations between stratification and transport up to several nanometers from interfaces.

Conclusions:

• The optimized force field enables accurate prediction of interfacial ionic liquid properties.
• Strong correlations between stratification and diffusive transport exist in confined ionic liquids.
• This modeling approach advances the understanding of ionic liquids in interfacial environments.