Interactions and Ordering of Ionic Liquids at a Metal Surface

Area of Science:

• Materials Science
• Computational Chemistry
• Surface Science

Background:

• Ionic liquids are advanced lubricants with tunable properties.
• Understanding ionic liquid-metal interactions is crucial for tribology.
• Developing accurate computational models for these systems is challenging.

Purpose of the Study:

• To develop an atomistic force field for ionic liquids interacting with metal surfaces.
• To enable accurate computer simulations of heterogeneous systems involving ionic liquids and metals.
• To investigate the structure and behavior of ionic liquids at the metal-liquid interface for tribological applications.

Main Methods:

• Quantum mechanical calculations (Density Functional Theory with M06 functional) were used to model ion-metal interactions.
• A site-site potential function was derived from DFT interaction energies, incorporating BSSE correction.
• Metal polarization effects were included using induced dipoles.
• Molecular dynamics simulations were performed using the developed force field.

Main Results:

• An accurate atomistic force field for ionic liquids on metal surfaces was successfully developed.
• Molecular dynamics simulations revealed the structure of the interfacial layer, including ion ordering and charge density profiles.
• The interfacial layer was typically one ion thick, with specific orientations of alkyl chains based on ion type and chain length.
• Oxygen atoms in sulfonyl groups showed strong interaction with the iron surface.

Conclusions:

• The developed force field accurately models ionic liquid-metal interactions.
• The study provides insights into the interfacial structure crucial for designing ionic lubricants.
• The model facilitates the simulation of tribological systems involving ionic liquids and metal surfaces or nanoparticles.