Computational chemistry study on the interaction mechanism of imidazolium based ionic liquid lubricants with metal surface
- Ugur Mart
Ionic liquids (ILs) constitute a new class of substances that possess unique characteristics which make them ideal candidates for high performance task-specific lubricants even under severe conditions such as high pressure and temperatures. The tribological performance of a lubricant is directly related with film formation capability on the substrate. The high polarity of ILs makes them able to form a strong and effective adsorption film that improve the tribological performance with tribochemical reactions. This mechanism is strongly dependent on the molecular structures of ILs. However, one of the key questions is still unclear that how ILs interact with substrates. Hence, the interaction mechanism and tribochemical reactions of ILs with the substrates need to be examined in order to ensure the formation of tribofilms on specific surfaces. We propose a fundamental research to investigate the interaction mechanism of ionic liquids (ILs) with metal surfaces, molecular structure and organization on the surface along with chemical reactions using computational chemistry methods at molecular level. Imidazolium based ILs have been used in this study due to their excellent properties of stability, flexibility in molecular design and adaptability to multiple functions. The interaction mechanism of imidazolium ILs with different alkyl chain length has been investigated. Quantum mechanics and molecular dynamics methods have been performed to simulate the tribochemical reactions and dynamical behaviour of the IL molecules on Fe surfaces. Potential parameters for molecular dynamic simulations were obtained from a series of sequential DFT/QCMD/MD calculation processes. The adsorption model explains the effect of alkyl chain length on the tribological properties of ILs that those with longer alkyl chains are more liable to form a densely packed molecular layer due to more enthalpy gain, so have better tribological properties.