Ionic Liquids (ILs) are a rapidly growing class of materials with a broad spectrum of applications that range from green chemistry, catalysis, biotechnology, food, and medical industry to separation technologies and environmental engineering. ILs are organic salts that are in the liquid state at room temperature and by convention below 100°C. They exhibit a unique combination of properties such as extremely low vapor pressures, thermal stability, chemical tunability, good electrolytic, separation and solvation properties, non-flammability and easy recycling. The combination of these properties renders them ideal for use in a number of industrial applications such as solvents and catalysts in synthesis, as lubricants, as electrolytes in electrochemistry and in gas storage and CO₂ capture applications. The organic and simultaneously ionic nature of the constitutive ions results in diverse interactions that directly affect the microscopic structure and the dynamical behaviour of ILs. Molecular simulation methods are proven to be an extremely valuable means of reliable property prediction, enabling simultaneously the elucidation of the underlying mechanisms that are responsible for the macroscopic behavior of ILs aiming at the molecular design of task-specific materials and processes.

The present work focuses on the molecular simulation of imidazolium-based [TCM^-] ionic liquids in pure and in mixtures with CO₂ using an optimized and validated classical atomistic force field. Molecular simulations have been applied at various thermodynamic conditions and CO₂ concentrations up to high pressures. A wide range of properties such thermodynamic, structural, dynamic and transport properties have been calculated by performing very long molecular dynamics simulations at various ensembles and the effect of CO₂ concentration and of temperature on the above properties has been thoroughly investigated. Sorption isotherms and associated volumetric effects have been extracted using an multistage iterative scheme that incorporated MD simulations in the NPT ensemble and the Widom particle insertion method. The dynamics is enhanced as the CO₂ concentration is increased while simultaneously the viscosity is decreased in a self-consistent manner. The presence of CO₂ induces a decrease in the system’s molar volume, which is in very good agreement with experimental data in the same ionic liquid/CO₂ systems. The spatial organization of the ions even at high CO₂ concentrations remains rather uninfluenced by the presence of the gas molecules.