(214i) Structure, Dynamics and Crystallization of Ionic Liquids in the Bulk and Under Confinement

In this poster we show results from two directly related projects. In our first project, molecular dynamics simulations were used to study the structure and dynamics of the ionic liquid (IL) [bmim⁺][NTf₂^-] confined inside the ordered mesoporous carbons CMK-3 and CMK-5, which consist of nanorods and nanopipes made of amorphous carbon. This material exhibits interconnected nanopores, which are promising candidates for applications in electrochemical double-layer capacitor (EDLCs). Our results indicate that variables such as pore size, pore morphology, temperature and surface density of electrical charges have a profound influence on the structural and dynamical properties of the confined IL. Ions inside the pore form different layers, with the number of layers and liquid structure varying with pore size, pore morphology and surface charge density. The dynamics of the ions far away from the surface of CMK-3 and CMK-5 are significantly faster than that of the ions near the carbon surfaces; in particular, increases in surface charge density leads to a significant reduction in the mobility of the counterions in the layers near the carbon walls.  

In our second project we focus on novel nanomaterials based on frozen ILs. These nanomaterials hold enormous promise, as they exhibit the highly tunable properties of ILs. However, the design of crystalline materials is complicated because many molecules can crystallize into different polymorphs, which frequently exhibit different physical properties that affect their suitability for specific applications. To gain a molecular-level understanding of how cations and anions in an IL organize themselves into crystal structures, here we performed computer simulations of crystallization of the IL [dmim⁺][Cl^-] in the bulk. We used the string method in collective variables to determine minimum free energy paths (MFEPs) for crystal nucleation. Novel order parameters based on the generalized pair distribution function were used to characterize the different states connecting the liquid and crystal phases along the MFEP. The calculations also provide insights about activation barriers and the mechanisms of nucleation in these systems.