Doctor of Philosophy (PhD)
Ionic liquids (ILs) have sparked widespread interest due to their peculiar properties and the resulting possibility of manifold applications. In this dissertation, molecular dynamics (MD) simulations have been used to elucidate the dynamics, structure and crystallization of ionic liquids in the bulk and confinement. First we studied the properties of the ILs [dmim+][Cl-] and [emim+][NTf2-] when they are confined inside nanomaterials such as CMK-3, CMK-5 and an isolated amorphous carbon nanopipe (ACNP). The results indicate that the ions of the ILs form different layers inside these nanomaterials and their dynamics are slower due to the confinement. We also found significant differences in the densities and mobilities of ions caused by pore morphologies. Moreover, the presence of IL adsorbed in the outer surface of an uncharged ACNP in CMK-5 affects the dynamics and the density of an IL adsorbed inside the ACNP, and vice versa. Biased MD simulations have been performed to study the homogeneous nucleation of IL [dmim+][Cl-] from its supercooled liquid in the bulk, as well as the heterogeneous nucleation of the same IL near a graphitic surface. The string method in collective variables (SMCV) and Markovian milestoning with Voronoi tessellations, when used in combination with suitable order parameters proposed for molecular crystals, allow us to sketch a minimum free energy path (MFEP) connecting the supercooled liquid and crystal phases, and to determine the free energy and the rates involving in the nucleation processes. The physical significance of the configurations found along these MFEPs is discussed with the help of calculations based on classical nucleation theory, as well as simulation snapshots. Analogies and differences between both nucleation processes are analyzed and discussed. The simulation work described here is relevant to using ILs as electrolytes in energy-related devices, such as electrochemical double layer capacitors and dye-sensitized solar cells. Furthermore, nucleation of ILs is relevant to developing nanomaterials based on ILs.
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He, Xiaoxia, "Molecular Dynamics Simulation of the Structure, Dynamics and Crystallization of Ionic Liquids under Confinement and Low Temperature" (2015). LSU Doctoral Dissertations. 3929.