Molecular Simulation of Homogeneous Nucleation of Ionic Liquids from the Melt

Crystallization of ionic liquids (ILs) can be used in the synthesis of optically-active (fluorescent) and magnetic nanomaterials based on ILs. However, very little is understood about the mechanism of nucleation of crystal phases, especially for ILs as most of their applications involve liquid phases. In this work we studied the homogeneous nucleation of crystals of the ILs 1,3-dimethylimidazolium chloride, [dmim⁺][Cl^-], and 1-butyl-3-methylimidazolium chloride, [bmim+][Cl-], from their supercooled liquid phase. We used the string method in collective variables [1] and the Voronoi tessellated milestoning method [2] to study the nucleation process of these ILs. Recently developed order parameters [3]for molecular crystals were used in conjunction with those methods, in order to detect local order in nm-sized regions and to distinguish between different crystal polymorphs and liquid/amorphous phases. Minimum free energy paths for the nucleation process, free energy barriers, mechanisms of nucleation, sizes of the critical nucleus and rates of nucleation for these ILs will be presented and discussed.

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[1] Maragliano, L.; Fischer, A.; Vanden-Eijnden, E.; Ciccotti, E. J. Chem. Phys. 2006, 125, 024106

[2] Vanden-Eijnden, E.; Venturoli, M. J. Chem. Phys. 2009, 130, 194101; Maragliano, L.; Vanden-Eijnden, E.; Roux, B. J. Chem. Theory. Comput. 2009, 5, 2589-2594

[3] Santiso, E. E.; Trout, B. L. J. Chem. Phys. 2011, 134, 064109

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