engleski

Ionic liquids at interface

Understanding the molecular-level behavior of ionic liquids (ILs) at the boundary between the solid and liquid phases is of fundamental importance with respect to their application in, for example, electrochemical systems and electronic devices. We have studied the interfacial organization of an IL using a complementary combination of high-resolution X-ray reflectivity measurements and atomistic molecular dynamics (MD) simulations [1]. We used a model system consisting of a imidazolium-based cation with increasing alkyl chain length ([CnMim]+, n = 2, 4, 6) and a prototypical anion species ([NTf2 ]-), in contact with a sapphire substrate. Our strategy enables us to compare experimental and theoretically calculated reflectivities in a direct manner, thereby critically assessing the applicability of several force-field variants. On the other hand, using the best-matching MD description, we are able to describe the nature of the model IL−solid interface and physico-chemical characteristics in appreciable detail. More specifically, we characterized the three-dimensional layering profile of the ILs. We calculated interface-normal number density and charge density, total in-plane correlation functions and 2D histograms of the in plane position of ions in the first double layer. Changing the length of cation alkyl chain, we calculated the distribution and orientations of cations and anions in the first and the second layer. For each system we found the diffusivity constant in the bulk liquid and near the sapphire surface and compared how the changes in the force-fields affect the results.

ionic liquid ; nanoconfinement ; molecular dynamics simulations ; radial distributions ; interface-normal number density

Excellence Cluster “Engineering of Advanced Materials” at the FAU, DAAD project Multiscale Modelling of Supported Ionic Liquid Phase Catalysis (2017–2018)