Molecular Dynamics Investigation of Structural Morphology of Reline Deep Eutectic Solvent in Bulk and Confinement
Supreet Kaur and Hemant K. Kashyap
Department of Chemistry, Indian Institute of Technology Delhi, Delhi
All-atom molecular dynamics simulations are applied here to describe the bulk and interfacial structure of reline, a deep eutectic solvent comprising choline chloride and urea in 1:2 molar ratio. The computed X-ray/neutron scattering structure functions and their partial components as well as real space correlations shows that both hydrogen bonding and long-range correlations between different constituents of reline play a crucial role to lay out the bulk structure of reline. The hydrogen bond donor species - urea - intervene the counter-ionic electrostatic interactions between cation and anion by forming strong hydrogen bonding interaction with Cl-. The investigation of reline in confinement, near neutral and charged graphene surfaces shows the presence of profound structural layering of not only the ionic components of reline but also the hydrogen bond donor species. In addition, depending on the electrode charge density, the choline ions and urea molecules render different orientations near the electrodes. The simulated number density and electrostatic potential profiles for reline clearly show the presence of multilayer structure up to a distance of 1.2 nm from the respective electrodes. Further, the observation of positive value of surface potential at zero charge (PZC) indicates the presence of significant non-electrostatic attraction between choline cation and graphene electrode. The computed differential capacitance Cd for reline exhibits an asymmetric bell-shaped curve, signifying different variation of Cd with positive and negative surface potential.
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