Study of Wetting Behavior of BMIM+/PF6- Ionic Liquid on TiO2 (110) Surface by Molecular Dynamics Simulation

S Malali and M Foroutan, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 11226-11233 (2017).

DOI: 10.1021/acs.jpcc.6b12065

In the present work, wetting behavior of an ionic liquid droplet containing 1-methyl-3-butylimidazolium and fluorophosphate on the titanium dioxide (110) surface is studied using a molecular dynamics simulation. On the basis of the anisotropic characteristics of titanium dioxide surface, contact angles were calculated along different directions which are in agreement with experimental data. The obtained results show that a cation-rich layer is spread on the surface. Imidazolium rings of cations of ionic liquid are parallel to the titanium dioxide surface, but their orientation in the upper layer is almost vertical. Such positioning leads to the butyl-ring substituents locating at the top of the first layer to create a relatively empty space of cations while resulting in an anion-rich region. The cations and anions form a spherical shape on top of the first layer. Cross- sectional analysis of the ionic liquid reveals the circular configuration of cations and anions within the nanodroplet. The above observations signify the wetting behavior of the ionic liquid at the adjacent layer of surface and its nonwetting behavior at long distances from the surface which results in the formation of a spherical cap and is the direct consequence of the different behavior of cations and anions on the titanium dioxide surface.

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