Yongii Guan, Qunfeng Shao, Wenqiong Chen, Shimin Liu, Xiaoping Zhang, Youquan Deng. J Phys Chem C, 2017, 121(42): 23716-23726.
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The dynamic three-dimensional nanowetting behavior of nanodroplets of three kinds of 1-ethyl-3methylimidazolium ionic liquids (ILs) with radii between 10 and 30 Å is probed by molecular dynamics (MD) simulation on a solid silicon surface at temperatures ranging from 300 to 500 K. The simulation results show that contact angles change greatly and then tend to be saturated from 45° to 75° as the droplet radius of ILs varied from 10 to 20 Å and further to >20 Å. The values of the contact angle are anisotropic and could be 39.5° and 48.7° in the x and y directions of the droplets spreading on the solid silicon surface when the radius of the IL droplet is 10 Å, and increasing the radius of the droplets can weaken the anisotropy of the contact angle. Further analysis of the interaction among cations, anions, and silicon suggests that the van der Waals (VDW) interaction of ions and silicon substrate varies from −56.5 to −53.5 kJ mol-1 per ion pair and silicon, and the Coulombic interaction of cations and anions varies from −265.3 to −282.0 kJ mol-1 per ion pair as the droplet radius of ILs ranged from 10 to 30 Å. Upon increasing the droplet radius, the imidazolium ring of the cation in the adsorbed layer is more nearly parallel to the silicon substrate, and this allows a very effective interaction with the silicon substrate. These changes in the structure of the adsorbed layer in the vicinity of the silicon surface and their effects on the structuring of ions in the bulk liquid layers above this strongly adsorbed layer lead to the difference of VDW and Coulombic interactions as the droplet radius of ILs varied from 10 to 30 Å. Additionally, the impact of the intrinsic viscosity and temperature on the nanowetting behavior of ILs is also investigated.
Yongii Guan, Qunfeng Shao, Wenqiong Chen, Shimin Liu, Xiaoping Zhang, Youquan Deng. Dynamic Three-Dimensional Nanowetting Behavior of Imidazolium-Based Ionic Liquids Probed by Molecular Dynamics Simulation. J Phys Chem C, 2017, 121(42): 23716-23726.