The dynamic three-dimensional nanowetting
behavior of nanodroplets of three kinds of 1-ethyl-3-
methylimidazolium 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 per ion pair and silicon, and the Coulombic interaction of cations and anions varies
from −265.3 to −282.0 kJ/mol 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.