Nano-indentation of a room-temperature ionic liquid film on silica : a computational experiment

We investigate the structure of the [bmim][Tf2N]/silica interface by simulating the indentation of a thin (4 nm) [bmim][Tf2N] film by a hard nanometric tip. The ionic liquid/silica interface is represented in atomistic detail, while the tip is modelled by a spherical mesoscopic particle interacting via an effective short-range potential. Plots of the normal force (Fz) on the tip as a function of its distance from the silica surface highlight the effect of weak layering in the ionic liquid structure, as well as the progressive loss of fluidity in approaching the silica surface. The simulation results for Fz are in near-quantitative agreement with new AFM data measured on the same [bmim][Tf2N]/silica interface under comparable thermodynamic conditions.