Micro/nanotribological behaviors of ionic liquid nanofilms with different functional cations

Abstract

Four kinds of molecularly thin films of room temperature ionic liquids (RTILs) with different functional cations were prepared on silicon substrates by dip-coating method. Thermal stability of the RTILs was evaluated using Mettler thermal gravity analysis (TGA) in a nitrogen atmosphere. Chemical compositions of the RTIL nanofilms were examined by means of multifunctional XPS. Nanoscaled adhesion and friction forces between the films and AFM tip were measured by FFM whereas the morphologies of the films were also investigated. Microscaled friction and wear behaviors between the films and Si 3 N 4 ball were further measured by the microtribometer. The micro/nanotribological behaviors of different RTIL films were comparatively investigated and discussed in terms of functional cations of the RTILs molecules. Results in this paper revealed that the functional cations of the RTIL films significantly affected their tribological behaviors both in micro-and nanoscales. The corresponding micro/nanotribological mechanism of the tested ultrathin RTIL films under the test conditions was consequently proposed based on the experimental results.

Ionic Liquid Nanotribology: Stiction Suppression and Surface Induced Shear Thinning

“…Their nanoscale friction coefficients obtained from AFM with a Si 3 N 4 tip were in the range of 0.02–0.05. Recently, Wang et al used AFM with a silicon cantilever to perform measurements on another group of imidazolium ILs finding slightly higher values of μ ≈ 0.04–0.1. Mo et al. , used colloid probe AFM with a silica probe to evaluate the performance of imidazolium type ILs on silicon surfaces (and modified silicon surfaces) and again determined similar values of μ ≈ 0.09–0.13.…”

“…As mentioned above, previous work focuses on adsorbed thin films of ILs, ,,, whereas in our experiments, the entire system (probe + substrate) was immersed in the IL. A potential problem with thin films is that they may locally be depleted, exhibiting a gradual increase in μ and they may also be more subject to water adsorption from the atmosphere .…”