Influence of Chain Length on the Micro/nano-tribological Properties of Ionic Liquid Nano-films

Ultra-thin RTILs films with different chain lengths were successfully prepared on silicon substrates　by a dip-coating method. The influence of different chain length on micro/nano-tribological properties of the as-prepared RTILs films was systematically investigated. Thermal stability of the RTILs was evaluated using a Mettler thermal gravity analysis in a nitrogen atmosphere. Chemical compositions of the films were characterized with a multi-functional X-ray Photoelectron Spectrometer. Wetting/dewetting properties were determined by a contact angle measure instrument. The morphologies, nano-friction and nano-adhesion behaviors of RTILs films with different chain lengths were experimentally investigated at the nanoscale using AFM/FFM.　Microfriction properties were evaluated by a microtribometers. The investigation revealed that the chain length of the RTILs films significantly affected their nano-friction and adhesion properties, but had little influences their microfriction performance. With the increasing chain length, adhesive force and nanofriction force reduced significantly. The corresponding friction-reduction and anti-wear mechanisms of the tested ultra-thin RTILs films under tested condition were analyzed based on the experimental observation.