Microtribological properties of a spin-coated thin film of 1-butyl-3-(propyltrimethoxysilane)imidazolium bis(mandelato)borate ionic liquid

Abstract

A thin film of 1-butyl-3-(propyltrimethoxysilane)imidazolium bis(mandelato)borate (BPtmSiIm-BMdB) ionic liquid was prepared by spin coating on a silicon surface. XPS results suggested the covalent interaction between trimethoxy groups of BPtmSiIm-BMdB ionic liquid and hydroxyl functionalities of the silicon surface, and afforded a good quality thin film. The microtribological properties of the BPtmSiIm-BMdB thin film were probed under the mean Hertzian contact stress of 0.29–0.53 GPa. The BPtmSiIm-BMdB thin film exhibited significantly low and steady friction (μ = 0.06 to 0.10) at variable loads compared to bare silicon (μ = 0.6). The low coefficient of friction and remarkable wear-resistivity of the BPtmSiIm-BMdB thin film were collectively attributed to (a) strong adherence of ionic liquid on the silicon surface, (b) a layered structure of the ionic liquid driven by coulombic interactions, (c) a rigid and compact structure of the chelated bis(mandelato)borate anion, (d) tribo-induced deposition of ionic liquid on the counter steel ball and (e) the presence of flowable fraction of the ionic liquid with a self-replenishment property. This study demonstrates a good prospect for ionic liquid thin films, which have a stable and good foundation on the underlying surface.