Micro–nano behaviour of DMBI-PF₆ionic liquid nanocrystals: large and small-scale interfaces

Abstract

Microelectrical mechanical systems (MEMS) devices coated with a thin film of ionic liquid showed significant improvement in wear life. These promising tribological findings led to the current study of the micro-nano behaviour of an ionic liquid, 1,2-dimethyl-3-butyl imidazolium hexafluorophosphate (DMBI-PF 6 ), when applied as a thin film on a polished silicon surface. The films remain as microdroplets in ambient conditions but undergo drastic changes when agitated by an atomic force microscope (AFM) contact scan or touched with a biased AFM tip. The nanotribological characteristics including mobility, diffusion and scratch resistance are studied. In the case of DMBI-PF 6 , it was observed that the imidazolium ion is a mobile phase while PF 6 is attached to the silicon surface. Crystallites are formed as a result of tip contact and depend on the tip bias and environmental conditions. Crystallization of DMBI-PF 6 from the liquid phase with no tip bias showed substantial variation in crystal shape compared to those formed under the influence of an electric bias.

A Review of Ionic Liquids for Green Molecular Lubrication in Nanotechnology

“…For the monocationic BMIM-PF 6 , only weak interactions between the imidazolium ring and the silicon surface are expected. This is similar to the proposed mechanism by Nainaparampil et al [26], where the imidazolium cation was considered as mobile, while the anion is the species responsible for attachment to the silicon substrate. However, for the dicationic ILs, multiple cation attachment schemes are possible.…”

“…Other applications include supercritical fluids, active pharmaceutical ingredients, as well as heat transfer fluids [18][19][20][21]. ILs have been investigated over the last decade for lubrication applications [17,[22][23][24][25][26][27][28][29][30][31][32]. Similar to PFPEs, ILs exhibit high temperature stability, low vapor pressure, and desirable lubrication properties.…”

Ultrathin Wear‐Resistant Ionic Liquid Films for Novel MEMS/NEMS Applications

“…To date, the friction behavior of materials coated with ionic liquids is known only at the microscale from studies using conventional ball-on-disk or pin-on-disk tribometers. [16,17,21,22,23,25,27] Adhesion and friction properties at the microscale can be different from the nanoscale. [28] Knowledge of the latter is important in optimizing lubrication of MEMS/NEMS devices.…”

Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

“…The difference in the degradation steps of the anion on different substrates could be linked to the bond strength between the anion and the substrate. The anion can be immobilized on a hydroxyl-terminated oxide surface by strong covalent bonding [27,33,69,70], while on a partly oxidized metal surface only physical or chemical adsorption and hydrogen bonding occur. A covalently bonded anion can be subjected to larger strain under interfacial shearing and undergo more significant degradation than an adsorbed anion.…”