Molecular Structure Characteristics and Wetting Behaviors of Alkyl Binary Doped Ionic Liquids' Thin Lubricating Films on Silicon Surfaces: Molecular Dynamics Simulations

Abstract

The molecular structure characteristics and wetting behaviors of alkyl binary doped ionic liquids' (ILs) thin lubricating film on silicon surfaces, which are composed of a (DA) self-assembled monolayer (SAM) and a binary doped ILs layer, are probed by molecular dynamics simulations. In the binary doped ILs layer, 1-carboxyethyl-3-methylimidazolium chloride ([CMIM]Cl) ILs were bonded to the terminal amino (NH2) groups of the DA SAM, and 1-dodecyl-3-methylimidazolium hexafluorophosphate ([DMIM]PF6) ILs were distributed around the [CMIM]Cl molecules by physical adsorption. Additionally, surface coverage and chain grafting positions of the bonded-phase [CMIM]Cl and the adsorption properties of mobile-phase [DMIM]PF6 were investigated. The simulation results revealed that the optimal surface coverage of [CMIM]Cl on the DA SAM was 50% with a lateral spacing of 2a and a longitudinal spacing of 22a, in which a is the space between the adjacent molecules. Meanwhile, the optimal molecular ratio of [CMIM]Cl to [DMIM]PF6 was 1: 4, leading to the stablest structure of the lubricating film. Wetting behaviors of thin lubricating film on silicon surfaces showed good hydrophobicity, which is helpful for reducing friction and adhesion. It can be anticipated that the alkyl binary doped ILs' thin lubricating film is suitable for antifriction and antiadhesion applications on silicon surfaces.