Study on the tribological properties of hexagonal boron nitride flakes composite hydrophilic/hydrophobic ionic liquids films by self-assembly

Abstract

Due to the weak out-of-plane van der Waals interaction between layers, hexagonal boron nitride (h-BN) with a stacking structure has been proven to be a promising lubrication material for its friction performance. However, obtaining h-BN composite films with excellent substrate bonding and low friction properties under high humidity remains challenging. Ionic liquids (ILs) composed of anions and cations that are liquid at or near room temperature have distinguished themselves in the field of lubrication (lubricating additives and lubricating films) due to their advantages of low saturated vapor pressure, good stability and high viscosity. Based on the relationship between lubrication performance and hygroscopicity of hydrophilic/hydrophobic ILs, a simple and flexible method for preparing h-BN composite hydrophilic/hydrophobic ILs films on metal substrates has been developed. h-BN has excellent antioxidant and moisture resistance as well as lubrication performance. Consequently, the influence of the hygroscopicity of ILs on the macroscopic tribological performance of h-BN composite hydrophilic/hydrophobic ILs films was investigated. The results showed that PVA/BNOH composite hydrophobic ILs films displayed a lower friction coefficient and outstanding wear resistance than those of PVA/BNOH composite hydrophilic ILs films in both atmosphere and high humidity. The synergies between the film layers, the intrinsic differences between the hydrophilic and hydrophobic ILs, and tribo-chemical reactions at friction interfaces greatly promoted the realization of excellent tribological performance of composite films. Additionally, the tribological properties of these films at high humidity were mainly related to the interaction between water molecules and the ILs.