2D Ni-BDC-stabilized Pickering emulsion for enabling friction-reducing application

Abstract

The issue of poor dispersion stability of 2D nanomaterials in lubricants has always constrained their practical applications. Owing to the adjustable hydrophilicity and lipophilicity on the surface of two-dimensional metal–organic frameworks (2D MOFs), Pickering emulsions can not only achieve long-term dispersion stability of 2D MOFs, but also help reveal the friction mechanism of 2D nanomaterials without modification. In this work, we constructed a novel two-dimensional nickel-benzene-1,4-dicarboxylate metal–organic framework (2D Ni-BDC)-stabilized Pickering emulsion. The effect of the oil-to-water ratio and the content of 2D Ni-BDC on the properties of the Pickering emulsion was investigated. Characterizations corroborated the presence of 2D Ni-BDC nanosheets at the emulsion interface. The tribological behavior of the 2D Ni-BDC-stabilized Pickering emulsion, depending on reciprocating frequency and applied load, was investigated using a reciprocating friction tester. The content of 2D Ni-BDC obviously influenced the friction coefficient and wear rate of the emulsion, attaining the minimum values at 2.8 wt% with a 61.1% reduction in the friction coefficient and a 67% decrease in the wear rate relative to pure water. The investigation of sliding frequency and load indicated that a lower frequency and higher load contributed to achieving a lower friction coefficient and wear rate. Lastly, worn surface analysis disclosed the lubrication mechanism of the 2D Ni-BDC-stabilized Pickering emulsion.