Novel binary oil-soluble ionic liquids with high lubricating performance

In this work, the functional protic ionic liquid (PIL) of dibutylammonium 3-(methylthio) propionate ([N44HH][MTP]) with good lubrication properties but poor oil solubility and the common PIL of dioctylammonium oleate ([N88HH][OA]) with good oil solubility but poor lubricating performance were selected. The binary ionic liquid (BIL) of [N88-N44][OA-MTP] was creatively obtained by combining [N44HH][[MTP] with [N88HH][OA]. Interestingly, the BIL has good oil solubility in PAO base oil and maintains outstanding lubricating performance, indicating that such an approach improves the oil solubility of functional PILs without worsening lubrication properties. In addition, the compatibility between two PILs and the lubrication mechanism of the BIL system were analyzed and described by means of several analytical methods. • One novel approach was first improved for improving the oil solubility of functional ionic liquids. • One oil-soluble binary ionic liquid (BIL) was synthesized. • The BIL exhibited outstanding antiwear and friction-reducing performance. • The lubrication mechanism of BIL was analyzed.