Preparation and tribological properties of organically modified graphite oxide in liquid paraffin at ultra-low concentrations

In recent years, two-dimensional (2-D) materials have attracted more and more attentions due to their 2-D anisotropy and special physicochemical properties. In this work, hexadecyltrimethoxysilane (HDTMS) and octyltrimethoxysilane (OTMS) were employed to modify graphite oxide (GO) nanosheets for potential applications as lubricating oil additives. The organically modified GO nanosheets were characterized by FTIR, XRD, TGA, UV-vis spectroscopy and SEM, which indicated that HDTMS and OTMS had successfully entered the GO layers. Furthermore, the tribological properties of liquid paraffin containing HDTMS and OTMS modified GO were investigated by a four-ball friction testing machine. The results show that ultralow concentration (0.008 wt%, the optimal value) of HDTMS or OTMS modified GO in liquid paraffin can reduce the friction coefficients of the mixtures by 34.0% and 15.5% respectively. HDTMS, which possesses longer alkyl chains, is better for improving the organic compatibilities and helps GO nanosheets to exfoliate more significantly and disperse in paraffin more homogeneously, thus corresponding to better effectiveness in decrease the friction coefficient.