Low friction and wear self-assembly nano tribofilm of amphiphilic functionalized tea saponin in a water/oil phase

Developing an eco-friendly and energy efficient lubricant additive is important in the field of tribology. Herein, we successfully synthesized a series of green and efficient lubricant additives by grafting the n-carbon alkyl chain to tea saponin (TSCn, n = 8,10,12,14,16), nano tribofilm can self-assemble on sliding surfaces in both water and oil phases. Low frequency and high contact stress ball-on-disc reciprocating friction tests showed that TSC14 and TSC16 exhibit excellent lubricating performance. When 0.5 wt% of TSC14/TSC16 was added in DI water, the friction coefficient and wear rate were reduced by 67.69%/69.74% and 79.42%/81.65%, respectively. When 0.5 wt% of TSC14/TSC16 was added in PAO6, the friction coefficient and wear rate were reduced by 46.15%/42.86% and 86.19%/80.48%, respectively. In addition, the TSC14/TSC16 emulsion also exhibited good stability and lubricity. [Display omitted] •A series of functionalized tea saponin (TSCn, n=8,10,12,14,16) were obtained by grafting the n-carbon alkyl chains.•An effective soft-hard self-assembly nano tribofilm can form on sliding interface by TSC14 or TSC16.•TSC14 and TSC16 exhibit excellent lubricating performance in different lubricating media (DI water and PAO6).•The self-assembly tribofilm of TSCn has better tribology property than TS hydration layer or nanosheets deposition layer.