Tribological performance of protic ionic liquids containing dibutyldithiophosphate as lubricating additives in O/W emulsions

A series of protic ionic liquids (PILs) containing dibutyldithiophosphate were simply synthesised and used as lubricant additive in base emulsion. The physico-chemical and lubricating properties of PILs in emulsion were systematically investigated. The stability of prepared emulsions containing PILs were similar with base emulsions by particle size distribution tests. Compared with traditional additive of polysulfide, the PILs in emulsion exhibited superior lubricating properties under harsh conditions. Surprisingly, the oil-miscible O-PILs in emulsion showed better friction and wear reduction than water-miscible T-PILs in emulsion. The stable protective films formed on the steel surface by results of scanning electron microscope and X-ray photoelectron spectroscopy were the main reason for the preferable performance.