Alkyl-Ethylene Amines as Effective Organic Friction Modifiers for Boundary Lubrication Regime.

With the pursuit of fuel economy in the automotive industry, recently low-viscosity lubricant technology has been widely improved. The present work has systematically discussed a series of sulfur- and phosphorus-free organic friction modifiers (FMs) - alkyl-ethylene amines by alkyl-substituted from ethylene amines with various nitrogen atom number and molecular configuration. Herein, the pin-on-flat reciprocation friction tests have exhibited that the addition of the novel alkyl-ethylene amines into base oil leaded to significant reductions in friction coefficient (up to 23 %). Further investigations of tribological properties at elevated temperature demonstrated that the increased number of nitrogen atoms and regular linear atomic arrangement contributed to an improvement of friction reduction (up to 66 %) compared to the neat base oil. Notably, results of water contact angle measurement and infrared spectroscopy (IR) have provided favorable evidences that the novel FMs have adsorbed on the metal surface leading to a formation of tribofilm. Whereby, the tribofilm has prevented the sliding surfaces from direct asperity contact and markedly improved tribological performance from the composition analysis of the worn surfaces by energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and confocal Raman spectroscopy. Therefore, the present work can provide practical reference for molecular structure design through investigation of structure-performance relations of lubricant additives.