Additive chemical structure and its effect on the wetting behaviour of oil at 100 °C

Abstract

In lubrication, additives are added to base oils to form surface layers that crucially improve its performance, particularly at high temperature. However, very little is known about their influence on the wetting behaviour of oil, even at room temperature, while for high-temperature, where the effects of the additives are the most intense, is absent. Accordingly, this work focuses on the additives’ effects on the wetting of oil on steel at 100 °C, which is relevant for the activity of most oil additives. Simple organic friction modifiers with different numbers of polar head groups, non-polar tail chain length, head-group polarity and saturation were investigated. The results show that additive-films change the steel surface, making it more oleophobic. Additives with one polar head group decrease the wettability by 98% more than the additives with two polar groups, the most-polar fatty acid by 75% more than the least-polar amine, the longest chain length of 18C atoms by 55% more than the shortest chain of 11 C atoms, and the unsaturated additive by 12% more than the saturated additive.