Study of phosphonium based ionic liquid/dispersant additive interactions using spectroscopic technique for lubricant applications

Abstract

Fully formulated oils are used in the lubricant industry to enhance the effectiveness and efficiency in tribological contacts. Ionic liquids are currently being investigated as promising new additives and were formulated always with various additives to improve existing functionality of a base oil. However the interactions of ionic liquids with other additives have yet to be explored fully. In this work we have used 1H NMR, IR , DLS and UV–vis techniques to study the interaction of the phosphonium based ionic liquid trihexyl(tetradecyl)phosphoniumdecanoate (P66614 Dec) with the dispersant additives polyisobutylene succinic anhydride (PIBSA) and polyisobutylene succinimide (PIBSI) at a range of concentrations and temperatures. The effect of these ILs/dispersant interactions on steel tribo-surfaces was also assessed. The dispersant additive PIBSA and PIBSI was not only able to improve the miscibility of the P66614 Dec, further investigation showed that the ILs ion interaction was higher in the presence of PIBSA than PIBSI. This is proposed to be due to the differences in the dispersant head groups, with that of PIBSA resulting in more non-covalent interactions with P66614 Dec, resulting in the formation of a self-assembled dispersant shell over the IL, where the size of the nanoaggregates is smaller than the larger neat ILs aggregates. The tribology testing showed that the ILs/dispersant additives were able to reduce friction and wear as compared to the base oil but there was marginal difference in friction and wear response between PIBSA and PIBSI. The results of this study shows that the use of different dispersants is a viable method for understanding the additive interactions and how this improves the understanding about the ionic liquid associations and improved shelf-life in base oil.