Greases additised with phosphonium-based ionic liquids - Part I: Rheology, lubricant film thickness and Stribeck curves

Abstract

Two greases formulated with lithium complex and anhydrous calcium thickeners were mixed with cation phosphonium-derived ionic liquids with the aim of studying their rheology, lubricant film forming properties, and the friction behaviour under different temperatures and speeds. The addition of the ionic liquids decreased viscosity, yield stress, storage modulus and loss modulus of the greases, with larger effect on anhydrous calcium-based grease. The use of the ILs as additive affected the lubricant film thickness at increasing temperature and mainly in the low speed region. The viscosity reduction led to lower friction results under both temperatures and range of speeds tested. The trihexyltetradecylphosphonium decanoate ionic liquid had the higher influence on the abovementioned properties, especially mixed with the anhydrous calcium-based grease.