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

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 behavior 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 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 above-mentioned properties, especially mixed with the anhydrous calcium-based grease.

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The authors are grateful to the Principality of Asturias (Spain) for granting the research project LuSuTec (IDI/2018/000131) under which this research was developed. The authors also acknowledge the Ministry of Science, Innovation and Universities for supporting the research stay (ref.: CAS19/00290) of Marlene Bartolomé at the Universidade do Porto (Portugal) under the framework of the programme “José Castillejo”. The authors gratefully acknowledge Axel Christiernsson International AB (Nol, Sweden) for supplying the tested greases in this study.