Abstract
The influence of structural factors on the lubrication performance of organic friction modifiers (OFMs) formulated in Group V (polyol ester oil) base oil was studied using a ball-on-disk tribometer. The results show that OFMs can mitigate friction under heavy loads, low sliding speeds, and high temperatures. These conditions are commonly encountered in internal-combustion engines between cylinder liners and piston rings. The reduction in friction is ascribed to the boundary lubrication film containing the OFM. The chemical composition analysis of the metal disk surface using energy dispersive X-ray spectroscopy (EDS) confirmed the presence of a protective film of OFM on the wear track, albeit inconsistently deposited. Although the adsorption of the OFM on the metal surface was observed to be dependent on the chemical reactivity of the functional groups, levels of unsaturation, and hydrocarbon chain length of the OFM, the frictional performance was not always directly correlated with the surface coverage and tribofilm thickness. This implies that the friction reduction mechanism can involve other localized processes at the interface between the metal surface and lubricant oil. The occasional variation in friction observed for these OFMs can be attributed to the stability and durability of the boundary film formed during the rubbing phase.
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Acknowledgements
This study was funded by the Agency for Science, Technology and Research (A*STAR) under a Specialty Chemicals Advanced Manufacturing and Engineering IAF-PP research grant (Grant No. A1786a0026). We thank Yuchan LIU (Singapore Institute of Manufacturing Technology, A*STAR) for her assistance in the surface morphology measurements, and Kwek INEZ and Andrew Shin Boon LIM (Institute of Chemical and Engineering Sciences, A*STAR) for helping with SEM-EDX measurements. We gratefully acknowledge Croda, Singapore, for generously donating the base oil for this study.
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Febin CYRIAC. He received his B.Tech. degree in mechanical engineering from Anna University, India in 2008, and a dual master’s degree in rheology with specialization in polymer and materials engineering from University of Huelva, Spain, and University of Minho, Portugal in 2012 (Erasmus Mundus). He gained his Ph.D. degree from University of Twente, the Netherlands, majoring tribology in 2016. He is currently working as a scientist at the Institute of Chemical and Engineering Sciences, A*STAR, Singapore. His research interest covers many aspects of tribology, rheology, and surface characterization techniques. In 2018 he was honored Captain Alfred E. Hunt Memorial Award from STLE for authoring the best paper dealing with the field of lubrication.
Xin Yi TEE. She received her bachelor of science (honors) with major in chemistry & biological chemistry at Nanyang Technological University (NTU), Singapore, in 2017. She is currently a research engineer at Institute of Chemical and Engineering Sciences, A*STAR. Her research interests include rheology, tribology, and their application in the formulation of lubricant oils.
Sendhil K. POORNACHARY. He is a scientist in the Formulated Products Division at the Institute of Chemical and Engineering Sciences, A*STAR. He graduated with a B. Tech. in chemical and electrochemical engineering from Central Electrochemical Research Institute (CECRI), India, and an M.Tech. in chemical engineering from Indian Institute of Technology (IIT), Delhi. He obtained his Ph.D. in chemical and biomolecular engineering from the National University of Singapore (NUS) in 2008. His research interest lies in structure-property relationships in lubricant additives and surface characterization using spectroscopy and neutron/X-ray scattering techniques for correlating adsorption behavior and tribological performance.
Pui Shan CHOW. She received her B.Eng. degree in chemical engineering from the National University of Singapore in 1996 and a Ph.D. degree in chemical engineering from the University of Cambridge, UK, in 2000. She is the team leader of the Formulated Science Team within the Formulated Products Division at the Institute of Chemical and Engineering Sciences, A*STAR. Her research interest lies in the formulation of lubricant oils and structure-property relationships.
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Cyriac, F., Tee, X.Y., Poornachary, S.K. et al. Influence of structural factors on the tribological performance of organic friction modifiers. Friction 9, 380–400 (2021). https://doi.org/10.1007/s40544-020-0385-0
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DOI: https://doi.org/10.1007/s40544-020-0385-0