Probing the adsorption of the organic friction modifier GMO at the iron oxide-dodecane interface in situ with neutron reflectometry Alexander Armstrong 1,2 , Rui F. G. Apóstolo 3 , Thomas M. McCoy 2 , Finian J. Allen 1 , Rebecca J. L. Welbourn 1 , Robert Barker 4 ,Beatrice N. Cattoz 5 ,Peter J Dowding 5 , Philip J. Camp 3 and Alexander F. Routh 2 1 ISIS Neutron and Muon Source, UK, 2 University of Cambridge, UK, 3 University of Edinburgh, UK, 4 University of Kent, UK, 5 Infineum UK Ltd, UK Organic friction modifiers (OFMs) are amphiphilic molecules included in lubricant oils which decrease friction between highly loaded contacting surfaces. Over the past century a conventional OFM mode of action has been established, where OFM adsorption at metallic surfaces is thought to form compact surface films. These films are believed to form planes of low shear resistance between contacting metallic surfaces, reducing friction.[1] Probing the in situ interfacial structure of OFMs under engine-relevant conditions is challenging, and hence, in silico methods have been employed to explore the effects of lubricant structure on friction. Such studies have indicated that OFM surface coverage is a key factor in reducing friction under boundary conditions.[2, 3] However, the outcomes of these studies rely on the chosen initial film structure. Glycerol monooleate (GMO) is an organic friction modifier which has been the subject of previous simulation work[2], but the structure of self-assembled GMO at ferrous-oil interfaces is ill-defined. Neutron reflectometry (NR) is a scattering technique that can determine the film thickness of thin interfacial films in situ with Å resolution. NR is especially suited for studying films comprised of organic materials due to the different scattering of neutrons from hydrogen and deuterium. We have used this difference to resolve the self- assembled film of hydrogenated GMO that forms when an iron-coated silicon block is submerged in deuterated dodecane solutions. Some important considerations of the technique and analysis will be discussed, followed by a selection of results which detail the structure of adsorbed GMO under static and sheared conditions. References 1. H. Spikes, Tribol. Lett ., 2015, 60 :5. 2. J. P. Ewen, C. Gattinoni, N. Morgan, H. Spikes and D. Dini, Langmuir , 2016, 32 , 4450–4463. 3. M. Doig, C. P. Warrens and P. J. Camp, Langmuir , 2014, 30 , 186–195.
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