In this work, the interactions between two key additives in current lubricants (ZDDP and MoDTC) and the effect on tribofilm formation and tribofilm evolution under boundary lubrication are studied. The chemical and tribological characteristics of the tribofilms are probed using measurement of friction, wear and film characteristics. Tribofilms have been examined by energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). In order to investigate the morphology of the reaction films formed, atomic force microscopy (AFM) was used. In this work, for the first time, a link between a proposed MoDTC breakdown mechanism and MoDTC tribofilm characteristics, measured on experimentally derived tribofilms, is made.

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Molybdenum DialkyldiThioCarbamate (MoDTC) is a friction modifier that has been used in automotive engines for many years. However, its exact decomposition mechanism within tribocontacts is not fully understood. In this study, an attempt has been made towards

ARTICLEThis journal is © The Royal Society of Chemistry 20xxJ. Name., 2013, 00, 1-3 | 1 This study aims to investigate the relationship between rheological and tribological properties of commercial full fat and fatfree/ low fat versions of liquid and soft solid colloidal systems (milk, yoghurt, soft cream cheese) with their sensory properties. Oscillatory measurements (strain, frequency), flow curves and tribological measurements (lubrication behaviour using Stribeck analysis) were conducted. Oral condition was mimicked using artificial saliva at 37 C. Discrimination test was conducted by 63 untrained consumers, followed by a qualitative questionnaire. Consumers significantly discriminated the fat-free/low fat from the full fat versions (p<0.01 -free samples. Flow behaviour of both versions of milk showed overlapping trends with no significant differences identified both in absence and presence of saliva (p>0.05). Full fat and fat free yoghurts had similar yielding behaviour and elastic modulus (G'), even in simulated oral conditions. However, in case of G low fat counterpart. Even in presence of artificial saliva, there was slight but significant difference in viscoelasticity between the cream cheese variants depending on fat content (p<0.05). Stribeck curve analyses showed that at lower entrainment velocities (1 100 mm/s), both full fat yoghurt and soft cream cheese exhibited a significantly lower traction coefficient when compared to fat-free/low fat versions (p<0.05), which might be attributed to the lubricating effect of the coalesced fat droplets. Surprisingly, whole and skim milks showed no significant difference in traction coefficients irrespective of the entrainment speeds (p>0.05). Results suggest that sensory distinction between fat-free and full fat versions, particularly in semi-solid systems could be better predicted by lubrication data as compared to bulk rheology. .

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