WEB In-situ studies of the competitive adsorption of lubricant additivesTuesday (22.09.2020) 16:50 - 17:20 S: Structural Materials 2 Part of:
Since the pioneering studies by Spikes in the 1980s, research towards the understanding of adsorption mechanisms of lubricant oil additives gained significant attention (see e.g. [1,2]). The proposed models are mostly based on ex- and post-mortem studies or simulations. Here, we present in-situ adsorption studies, using a quartz crystal microbalance with dissipation QCM-D.
The QCM-D is a nanogram-sensitive technique to study adsorbed amounts (from frequency information) and viscoelastic properties (from dissipation) of the adsorbed molecules. Using QCM-D we measured the frequency and dissipation shift during adsorption of a friction modifier on an iron oxide surface from mineral base oil. The frequency decreases after the lubricant change from base oil to base oil + additive, which indicates a mass increase (adsorption). The dissipation increases after switching, so the adsorbed additive film shows an increased viscoelasticity compared to the pure base oil. Interestingly, by changing the medium back to pure base oil the frequency decreases and the dissipation unexpectedly increases again. The QCM-D gives no information exceeding quantitative adsorption and viscoelasticity. To observe the morphology of the adsorbed addditive layer we used an in-situ imaging method based on fluorescence. The combination of both methods gives interesting new insights in the behavior of lubricant oil additives on surfaces.
 Spikes, H. A. (1989): Additive-additive and additive-surface interactions in lubrication. In: Lubr. Sci. 2 (1).
 Bernat, S.; Armada, S.; Espallargas, N. (2018): Friction Mechanisms by Carboxylic Acids in Aqueous Lubricants. In: Tribology Letters 66 (3), S. 83. DOI: 10.1007/s11249-018-1035-9.
 J. Honselmann, M. Dienwiebel, T. Rühle, T. Umbach, W. Grabarse (2018): “Correlation of adsorption behavior and performance of corrosion inhibitors in synthetic base oils”. GETLUB 5. Internationaler Schmierstoffkongress. Hamburg, Forschungsvereinigung Antriebstechnik e.V.
 K.O. Evans (2010): “Quartz crystal microbalance investigation of the structure of adsorbed soybean oil and methyl oleate onto steel surface,” In: Thin solid films, v. 519, no. 2, pp. 900-905