MIE Distinguished Seminar Series: Robert Carpick, University of Pennsylvania | Nanoscale Factors Controlling Friction and Lubrication: From 2D Materials to Engine Oil*

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Date(s) - 12/10/2018

Mechanical Engineering Building, MC102

Nanoscale Factors Controlling Friction and Lubrication: From 2D Materials to Engine Oil

New insights into friction and lubrication from atomic force microscopy (AFM) are presented. First, nanocontacts with 2-dimensional materials like graphene are discussed, where friction depends on the number of layers. An initial model attributing this to puckering [1] is now enhanced by molecular dynamics (MD) simulations showing a strong role of energy barriers due to interfacial pinning and commensurability [2]. I will then discuss very recent results where AFM is used to develop new insights into practical lubrication mechanisms. We study zinc dialkyldithiophosphates (ZDDPs), which are highly effective anti-wear additive molecules used nearly universally in engine oils. We developed a novel AFM-based approach for visualizing and quantifying the formation of ZDDP anti-wear films in situ at the nanoscale. Film growth depends exponentially on temperature and stress, which can explain the known graded-structure of the films. Our findings provide new insights into the mechanisms of formation of ZDDP derived anti-wear films and the control of lubrication in automotive applications [3].

[1] C. Lee et al. Frictional Characteristics of Atomically-Thin Sheets. Science, 328, 76 (2010).

[2] S. Li et al. The Evolving Quality of Frictional Contact with Graphene. Nature 539, 541 (2016).

[3] N.N. Gosvami et al. Mechanisms of Antiwear Tribofilm Growth Revealed in situ by Single Asperity Sliding Contacts, Science, 348, 102 (2015).