Dr. Robert Carpick, John Henry Towne Professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania in Philadelphia will give a seminar titled "Seeing the Hidden Interface: Revealing Nanoscale Mechanisms of Contact, Adhesion, and Friction by in situ Experiments" to the interested faculty and students at Discovery Park.

Abstract

As technology scales shrink, tribology plays an increasingly dominant role. This can be problematic (e.g., high friction and wear in micro/nano devices), or advantageous (e.g., using adhesion to drive nanostructure formation). The biggest challenge in exploring and exploiting these issues is that the interface between two materials is hidden from view. Recent advances in in situ methods have enabled tribological mechanisms at previously inaccessible interfaces to be studied with unprecedented resolution. I will discuss new science revealed by in situ experimental methods to develop physically-based insights into tribological processes. First, atomic force microscopy (AFM) is used to study anti-wear tribofilms derived from additives in lubricating liquids [1,2]. AFM in additive-containing oils monitors tribofilm growth, morphology, and properties in situ during single asperity sliding. The famous additive molecule zinc dialkyldithiophosphate (ZDDP) functions via surface-based nucleation, growth, and saturation of antiwear tribofilms [1,3]. New results will be presented showing that this works not only for pure ZDDP, but also for fully-formulated oils containing ZDDP and other additives. We then show that zirconia (ZrO2) nanoparticles can also form protective tribofilms, permitting more environmentally-friendly additives particularly for low viscosity lubricants [4,5]. Second, new insights into nanoscale adhesion and wear are achieved using in situ transmission electron microscopy (TEM) wear tests. A strong, reversible, sliding-history dependence of adhesion between silicon nanoasperities occurs, attributed to shear-induced removal of adsorbates [6,7]. I will also preview results applying the technique to study contact between two-dimensional materials including MoS2.

References
[1] N. N. Gosvami et al., Science, 2015, 348, 102-6, https://doi.org/10.1126/science.1258788
[2] N. N. Gosvami et al., Tribol. Lett., 2018, 66, 154, https://doi.org/10.1007/s11249-018-1112-0
[3] N. N. Gosvami et al., Trib. Int., 2020, 143, 106075, https://doi.org/j.triboint.2019.106075
[4] H. S. Khare et al., ACS Appl. Mat. Interf., 2018, 10, 40335-47, https://doi.org/10.1021/acsami.8b16680
[5] M. B. Elinski et al., Tribol. Lett., 2020, 68, 107, https://doi.org/10.1007/s11249-020-01346-1
[6] Z. B. Milne et al., Langmuir, 2019, 35, 15628-38, https://doi.org/https://doi.org/10.1021/acs.langmuir.9b02029
[7] J. D. Schall et al., Tribol. Lett., 2021, 69, 52, https://doi.org/10.1007/s11249-021-01431-z

Biography

Robert Carpick is the John Henry Towne Professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania in Philadelphia, PA. He studies nanotribology, nanomechanics, and scanning probes. He is a recipient of the AVS Nanotechnology Recognition Award, the ASME Newkirk Award, a R&D 100 award, and a NSF CAREER Award. He is a Fellow of the American Society of Mechanical Engineers, the American Physical Society, the Materials Research Society, the AVS, and the Society of Tribologists and Lubrication Engineers. He holds 10 patents and has authored over 200 peer-reviewed publications. Previously, he was a faculty member at the University of Wisconsin-Madison. He received his B.Sc. (University of Toronto, 1991) and his Ph.D. (University of California at Berkeley, 1997) in Physics, and was a postdoctoral researcher at Sandia National Laboratory. He served as Department Chair from 2011-2019, and since 2020 serves as the Director of Diversity, Equity, and Inclusion for his department.