2016-04-22 11:00:00 2016-04-22 12:00:00 America/Indiana/Indianapolis Center for Materials Processing and Tribology Distinguished Seminar - Carpick Robert Carpick, the John Henry Towne Professor, Dept. of Mech. Eng. & Applied Mechanics, University of Pennsylvania, will present a seminar on "Nanoscale Factors Controlling Friction and Lubrication: From 2D Materials to Engine Oil". Potter 234 (The K.S. Fu Room)
April 22, 2016
Center for Materials Processing and Tribology Distinguished Seminar - Carpick
| Event Date: | April 22, 2016 |
|---|---|
| Hosted By: | Center for Materials Processing and Tribology Distinguished Seminar |
| Time: | 11:00 AM |
| Location: | Potter 234 (The K.S. Fu Room) |
| Contact Name: | Srinivasan Chandrasekar, Professor, School of Industrial Engineering |
| Contact Email: | chandy@purdue.edu |
| Priority: | No |
Robert Carpick, the John Henry Towne Professor, Dept. of Mech. Eng. & Applied Mechanics, University of Pennsylvania, will present a seminar on “Nanoscale Factors Controlling Friction and Lubrication: From 2D Materials to Engine Oil”.
Refreshments will be served at 10:50 AM
Abstract
Although tribological processes — friction, adhesion, lubrication, and wear are common and important phenomena, we lack well-grounded scientific theories to explain or predict them. Such understanding would allow the development of rational strategies for reducing energy dissipation and increasing reliability at all length scales, enabling applications, such as micro-/nano-electromechanical systems (MEMS/NEMS), where friction and wear are primary limitations. I will discuss recent studies of nanoscale friction/ lubrication that reveal surprising new behavior and insights obtained using AFM.
First, the behavior of nanoscale contacts with 2-dimensional materials will be discussed. For nanoscale
contacts to graphene, the friction force exhibits a significant dependence on the number of 2-D
layers, which we attribute to a puckering mechanism arising from the increased tendency of thinner materials
to adhere to the sliding tip [1]. An even stronger effect occurs when graphene is fluorinated, where
experiments and molecular dynamics simulations consistently show that friction between nanoscale tips
and fluorinated graphene (FGr) monolayers exceeds that for pristine graphene by an order of magnitude.
The results can be interpreted in the context of the Prandtl-Tomlinson model of stick-slip friction, where
static friction arises from the high electronic roughness of fluorinated graphene [2]. This demonstrates
how corrugation of potential energy is key to controlling atomic-scale friction.
Second, I will 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. ZDDPs function by breaking down
under the combination of contact stress and temperature to form wear-resistant protective films on the
steel surfaces. However, the generation of phosphorous- and sulphur-containing compounds reduces
the working life of the catalytic converter, motivating studies to understand how ZDDPs work so that
its use can be reduced or eliminated. 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].
Bio-sketch
Robert Carpick is the John Henry Towne Professor, Dept. of Mech. Eng. & Applied Mechanics, University
of Pennsylvania, where he has served as Department Chair since 2011. Previously, he was a faculty member
at the University of Wisconsin-Madison (2000-2007). He received his B.Sc. from the University of Toronto (1991),
and his Ph.D. from the University of California at Berkeley (1997), both in Physics, and was a postdoc at Sandia
National Laboratory (1998-1999). He studies nanotribology, nanomechanics, and scanning probes. He is the recipient
of a NSF CAREER award (2001), the ASEE Outstanding New Mechanics Educator award (2003), the ASME
Newkirk award (2009), an R&D 100 Award (2009), and is a Fellow of the American Physical Society, the American
Vacuum Society, and the Society of Tribologists and Lubrication Engineers. He holds 4 patents and has authored
over 140 peer-reviewed journal publications.
[1] C. Lee, Q. Li, W. Kalb, X-Z. Liu, H. Berger, R. W. Carpick, and J. Hone. Frictional characteristics of atomically thin sheets.
Science, 328(5974):76–80, 2010.
[2] Q. Li, X-Z. Liu, S-P. Kim, V. B. Shenoy, P. E. Sheehan, J. T. Robinson, and R.W. Carpick. Fluorination of graphene enhances
friction due to increased corrugation. Nano Letters, 14(9):5212–5217, 2014.
[3] N. N. Gosvami, J. A. Bares, F. Mangolini, A. R. Konicek, D. G. Yablon, and R.W. Carpick. Mechanisms of antiwear tribofilm
growth revealed in situ by single-asperity sliding contacts. Science, 348(6230):102–106, 2015.