APS March Meeting 2024
Monday–Friday, March 4–8, 2024;
Minneapolis & Virtual
Session D29: Optimizing Soft Materials and Interfaces
3:00 PM–5:24 PM,
Monday, March 4, 2024
Room: 101J
Sponsoring
Unit:
DSOFT
Chair: Misaki Ozawa, Grenoble Alpes University
Abstract: D29.00011 : How Lubricant Wettability Influences Instabilities During Sliding Friction on Soft Solids*
5:00 PM–5:12 PM
Abstract
Presenter:
Hao Dong
(Lehigh University)
Authors:
Hao Dong
(Lehigh University)
Anand Jagota
(Lehigh University)
Chung-yuen Hui
(Cornell University)
Collaboration:
The authors thank Michael Andrew and Brian Bergman from Michelin North America for useful discussions.
Lubricated contacts in soft materials are of significant importance in various engineering and natural systems, such as tires, and haptic applications. Although the control of lubricated sliding friction is highly desired, the sophisticated interplay between a liquid lubricant and two solid surfaces makes the manipulation of friction a challenge. In general, there are three major lubrication regimes: boundary, mixed (ML), and elasto-hydrodynamic (EHL). In the boundary regime, liquid between contact surface pairs is squeezed out and, as a result, the sliding friction of the system is similar to that of its counterpart in dry contact. Different from the boundary regime in which solid mechanics dominates, in the ML and EHL regimes, which are very common in practical situations, deformation of the substrate and fluid flow are deeply entangled. One mechanism of the lubrication regime transition from EHL to ML regime is that the transition is accompanied by the generation of surface elastic instabilities. However, as a critical property of a liquid, its wettability of the solid surfaces, which can also strongly affect the lubrication regime transition and surface instability morphology, has been studied far less. More importantly, the correlation between these surface instabilities and lubricated sliding friction, especially the lubrication regimes in which the system is operated, still needs further investigation. In this work, we use an ultraviolet light-ozone (UV-Ozone) cleaner to treat a polydimethylsiloxane (PDMS) surface to enhance the wettability of glycerol on the PDMS surface. We demonstrate that increasing wettability of glycerol on PDMS substrates can maintain a liquid layer on solid surface more easily and hence decrease the lubricated sliding friction between the indenter and the substrate. By direct visualization for lubricated sliding, we find that the surface elastic instabilities have different morphologies and phenomena including wrinkles and stick-slip. These results reveal the contribution of wettability to the lubricated sliding friction as well as lubrication regime transition and provide a deeper understanding of ML regime.
*The authors acknowledge support from the National Science Foundation through the Grant LEAP-HI: CMMI-1854572.