Viscosity of Nanoconfined Fluids and the Effect on Elastohydrodynamic Lubricated Interfaces

by Michelle Len

Institution: University of California – Merced
Year: 2016
Keywords: Mechanical engineering; EHL; elastohydrodynamic lubrication; lubrication; nanoconfinement; squalane; viscosity
Posted: 02/05/2017
Record ID: 2131506
Full text PDF: http://www.escholarship.org/uc/item/2qw846j7


The elastohydrodynamic lubrication (EHL) regime is characterized by the elastic deformation of the bodies in contact, hydrodynamics of viscous friction caused by shearing the lubricant, and dramatic viscosity increase due to high pressure. As technology for mechanical components advances towards higher energy efficiency and less energy loss from viscous friction, this advancement implies that lubricant films are decreasing towards thicknesses on the nanometer scale. However, these lubricant films may behave differently from what is predicted by classical EHL theory. While viscosity is affected by temperature, pressure, and shear rate, researchers have discovered that there is a new dependence of film thickness on viscosity, indicating that extreme confinement in EHL can affect the viscosity of the lubricant. In this work, we attempt to characterize the relationship between film thickness and viscosity for squalane using molecular dynamics (MD) simulations so that we may observe how the lubricant behaves with film thicknesses on the nanometer scale. However, we were unable to successfully obtain this relationship due to issues with the MD simulations. In addition, we attempt to improve the ability of EHL simulations to accurately capture the behavior of ultra-thin film lubricated interfaces by incorporating empirical models that describe the effect of confinement on fluid viscosity. The enhanced model reproduces trends seen in some EHL experiments where the film thickness of very thin film lubricants is larger than expected compared to classical EHL theory. Our enhanced EHL simulation successfully produces film thickness results with increased accuracy to experimental data.