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Macroscale superlubricity and polymorphism of long-chain n-alcohols
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![]() | Accepted version | 1.41 MB | Adobe PDF | View/Open |
Title: | Macroscale superlubricity and polymorphism of long-chain n-alcohols |
Authors: | Reddyhoff, T Ewen, J Deshpande, P Frogley, M Welch, M Montgomery, W |
Item Type: | Journal Article |
Abstract: | Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviors under elastohydrodynamic lubrication (EHL) conditions, as found inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that liquid 1-dodecanol undergoes a pressure-induced solidification when entrained into EHL contacts. Different solid polymorphs are formed inside the contact depending on the temperature and pressure conditions. Surprisingly, at a moderate temperature and pressure, 1-dodecanol forms a polymorph that exhibits robust macroscale superlubricity. The DAC and DSC experiments show that superlubricity is facilitated by the formation of lamellar, hydrogen-bonded structures of hexagonally close-packed molecules, which promote interlayer sliding. This novel superlubricity mechanism is similar to that proposed for the two-dimensional materials commonly employed as solid lubricants, but it also enables the practical advantages of liquid lubricants to be maintained. When the pressure is increased, 1-dodecanol undergoes a polymorphic transformation into a phase that gives a higher friction. The DAC and DSC experiments indicate that the high-friction polymorph is an orthorhombic crystal. The polymorphic transformation pressure coincides with the onset of a dimple formation in the EHL films, revealing that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. This is the first demonstration of a macroscale superlubricity in an EHL contact lubricated by a nonaqueous liquid that arises from bulk effects rather than tribochemical transformations at the surfaces. Since the superlubricity observed here results from phase transformations, it is continuously self-replenishing and is insensitive to surface chemistry and topology. This discovery creates the possibility of implementing superlubricity in a wide range of machine components, which would result in enormous improvements in efficiency and durability. |
Issue Date: | 24-Feb-2021 |
Date of Acceptance: | 2-Feb-2021 |
URI: | http://hdl.handle.net/10044/1/87616 |
DOI: | 10.1021/acsami.0c21918 |
ISSN: | 1944-8244 |
Publisher: | American Chemical Society |
Start Page: | 9239 |
End Page: | 9251 |
Journal / Book Title: | ACS Applied Materials and Interfaces |
Volume: | 13 |
Issue: | 7 |
Copyright Statement: | © 2021 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsami.0c21918 |
Sponsor/Funder: | Royal Academy Of Engineering |
Funder's Grant Number: | RF\201920\19\269 |
Keywords: | Science & Technology Technology Nanoscience & Nanotechnology Materials Science, Multidisciplinary Science & Technology - Other Topics Materials Science friction superlubricity polymorphism elastohydrodynamic lubrication tribology 1-dodecanol 1-dodecanol elastohydrodynamic lubrication friction polymorphism superlubricity tribology Nanoscience & Nanotechnology 03 Chemical Sciences 09 Engineering |
Publication Status: | Published |
Online Publication Date: | 2021-02-10 |
Appears in Collections: | Mechanical Engineering Earth Science and Engineering |