Relationship between the molecular structure of lubricants and appearance of anomalous film shapes in elastohydrodynamic lubrication conditions

Yagi, Kazuichi; Nishida, Kazuki; Sugimura, Joichi

doi:10.1016/j.triboint.2020.106574

Cited by 7 publications

(23 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…More specifically, the friction coefficient of the n-alcohols, carboxylic acids, amines, and chlorides increased sharply at low SRR and then decreased to very low values (μ < 0.01) at high SRR. 29 On the other hand, diols, triols, and phenols showed a gradual increase in friction coefficient with SRR, 29 as is typically observed for lubricant base oils. 7 In the liquid phase, competing hydrophilic and hydrophobic interactions cause short-chain nalcohols (e.g.…”

Section: Introductionmentioning

confidence: 77%

“…80 However, very high shear rates (300 s -1 ) were applied in this previous study 80 and so the observed differences may in fact due to frictional heating within the contact. 24 Yagi et al 29 showed that the friction of 1-dodecanol in glass-steel contacts increases to a maximum at low SSR, before decreasing with increasing SRR. Thus, in the tribometer experiments by Yagi et al 29 , there may have been a transformation from the high-friction to the low-friction polymorph at high SRR.…”

Section: Discussionmentioning

confidence: 99%

“…24 Yagi et al 29 showed that the friction of 1-dodecanol in glass-steel contacts increases to a maximum at low SSR, before decreasing with increasing SRR. Thus, in the tribometer experiments by Yagi et al 29 , there may have been a transformation from the high-friction to the low-friction polymorph at high SRR. Again, the possibility of the polymorphic transformation being driven by frictional heating, 24 rather than the shear stress, cannot be ruled out.…”

Section: Discussionmentioning

confidence: 99%

“…33 Tribology studies have suggested that solidification plays a central role to the unusual film formation and friction behaviour of n-alcohols under EHL conditions. 21,23,28,29 Upon solidification, long-chain n-alcohols are known to display polymorphism. 34 1-dodecanol has a melting point of 24 °C at atmospheric pressure.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Reddyhoff¹,

Ewen

Deshpande³

et al. 2021

Preprint

View full text Add to dashboard Cite

Simple <i>n</i>-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviour 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 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 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 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 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 macroscale superlubricity in an EHL contact lubricated by a non-aqueous 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.<br>

show abstract

Section: Introductionmentioning

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Reddyhoff¹,

Ewen

Deshpande³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…They found that the film thickening in the centre of the contact under high SRR conditions was smallest for 1-decanol (lowest melting point) and largest for 1-tetradecanol (highest melting point). Yagi et al 29 compared the EHL film formation and friction for a wider range of alcohols and related molecules. They found that linear monoalcohols, -carboxylic acids, -amines, and -chlorides produced anomalous film shapes and friction behaviour, while diols, triols, and phenols produced conventional EHL film shapes and friction behaviour.…”

Section: Introductionmentioning

confidence: 99%

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Reddyhoff

Ewen

Deshpande

et al. 2021

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

Simple n-alcohols, such as 1-dodecanol, show anomalous film-forming and friction behaviour in the elastohydrodynamic lubrication (EHL) contacts inside bearings and gears. Using tribometer, diamond anvil cell (DAC), and differential scanning calorimetry (DSC) experiments, we show that 1-dodecanol undergoes 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 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 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 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 dimple formation in the EHL films, suggesting that the anomalous film shapes are caused by the formation of rigid orthorhombic crystals inside the contact. The unusual friction and film-formation behaviour of 1-dodecanol result from bulk effects that are insensitive to the surface chemistry or topology. This is the first demonstration of macroscale superlubricity inside EHL contacts using a non-aqueous lubricant. 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. File list (2) download file view on ChemRxiv Alcohol Superlubricity paper-revised-clean.pdf (1.44 MiB) download file view on ChemRxiv Supporing Information-final.pdf (1.05 MiB)

show abstract

Influence of the Heat Transfer Field on Anomalous Lubricant Film Formation in Elastohydrodynamic Lubrication Conditions

2021

Self Cite

View full text Add to dashboard Cite

The in uence of the heat transfer eld on anomalous lm formation under elastohydrodynamic lubrication (EHL) conditions was studied. Liquid lubricant lm shapes between a transparent disc and steel ball friction pair were investigated by white light optical interferometry. 1-Dodecanol was used as the representative lubricant to develop anomalous lm shapes. A sapphire disc and glass disc, which have different thermal conductivities, were used as the transparent bounding surface. The heat transfer eld signi cantly in uenced the formation of anomalous lm shapes. The anomalous lm shapes approximated the shape of a conventional EHL lm with increasing ambient temperature. However, a thickened part of the lubricant lm remained, although the phase diagram of 1-dodecanol suggested it to be in the liquid state.

show abstract

Relationship between the molecular structure of lubricants and appearance of anomalous film shapes in elastohydrodynamic lubrication conditions

Cited by 7 publications

References 24 publications

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Macroscale Superlubricity and Polymorphism of Long-Chain n-Alcohols

Influence of the Heat Transfer Field on Anomalous Lubricant Film Formation in Elastohydrodynamic Lubrication Conditions

Contact Info

Product

Resources

About