Boundary lubricating films: formation and lubrication mechanism

Hsu, Stephen M.; Gates, Richard S.

doi:10.1016/j.triboint.2004.08.021

Cited by 195 publications

(101 citation statements)

References 21 publications

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“…The lower friction in that case could be due to the presence of a sacrificial boundary layer, 31 whereas in our case, saliva in its hydrated form can behave like a gel allowing boundary sliding between two interfacial salivary films similar to what is proposed by Hsu and Gates. 31 Is influencing friction the only role saliva plays in inmouth lubrication? Saliva consists mainly of glycoprotein, mucins, which are highly surface-active and can form stable emulsions in the presence of oil.…”

Section: Discussionsupporting

confidence: 74%

Tribology of o/w Emulsions Under Mouth-like Conditions: Determinants of Friction

et al. 2007

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Fat-perception is thought to be related to a complex interplay between fat-associated flavor release and mouth-feel. Friction sensed between the tongue and the palate seems to play a prominent role: in previous work, we have shown that emulsions that are more sensitive toward coalescence give rise to a lowering of the orally perceived and experimentally measured friction and, probably as a consequence, to an enhanced fat-perception. In this paper, we study in detail the factors determining friction of protein-stabilized emulsions using a novel mouth-mimicking tribometer and model surfaces consisting of PDMS modified in various ways (hydrophobicity, deformability, roughness). We show that unlike in many technological applications where lubrication is essentially hydrodynamic, for physiologically relevant loads, the modified PDMS is boundary and/or mixed lubricated, which is like in-mouth lubrication. We find that an increased sensitivity of the emulsions toward coalescence results in a lower friction, confirming previous results obtained with pig's tongue. Surface-induced coalescence (or spreading of emulsion droplets) seems to be very important in this, surface hydrophobicity being the dominant trigger. Viscosity of the dispersed phase does not have such a strong influence on both the measured friction and the oral perceived friction. We do find a strong influence of the presence of bulk proteins and saliva on friction. Finally, hardly any dependence of measured friction on fat content of the emulsion was observed, indicating that only a small amount of fat is needed to alter the friction.

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Section: Discussionsupporting

confidence: 74%

Tribology of o/w Emulsions Under Mouth-like Conditions: Determinants of Friction

et al. 2007

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“…As a consequence, the increase of contact angles should occur with the increase of the content of this metal [24,25]. For high temperature, generally the contact angle of hydrogenated coatings was lower than for hydrogen-free ones.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…It was surprising, since metals typically decompose carbohydrates of oil producing polar species such as carboxylic acid, which are absorbed at the surface and forms metallic compounds [24,25] . These compounds should increase the friction coefficient.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Carbon-based coatings doped by copper: Tribological and mechanical behavior in olive oil lubrication

Balestra

Castro

Evaristo

et al. 2011

Surface and Coatings Technology

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We deposited C-based films doped with Cu and tested their sliding properties in olive oil as environment-friendly lubricant, which can be used in many mechanical systems, particularly in agriculture engineering. The coatings were deposited in a four unbalanced magnetron sputtering device combining C and C/Cu targets; argon (hydrogen-free films) and Ar/CH 4 (hydrogenated films) atmospheres were used. Cu content of the films was in the range 5-14 at.%. The hardness of the films was almost constant whatever the Cu content was. On the other hand, hydrogen-free coatings were much harder (about 15 GPa) than hydrogenated ones (about 4 GPa). The coatings were oleophilic and their sliding properties were evaluated using ball-on-plate tests with 200000 cycles. The non-hydrogenated coating with 6 at.% of copper showed the best tribological performance with negligible wear for all olive oil testing temperatures (i.e. up to 120 °C).

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“…ZDDP가 갖는 뛰어난 마모억제, 산화방지, 열 안정성 등의 기능들로 인하여 수년간에 걸쳐 다수의 논문과 특허에서 ZDDP에 대 해 다루고 [3][4][5][6][7][8][9][10][11][12][13][14], 이러한 마모억제 기능을 갖는 첨가제들의 작용 메커 니즘이 어떻게 이루어지는지에 대해 연구해왔고 다루고 있다 [15][16][17][18][19][20][21][22].…”

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“…일반적으로 ZDDP와 같은 첨가제가 경계 또는 혼합 윤활에서 높은 부하 및 온도의 극단적인 조건 하에서 분해되면서, 분해생성물과 화 학 반응 또는 흡착 프로세스에 의해 마찰이 발생하는 표면에서 경계 면을 보호할 수 있는 마모억제 기능을 갖는 표면 막을 형성한다 [1,18,[21][22]. 이러한 표면에 형성된 얇은 막인 tribofilm은 마모를 줄 이기 위해 직접 금속이 접촉되는 표면에서 요철의 용착을 방지하는 기능을 한다 [1].…”

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A Study on Dimethacryloyloxy Alkane Derivatives Having an Anti-wear Performance as Lubricating Oil Additives

Han¹,

Cho²,

Sim³

et al. 2016

Applied Chemistry for Engineering

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Lubricant additives including zinc dialkyldithiophosphate (ZDDP) containing metal have been widely used due to the advantage of very low cost, but they can generate impurities such as ash. In this work, ZDDP containing metals was partially replaced with bis[3-(dialkyloxyphosphorothionyl) thio-2-methylpropanyloxy] butane (BAP4s) which was synthesized conveniently and effectively from alkanediol without any metal components. Also, the wear resistance property of synthesized BAP4s were studied. Wear scar diameter (WSD) values of BAP4s with butyl, octyl, decyl, dodecyl or tetradecyl groups were also measured by four-ball test. As the length of the alkyl group increased from 4 to 8, the WSD value of BAP4s decreased rapidly from 0.59 to 0.45 mm, but from 8 to 14, the value increased very slowly from 0.45 to 0.50 mm. Thus, among all BAP4s, B8P4 having BAP4 with the octyl group, showed the lowest WSD value. Furthermore, the WSD values were measured in a lubricant base oil mixed with a 0.50 percent concentration (w/w) of either BAP4 or ZDDP. The former was 0.55 mm, and the latter was 0.45 mm. The thermal stability and tribofilm formation peroperty were also measured by thermogravimetric analyzer (TGA) and energy-dispersive X-rays spectroscopy (EDS), respectively.

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Boundary lubricating films: formation and lubrication mechanism

Cited by 195 publications

References 21 publications

Tribology of o/w Emulsions Under Mouth-like Conditions: Determinants of Friction

Tribology of o/w Emulsions Under Mouth-like Conditions: Determinants of Friction

Carbon-based coatings doped by copper: Tribological and mechanical behavior in olive oil lubrication

A Study on Dimethacryloyloxy Alkane Derivatives Having an Anti-wear Performance as Lubricating Oil Additives

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