Mechanochemical Effect of Filler Surface Functionality on Fluoropolymer Tribology

Sun, Wei; Liu, Xiaojun; Song, Qingrui; Liu, Kun; Wang, Wei; Lu, Yunxiang

doi:10.1021/acs.macromol.1c00395

Cited by 28 publications

(5 citation statements)

References 65 publications

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“…In our simulations results of Figure c, six types of tribochemical products and reactions can be observed for the material wear about the degradation of PTFE chains and the removal of atoms from the metal surface, (1) as shown in Figure c,d, Fe 2 O 3 single asperity caused the breakage and degradation of PTFE chains by the pressure and mechanical shear, generating small molecules with free radicals. The broken and shortened chains can be evidenced by FTIR with strong peaks at 1315 and 1360 cm –1 and by XPS analysis with additional peaks between 285 and 289 eV . (2) The carbon dangling bonds reacted with O and Fe of the Fe 2 O 3 , which induced the chemical wear of Fe 2 O 3 (the details can be seen from Section S6 in Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…The broken and shortened chains can be evidenced by FTIR with strong peaks at 1315 and 1360 cm −110 and by XPS analysis with additional peaks between 285 and 289 eV. 58 (2) The carbon dangling bonds reacted with O and Fe of the Fe 2 O 3 , which induced the chemical wear of Fe 2 O 3 (the details can be seen from Section S6 in Supporting Information). ( 3) The exposed reactive iron atoms were worn out and fluorinated to form iron fluorides and C−Fe bonds.…”

Section: Simulation Detailsmentioning

confidence: 99%

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How Polytetrafluoroethylene Lubricates Iron: An Atomistic View by Reactive Molecular Dynamics

Zhang

et al. 2022

ACS Appl. Mater. Interfaces

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The tribochemistry and transfer film formation at the metal/polymer interface plays an essential role in surface protection, wear reduction, and lubrication. Although the topic has been studied for decades, challenges persist in clarifying the nanoscale mechanism and dynamic evolution of tribochemical reactions. To investigate the tribochemistry between iron and polytetrafluoroethylene (PTFE) in ambient and cryogenic environments, we have trained and expanded a ReaxFF reactive force field to describe iron−oxygen−water−PTFE systems (C/H/O/F/Fe). Using ReaxFF molecular dynamics simulations, we find that mechanical shearing of single asperity induced the degradation of PTFE molecules and radicals, showing subsequent oxidation and hydroxylation reactions of the radicals initiated by C−C bond cleavage, in agreement with previous experimental observations. Furthermore, we studied mechanisms of interfacial tribochemical reactions and formation of transfer films. We found that tribochemical wear and Fe−C and Fe−F bonding networks are important mechanisms for anchoring molecular chains to form a transfer film on the iron countersurface. Hydroxyl groups can dehydrogenate to form short and strong chelation bonds with the Fe 2 O 3 countersurface. A friction-induced oriented molecular layer plays a key role in reducing friction, which is responsible for the excellent lubrication property. By varying temperatures in the range of 10−300 K, we found a nonmonotonic change in friction with a maxima at 100 K. At cryogenic temperatures, the molecular mobility was obviously suppressed, while the chain rigidity was enhanced, resulting in the less oriented interface and brittle-like shear interface, which is responsible for nonmonotonic friction. This work elucidates mechanisms of tribochemical reactions and transfer film formation between iron and PTFE at the atomistic level, facilitating design and development of self-lubricating materials, especially under harsh conditions.

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Section: Resultsmentioning

confidence: 99%

Section: Simulation Detailsmentioning

confidence: 99%

How Polytetrafluoroethylene Lubricates Iron: An Atomistic View by Reactive Molecular Dynamics

Zhang

et al. 2022

ACS Appl. Mater. Interfaces

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“…In the presence of water and oxygen, Fig. 13(c), PTFE radicals react with oxygen to form relatively stable peroxy radicals (-OO*), which forms carboxylic acid (-COOH) in presence of water [46,47,62]. The carboxylic acid end groups further react with metal to form carboxylate salt [34,48,61].…”

Section: Mechanistic Discussionmentioning

confidence: 99%

Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)

Johansson,

Marklund,

Björling

et al. 2023

Friction

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Carbon fiber reinforced polytetrafluoroethylene (CF/PTFE) composites are known for their exceptional tribological performance when sliding against steel or cast iron in inert gas environments. Compared to experiments in humid air, about an order of magnitude lower wear rate and several times lower coefficient of friction have been reported for tests conducted in dry nitrogen and hydrogen. Moreover, trace moisture has been shown to affect the friction and wear significantly of this tribosystem, although a possible effect of oxygen cannot be ruled out due to uncertainties regarding the oxygen concentrations. While several studies have pointed out the environmental sensitivity of CF/PTFE, the understanding of the underlying mechanisms are very limited. The objective of this research is to investigate the individual and combined effect of oxygen and moisture on the tribological behavior of CF/PTFE sliding against steel. Additionally, this study aims to elucidate the underlying mechanisms that govern the environmental sensitivity of the system. Climate-controlled three-pin-on-disc experiments were conducted in nitrogen atmospheres at various concentrations of oxygen and moisture. The tribological results clearly demonstrate that both moisture and oxygen contribute to increased friction and wear. However, the adverse effect was much more pronounced for oxygen than moisture. A qualitative method was developed to estimate the tribofilm coverage on the CF/PTFE surface. Results showed strong correlation between high coverage of strongly adhered tribofilm and low wear rate. Moreover, a loosely adhered tribofilm was observed on top of the CF/PTFE surface in presence of moisture. FTIR analysis indicated that the loosely adhered tribofilm found in the moisture-enriched environment contained a significant amount of adsorbed water, which may explain the lower coefficient of friction in presence of moisture compared to oxygen. The adsorbed water in the loosely adhered tribofilm could be an indication of moisture-driven lubrication by the non-graphitic carbon in the tribofilm.

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“…Density functional theory is widely used to study the electronic interactions and chemical reactions between metal surfaces and adsorbed molecules [39]. To explore the differences in polarity and reactivity between base oil and additives, the electrostatic potential distribution and reactive active sites were calculated based on geometric optimization.…”

Section: Density Functional Theory Calculationsmentioning

confidence: 99%

On the Structure–Activity Relationship of Glyceryl oleate Friction Modifiers and Its Synergistic Mechanism on Phosphate ester Antiwear Additives

et al. 2023

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The structure-activity relationship of glyceryl oleate organic friction modi ers and the difference in interaction with antiwear additives signi cantly affect the friction and wear characteristics of the lubrication system. This paper comprehensively considers the differences between polar functional groups and hydrocarbon tail chains, a combination of experiments and simulations were used to investigate the structure-activity relationships of three glyceryl oleate friction modi ers and the synergistic antiwear mechanisms with phosphate ester additives. The results indicate that the reduction of hydroxyl groups in glyceryl oleate weakens the electrostatic interaction with the metal interface and hydrogen bonding interaction, and the increase in hydrocarbon tail chains leads to the enhancement of the steric hindrance effect. Resulting in the substitution of polar functional groups and the increase in hydrocarbon tail chains deteriorating tribological properties. In addition, the binary additive system of glyceryl monooleate and phosphate ester exhibits a signi cant synergistic antiwear effect. It is attributed to the chemisorption of additive O(C = O/P-O/P = O) active sites and the Fe 2 O 3 metal interface, GMO hydrogen bond interactions, the deprotonation of phosphate ester, as well as the carbonate and phosphate protective lm generated by tribochemical reaction.

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Mechanochemical Effect of Filler Surface Functionality on Fluoropolymer Tribology

Cited by 28 publications

References 65 publications

How Polytetrafluoroethylene Lubricates Iron: An Atomistic View by Reactive Molecular Dynamics

How Polytetrafluoroethylene Lubricates Iron: An Atomistic View by Reactive Molecular Dynamics

Mechanisms behind the environmental sensitivity of carbon fiber reinforced polytetrafluoroethylene (PTFE)

On the Structure–Activity Relationship of Glyceryl oleate Friction Modifiers and Its Synergistic Mechanism on Phosphate ester Antiwear Additives

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