Understanding tribochemical reaction mechanisms is necessary to develop a novel resin material that can easily slide on metallic parts. For this purpose, the chemical reaction dynamics between poly(tetrafluoroethylene) (PTFE) resin and an aluminum surface were studied by using a quantum chemical molecular dynamics simulation [Onodera, T., et al. J. Phys. Chem. C 2014, 118, 5390−5396]. The study showed that the PTFE tribochemically reacted with the oxidized surface of aluminum, forming two chemical products, namely, aluminum fluoride and depolymerized PTFE with a carbon double bond at the terminus of the PTFE polymer chain. The carbon backbone was exposed by changing to a double bond configuration, although that in genuine PTFE is fully covered by fluorine atoms. The subsequent chemical reaction of the polymer that reacts with gaseous molecules in the atmosphere (i.e., nitrogen, oxygen, and water vapor) was first studied by density functional theory (DFT). The DFT calculation results show that the chemical reaction of PTFE with water vapor was the most likely to occur and that a carboxyl group was finally formed on the terminus of the PTFE chain. The effect of the chemical reaction with water vapor on formation of a PTFE transfer film on an aluminum surface, which directly affects tribological performance of the focusing system, was then investigated by a classical molecular dynamics method. By forming a carboxyl group as a reaction product with water vapor, the amount of PTFE transfer film on an aluminum fluoride surface (one of the tribochemical reaction products) was increased. On the other hand, less genuine PTFE (without a carboxyl group) was transferred to the aluminum fluoride. This study clarified that the transfer film is formed easily by the reaction of PTFE with atmospheric water vapor, which thereby improves the tribological performance of the PTFE/aluminum lubrication system.
To develop a novel shearing resin material, it is necessary to understand the mechanism of friction-induced chemistry during the friction process. For this purpose, the chemical reaction of the polytetrafluoroethylene (PTFE) resin on an aluminum surface during friction was first focused on and investigated by a quantum chemical molecular dynamics method. From our simulation, an aluminum atom on a native oxide of aluminum surface led to a tribochemical reaction, which included defluorination of PTFE and aluminum fluoride formation. It was inferred that the aluminum surface acted as a catalytic Lewis acid in which the fluorine atom was removed from the PTFE polymer chain. The tribological performance of the investigated system was reduced by the forming of aluminum fluoride since a self-lubrication by PTFE was inhibited by an interfacial electrostatic repulsion. On the basis of our study, it was suggested that the key to increase tribological performance was a chemical reaction between reactive defluorinated PTFE and environmental water vapor to form a novel functional group on the PTFE chain.
To improve the tribological performance of polytetrafluoroethylene (PTFE) resin sliding against a metallic surface, it is important to understand the chemical behavior of PTFE in this sliding system. The tribochemical reaction of PTFE on an aluminum surface has been strenuously studied by a series of computational chemistry methods [Onodera, T., et al. J. Phys. Chem. C 2014, 118, 5390−5396, and Onodera, T., et al. J. Phys. Chem. C 2014, 118, 11820−11826]. One of the most important insights was that PTFE reacted tribochemically with the oxidized surface of aluminum as a Lewis acid catalyst, forming a fluoride on the aluminum surface. The aluminum fluoride formed was a cause of decreasing tribological performance of PTFE because of less formation of a transfer film. In regard to this tribochemical reaction, it was suggested that preventing the fluoride formation is a key to improving the tribological performance of PTFE sliding against an aluminum surface. In this study, to investigate fluoride formation by a tribochemical reaction, the catalytic effect of an oxidized aluminum surface was investigated experimentally and theoretically. Two phases of an oxidized aluminum surface, namely, the α and γ phases of alumina, were chosen for investigating the catalytic tribochemistry of PTFE. A thermogravimetric analysis showed that the γ-alumina surface potentially exhibited a stronger catalytic effect in regard to PTFE since the reaction took place at lower temperature. The effect of the catalytic reaction on the tribological performance of PTFE was then investigated by a pin-on-disk tribometer. The results of this investigation show that the amount of wear of PTFE on the γ-alumina surface was higher than that on the α-alumina surface. By observing the wear scar on alumina surfaces by a scanning electron microscope (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), it was clarified that the transfer film formed on the γ-alumina surface was less abundant, while it was regularly formed and more abundant on the α-alumina surface. In other words, the antiwear performance of PTFE was decreased because a lower amount of transfer film was formed by the catalytic effect during friction. In addition, a density-functional-theory (DFT) calculation also showed a stronger catalytic effect on the γ-alumina surface because the energy barrier for the chemical reaction producing fluoride was lower than that on the α-alumina surface. On the basis of these results, it was suggested that controlling the catalytic reaction of PTFE on the sliding surface is one of the ways to improve the antiwear performance of PTFE.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.