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Reducing friction and wear is one of the most important requirements for improving the performances of components in many technological devices.
In many cases, especially in aerospace, high-temperature, and computer applications, it is impractical or undesirable to have a liquid lubricant present, and one has to rely entirely on the tribological properties of dry surfaces.
Therefore the functionalization of metallic surfaces with organic molecules to impart "lubricating" properties becomes a subject of major interest both from fundamental and technological point of view.
We compare here two families of organic polymer thin films electrochemically grafted on metal surfaces to elucidate the effect of the polymer main-chain chemical bond structure on tribological properties.
The first family is formed by polymethacrylates bringing different fluorinated lateral groups. These films can be electrografted by the reduction of corresponding monomers in anhydrous solvents to give adherent thin films on the electrode surface.
The second family is constituted by aromatic diazoniums salts that are also known to form thin films on surface electrode under reduction at low cathodic potentials. We studied two new fluorinated diazonium salts.
The physical-chemical films characterizations were made by XPS and ATR FT-IR spectroscopy.
The tribological behaviour of the films was tested in a ball-plane configuration, under reciprocating wear. The organic films were grafted on plane gold coated bronze substrates. The stamped ball was constituted of the same material. We measured at the same time the friction coefficient and the electrical resistance between the ball and the plane.
While the two film families have similar thicknesses and surface energies the tribological and wear properties are radically different. The fluorinated polymethacrylates, having a flexible sp3 bonded main chain chemical structure, show much better properties with respect to diazoniums salts films that have a more rigid sp2 main chain.
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