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Adam A. Feiler*, Lennart Bergström, and Mark W. Rutland. Division of Surface Chemistry, School of Chemical Science and Engineering, Royal Institute of Technology SE-100 44 Stockholm Sweden and *YKI, Institute for Surface Chemistry, 11428 Stockholm Sweden adam.feiler@surfchem.kth.se Typical lubricants reduce friction and wear by physical separation of asperity contacts. In solution, surfactants and polyelectrolytes offer good potential as friction modifiers; yielding short range repulsive forces between surfaces due to steric and or repulsive osmotic forces. However under high loads these surface layers ultimately compress or are removed and the surfaces come into intimate contact. As an alternative approach to reducing friction, we show that repulsive van der Waals forces can prevent contact altogether and friction is essentially precluded and super sliding is achieved. Friction force measurements using colloid probe atomic force microscopy have been conducted to investigate superlubrication between surfaces interacting with repulsive van der waals force. The friction coefficient associated with this system is on the order of 0.0003. This work clearly shows that two surfaces experiencing a repulsive surface force, which diverges at small separations, can slide essentially without friction. The number of systems in which repulsive van der Waals forces could occur is limited but includes metal bearings in a PTFE housing with organic lubricant and certain combinations of technically interesting ceramic materials. References: Feiler A. A., Bergström, L; Rutland M. W. Superlubricity Using Repulsive van der Waals Forces Langmuir, 24 (6), 2274 -2276, 2008. |
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