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Onset of frictional slip by domain nucleation in adsorbed monolayers.

ABSTRACT: It has been known for centuries that a body in contact with a substrate will start to slide when the lateral force exceeds the static friction force. Yet the microscopic mechanisms ruling the crossover from static to dynamic friction are still the object of active research. Here, we analyze the onset of slip of a xenon (Xe) monolayer sliding on a copper (Cu) substrate. We consider thermal-activated creep under a small external lateral force, and observe that slip proceeds by the nucleation and growth of domains in the commensurate interface between the film and the substrate. We measure the activation energy for the nucleation process considering its dependence on the external force, the substrate corrugation, and particle interactions in the film. To understand the results, we use the classical theory of nucleation and compute analytically the activation energy which turns out to be in excellent agreement with numerical results. We discuss the relevance of our results to understand experiments on the sliding of adsorbed monolayers.

SUBMITTER: Reguzzoni M

PROVIDER: S-EPMC2824350 | biostudies-other | 2010 Jan

REPOSITORIES: biostudies-other

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Onset of frictional slip by domain nucleation in adsorbed monolayers.

Reguzzoni Marco M Ferrario Mauro M Zapperi Stefano S Righi Maria Clelia MC

Proceedings of the National Academy of Sciences of the United States of America 20091224 4

It has been known for centuries that a body in contact with a substrate will start to slide when the lateral force exceeds the static friction force. Yet the microscopic mechanisms ruling the crossover from static to dynamic friction are still the object of active research. Here, we analyze the onset of slip of a xenon (Xe) monolayer sliding on a copper (Cu) substrate. We consider thermal-activated creep under a small external lateral force, and observe that slip proceeds by the nucleation and g ...[more]

PMID: 20080546

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Project description:The perception of fine texture of an object is influenced by its microscopic topography and surface chemistry-i.e., the topmost layer of atoms and molecules responsible for its surface energy, adhesion, and friction generated when probed by a fingertip. Recently, it has been shown that human subjects can discriminate high-energy (i.e., hydrophilic), oxidized silicon from low-energy (i.e., hydrophobic), fluorinated alkylsilane-coated silicon. The basis of discrimination was consistent with differences between stick-slip friction frequencies generated when sliding the fingertip across the two surfaces. One aspect that was not examined was the presence of surface relief structures on the fingertip. Indeed, papillary ridges-fingerprints-may be involved in enhanced discrimination of fine textures arising from surface roughness, but how (or whether) fingerprints may also be involved in the discrimination of surface chemistry-through its effect on friction-is unknown. Here, using a mock finger made from a slab of silicone rubber shows that relief structures amplify differences in stick-slip friction when slid across either a hydrophilic oxide or a hydrophobic monolayer on silicon. We quantify the similarity between the friction traces of the mock fingers sliding across hydrophilic and hydrophobic surfaces under varying velocities and applied masses using a cross-correlation analysis. We then convert the cross-correlational data into convenient "discriminability matrices." These matrices identify combinations of downward forces and sliding velocities that enhance differences in friction between hydrophilic and hydrophobic monolayers. In addition, a computational model of macroscopic, "rate-and-state" friction confirms that frictional differences in chemistry are amplified when elastic slabs bear a patterned interface. This biomimetic approach to engineering sliding interfaces may inform the development of improved electronic skin and haptic devices and may contribute to understanding the role of relief structure in tactile perception.

Dataset Information

Onset of frictional slip by domain nucleation in adsorbed monolayers.

Publications

Onset of frictional slip by domain nucleation in adsorbed monolayers.

Similar Datasets

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