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A high frequency movement of the substrate is known to affect the forces of friction and adhesion in a number of different ways [1-4]. For hard contacts, the forces of friction typically are reduced by mechanical oscillations. The same is found for the pull-off force of a micron-sized sphere, when detached from the surface of a quartz crystal microbalance (QCM) [5]. We report on an increase of the pull-off force upon oscillating the substrate. Various structured silicone surfaces (kindly provided by Marleen Kamperman, Saarbrücken) were brought into contact with the surface of the QCM. At oscillation amplitudes above 10 nm, the force of detachment increased. Presumably, this increase goes back to a more intimate contact, induced by the motion of the substrate. The formation of the contact is accompanied by relaxation processes inside the soft adherend, which are accelerated by acoustic waves. Temperature plays some role, as well.
[1] Socoliuc, A.; Gnecco, E.; Maier, S.; Pfeiffer, O.; Baratoff, A.; Bennewitz, R.; Meyer, E., Science 2006, 313, 207. [2] Bureau, L.; Baumberger, T.; Caroli, C., Physical Review E 2000, 62, 6810. [3] Dinelli, F.; Biswas, S. K.; Briggs, G. A. D.; Kolosov, O. V., Applied Physics Letters 1997, 71, 1177. [4] Heuberger, M.; Drummond, C.; Israelachvili, J., Journal of Physical Chemistry B 1998, 102, 5038. [5] S. Rudenkiy, PhD thesis, Clausthal University of Technology 2007. |
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