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IRTG / Soft Matter Science
Stefan-Meier-Str. 21
79104 Freiburg, Germany

+49 761 203 678 34
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You are here: Home Events Prof. Roland Bennewitz "Friction, molecular adhesion, reversible bonds, and multivalency"

Prof. Roland Bennewitz "Friction, molecular adhesion, reversible bonds, and multivalency"

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INM – Leibniz Institute for New Materials, Saarbrücken, Germany

What
  • Seminar
When May 09, 2018
from 02:15 PM to 03:00 PM
Where Seminarraum A, FMF, Stefan-Meier-Str. 21, Freiburg
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The sliding of a contact requires the breaking of bonds, but also leads to formation of new bonds. Is the energy require to break the bonds all dissipated? Friction force microscopy experiments provide insights into the molecular mechanisms of friction for contacts with a small number of bonds. I will discuss results for friction and adhesion where the tip-sample interaction is controlled by supramolecular guest-host bonds. We show that the force required to break single reversible bonds depends on the cantilever stiffness but not on the molecular linker stiffness [1].

For low sliding velocities, the bonds are in thermodynamic equilibrium, i.e. the bonds unbind and rebind many times before the contact moves by one molecular distance on the surface. In this situation, one expects zero friction. Zero friction is indeed observed for a stiff attachment of molecules to tip and surface, but finite friction is observed even at low velocities if the molecular attachment is compliant [2]. The results are discussed in terms of multivalency by comparison with forces measured in pull-off experiments [3]. Molecular simulations clarify the picture of adhesion and friction mechanisms [4]. Finally, we discuss the role of contact aging in the understanding of molecular friction.

[1]    J. Blass, M. Albrecht, G. Wenz, Y. N. Zang, and R. Bennewitz, Physical Chemistry Chemical Physics 19 (2017) 5239.
[2]    J. Blass, M. Albrecht, G. Wenz, R. Guerra, M. Urbakh, and R. Bennewitz, Journal of Physical Chemistry C 121 (2017) 15888.
[3]    J. Blass, M. Albrecht, B. L. Bozna, G. Wenz, and R. Bennewitz, Nanoscale 7 (2015) 7674.
[4]    R. Guerra, A. Benassi, A. Vanossi, M. Ma, and M. Urbakh, Physical Chemistry Chemical Physics 18 (2016) 9248.

invited by Prof. Thorsten Hugel

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