| AVS 63rd International Symposium & Exhibition | |
| Tribology Focus Topic | Wednesday Sessions |
| Session TR+AS+NS+SS-WeA |
| Session: | Nanoscale Wear: Applications to Nanometrology and Manufacturing |
| Presenter: | Roland Bennewitz, INM - Leibniz Institute for New Materials, Germany |
| Authors: | R. Bennewitz, INM - Leibniz Institute for New Materials, Germany J. Blass, INM - Leibniz Institute for New Materials BL. Bozna, INM - Leibniz Institute for New Materials M. Albrecht, Saarland University G. Wenz, Saarland University |
| Correspondent: | Click to Email |
Molecular films on surfaces can be used to control friction if it is dominated by adhesive shear rather than surface deformation. The underlying molecular mechanisms can be explored by high-resolution friction force microscopy.
We have developed a molecular toolkit for the control of friction and adhesion by supramolecular interactions in aqueous environments. The contacting surfaces are functionalized by cyclodextrin molecules. The interaction is mediated by ditopic connector molecules with hydrophobic end groups which form inclusion complexes with the cyclodextrin molecules on opposing surfaces. Significant friction and adhesion has been measured in atomic force microscopy experiments for connector molecules with adamantane, ferrocene, and azobenzene end groups.
For adamantane connector molecules, adhesion is found to be strongly dependent on the pulling rate due to a transition from subsequent peeling of individual bonds for slow pulling to multivalency effects at fast pulling. In contrast, friction does not depend on the sliding velocity [1].
The use of azobenzene connector molecules allows for switching of adhesion and friction by light stimuli [2]. Switching of friction by electrochemical stimuli for ferrocene connector molecules is less effective due to molecular interactions which are specific to the connector molecules but do not change with the potential [3]. We will discuss differences in rupture and rebinding dynamics for the three connector molecules and their influence on the rate dependence of adhesion and friction.
Cyclodextrin molecules have also been included in stiff polymers whose end groups are attached to tips or surfaces. The polymer-functionalized surfaces exhibit interesting variations of shearing and peeling mechanisms.
1. Blass, J., et al., Dynamic effects in friction and adhesion through cooperative rupture and formation of supramolecular bonds. Nanoscale, 2015. 7(17): p. 7674-7681.
2. Blass, J., et al., Switching adhesion and friction by light using photosensitive guest-host interactions. Chemical Communications, 2015. 51(10): p. 1830-1833.
3. Bozna, B.L., et al., Friction Mediated by Redox-Active Supramolecular Connector Molecules. Langmuir, 2015. 31(39): p. 10708-10716.