Keynote Talk  - Wednesday, 15 September I 9:15 AM (CEST)

Friction is defined as the resistance acting against the motion of two bodies sliding past each other. The situation becomes more complicated in soft materials, biological or biomimetic systems, which usually display complex shapes and elasticities and hence complicate the understanding of friction on a molecular scale. However, it remains still unclear how molecular friction properties affect macroscopic friction properties of those materials. The AFM is a versatile tool for imaging and force spectroscopy at the nanoscopic to mesoscopic scale which we use to understand friction and adhesion properties of molecular systems.

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We use AFM-based force spectroscopy to probe single polymer adhesion and friction at interfaces in liquid environment. To that aim we have developed functionalization protocols for covalent binding of single polymers to AFM cantilever tips. [1] We have used vertical pulling of single polymers to probe the adhesion and mechanics of single polymers on a great variety of solid substrates. [2,3] Then, we have extended our

method towards lateral pulling of single polymers revealing different friction motifs. [4,5]

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Here, we will show how to use angle dependent pulling in order to study the role of single molecular bonds and their multidirectional, velocity dependent on- and off-binding. This will enhance the understanding of the relation between single molecule friction and adhesion and will help to discover the molecular origin of friction.

Furthermore, we will present how different moieties of complex molecules such as

mucin affect the lubrication properties of surfaces.

 

References:

[1] Kolberg et al., J. Vis. Exp., 157, e60934 (2020).

[2] Horinek et al., PNAS, 105(8), 2842–2847 (2008).

[3] Kolberg, et al., J. Am. Chem. Soc., 141 (29), 11603 (2019).

[4] Balzer et al., Angew. Chem. Int. Ed. 52,25, 6541 (2013).

[5] Balzer et al., Soft Materials 12, S106-S114 (2014).

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