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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 30: Friction and Rheology

CPP 30.2: Talk

Tuesday, March 13, 2018, 12:15–12:30, C 264

Measuring lateral force on soft and stiff materials with Intermodulation AFM — •Per-Anders Thorén, Riccardo Borgani, Daniel Forchheimer, and David B. Haviland — Department of Applied Physics, KTH Royal Institute of Technology Stockholm SE-106 91, Sweden

We present a technique [1] for measuring the velocity-dependence of frictional forces on a single asperity (an AFM tip) reaching velocities up to several cm/s. The method is based on the measurement and analysis of intermodulation products, or frequency mixing of multiple drive tones near a high Q torsional resonance, which arise from the nonlinear frictional force. The method gives the oscillation amplitude dependence of both conservative and dissipative dynamic force quadratures, revealing the transition between static and dynamic friction at the nanometer scale. We show measurements on a stiff mica sample and for a few different soft polymer surfaces such as PDMS and a PS-LDPE-blend. Using a modified Prantl-Tomlinson model [1], we simulate the interaction of the cantilever and its tip with the mica-surface. The softer polymer surfaces are discussed in terms of a moving surface model [2], where the finite relaxation time of the lateral deformation of the viscoelastic surface gives rise to the hysteresis seen in the force quadrature curves.

[1]: P-A. Thorén et al., Nat. Commun. 7, doi:10.1038/ncomms13836 (2016)

[2]: P-A. Thorén et al., arXiv http://arxiv.org/abs/1711.09024 (2017)