Institute of Physical Chemistry > Research > High-frequency contact mechanics using QCM

High-frequency contact mechanics using QCM

The quartz crystal microbalance is typically used to study thin films and planar adsorbates from the liquid phase.  When the resonator plate is in contact with discrete point-contacts (Fig. 1), its response is much different from the response to loading with layered samples.  Firstly, the resonance frequency increases.  Also, there is a stress concentration at the point of contact, giving rise to nonlinear force-displacement relations.  These are easily evidenced from a dependence of the resonance frequency on the amplitude of oscillation.1  Some of the results obtained so far can be understood as a gradual transition from stick to slip.

Current DFG-funded research is concerned with more detailed studies of this transition.  Topics of the research are:

  • The study of third-harmonic generation2, quantifying nonlinear behavior on the nanosecond time-scale.
  • The study of stick and slip on the microsecond timescale, employing intermodulation spectroscopy3.
  • Identification of different mechanisms leading to nonlinear behavior (partial slip, heat, wear, rolling friction/sliding friction).
  • The search for shake-down, meaning a decrease of dissipation with time under oscillatory frictional loading4.
  • Turning these insights into a methodology to study soft layers (Fig. 1).
Fig. 1: If a soft film is loaded with a sphere from the other side, it becomes a lubricant. Secondarily a point contact is created. The tribological properties of the film give information on its structure and functionality.

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