Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 87: Focussed Session: Solid-liquid Interfaces III

O 87.2: Talk

Friday, March 15, 2013, 10:45–11:00, H31

Studying confined liquids by using the thermal fluctuations of cantilevers — •Fei Liu, Sissi de Beer, Dirk van de Ende, and Frieder Mugele — MESA+, University if Twente

By analyzing the thermal fluctuations of atomic force microscopy (AFM) cantilevers, we characterize the distance-dependent interaction stiffness and dissipation in bulk/confined octamethylcyclotetrasiloxane (OMCTS), which exhibits short-range ordering (and hence forces) on confinement. In the measurement, the thermal fluctuations of the tip are recorded and parsed into segments as the tip approaches the surface. Each section is transformed to a power spectrum, which we fit to a simple harmonic model. From the fitted resonance frequency and quality factor, we extract the interaction stiffness and damping coefficient. The technique is validated by measuring the bulk viscosity with a blunt tip. Then the experiment is done with sharp tips. It is observed that the interaction stiffness matches well with theory prediction- exponentially decaying oscillatory cosine function w.r.t tip-surface distance. The damping displays non-monotonic behavior and thus deviates from continuum hydrodynamics.