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CPP: Chemische Physik und Polymerphysik

CPP 13: POSTER New Experimental Techniques

CPP 13.1: Poster

Dienstag, 28. März 2006, 17:00–19:00, P3

Measurements of interfacial viscoelasticity with the quartz crystal microbalance: influence of acoustic scattering from a small crystal-sample contact — •Alexander Martin König, Mathis Düwel, Binyang Du, Miriam Kunze, and Diethelm Johannsmann — Institute of Physical Chemistry, Clausthal University of Technology,Arnold-Sommerfeld-Str. 4, D-38678 Clausthal-Zellerfeld

We discuss the influence of the limited contact size on measurements of high-frequency interfacial viscoelasticity performed with a combination of the quartz crystal microbalance (QCM) and the Johnson-Kendall-Roberts (JKR) apparatus. In this instrument, a sphere-plate contact is established between an elastomeric lens and a quartz resonator. The analysis is carried out in the frame of the sheet-contact model, which states that the shift of resonance frequency and bandwidth both are proportional to the contact area as long as the contact area is much smaller than the crystal itself. In particular, the ratio of the shift in bandwidth and the shift in frequency (termed D-f ratio) is predicted to be constant and independent of geometry. However, the experiment does show a slight increase of the D-f ratio with contact radius when the contact radius is comparable to the wavelength of sound inside the crystal. This effect can be explained by acoustic scattering.