Regensburg 1998 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 14: Quantenflüssigkeiten (Experiment)
TT 14.4: Vortrag
Mittwoch, 25. März 1998, 15:45–16:00, H 19
The role of the thin film on the nonwetting behaviour of the 4He–Cs system
— •Jürgen Klier1,2, Adrian Wyatt1, and Paul Leiderer2 — 1Department of Physics, University of Exeter, Exeter, EX4 4QL, UK — 2Universität Konstanz, Fakultät für Physik, Postfach 5560 M675, D–78434 Konstanz
In general it is observed that liquid 4He does not wet Cs below a certain wetting temperature, TW. However, there exist a variety of different results of 4He on Cs. Although TW does not vary very much there are considerable differences in the hysteresis and absolute values of the contact angle on the various Cs surfaces that have been studied. We will present ideas, which allow to understand the observed discrepancies between these experiments. Most striking are the differences in temperature dependence of the surface free energies deduced from the observed contact angles. The range goes from no temperature dependence up to a very strong one, even the gradient of these dependencies can change its sign. These effects should be due to different surface structures and/or contaminations of the Cs. We argue that this surface morphology influences the thin film state, which can be either a 2D–gas or a 2D–liquid, and the solid/liquid interface and excitations. These in turn determine the surface free energies and hence change the wetting behaviour. This leads to a qualitative and general understanding of the wide ranging results to date.