title: Fluidization of granular media wetted by liquid 4He.
abstract: We explore experimentally the fluidization of vertically agitated polymethylmethacrylate spheres wetted by liquid 4He . By controlling the temperature around the lambda point, we change the properties of the wetting liquid from a normal fluid (helium I) to a superfluid (helium II). For wetting by helium I, the critical acceleration for fluidization (Gamma_{c}) shows a steep increase close to the saturation of the vapor pressure in the sample cell. For helium II wetting, Gamma_{c} starts to increase at about 75% saturation, indicating that capillary bridges are enhanced by the superflow of the unsaturated helium film. Above saturation, Gamma_{c} enters a plateau regime where the capillary force between particles is independent of the bridge volume. The plateau value is found to vary with temperature and shows a peak at 2.1K , which we attribute to the influence of the specific heat of liquid helium.
authors.affiliation: Max Planck Institute for Dynamics and Self-Organization, Bunsenstrasse 10, 37073 Göttingen, Germany. kai.huang@ds.mpg.de
authors.forename: K
authors.initials: K
authors.lastname: Huang
authors.forename: M
authors.initials: M
authors.lastname: Sohaili
authors.forename: M
authors.initials: M
authors.lastname: Schröter
authors.forename: S
authors.initials: S
authors.lastname: Herminghaus