Watergel in Superfluid He-II

The formation of the semitransparent water “clouds” below the surface of superfluid He-II cooled down to 1.3 K, which transform with time to more dense “icebergs” suspended in the bulk of the experimental cell, had been observed for the first time. The water condensate was created by introducing gaseous 4He with the water vapor contamination into the cell filled with He-II. With lowering the level of He-II below the upper edge of an iceberg it could jump down the liquid due to throwing out the cold He gas from its surface. Decomposition of “dry” icebergs with initial dimensions of a few mm, which were collected at the bottom of the cell empty from He-II, on heating above 2.2 K in He gas atmosphere had resulted in a multiple (more than two orders of magnitude) decrease of their volume. So, the total content of H2O molecules in the bulk of the icebergs was less than 1020 cm−3. It can be suggested that the icebergs are composed of small water clusters with mean diameters of about 5 nm covered by a layer of solidified He, which are created in dense He vapor above the liquid. The interaction between the particles penetrated into He-II can lead to the formation of a highly porous matter (watergel) saturated with superfluid helium.