Owing to its high
resolution, interferometry is a powerful tool for
studying wetting problems at small contact
angles. Using interferometry in 3He/4He
mixtures, we have discovered that in an experimental
cell containing a thin layer of the phase-separated
mixture, the upper 3He-rich
phase is not able to wet the surface of the 4He-rich liquid below in the presence of a
small, continuous feed of 4He atoms to the vapor phase [PRL73,
1388 (1994)]. This finding is quite surprising
since the surface of the 4He-rich phase is covered by an adsorbed layer
of 3He atoms which
should favor spreading of the 3He-rich liquid.
FIGURE Interferogram of phase separated 15% mixture film at T = 0.32 K. The stripe-like feature in the middle of the picture is identified as a floating pool of 3He-rich phase on top of the lower 4He-rich superfluid. The lower frame displays a reconstructed surface profile from left to right over the stripe; the angle formed between the rising 3He surface with respect to the flat 4He-rich phase level is marked. Both bright and dark fringes were employed in the analysis.