Dynamics of capillary condensation of liquid 4He in various density silica aerogels was investigated systematically. Interfaces were clearly visible when bulk liquid was rapidly sucked into the aerogel. Time evolution of the interface positions was consistent with the Washburn model and their effective pore radii were obtained. Condensation was a single step in a dense aerogel and two steps in a low density aerogel. Crossover between the two types of condensation was observed in an intermediate density aerogel. Variety of the dynamics may be the manifestation of the fractal nature of aerogels which had a wide range of distribution of pore radii.

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Superfluid bubbles in a 4He quantum crystal, which we refer to as quantum negative crystals, were investigated in bcc and hcp phases by visualizing their forms and motions at various temperatures. They were nearly spherical in bcc phase and faceted on the c-plane in their upper part in hcp phase. They steadily rose in the crystal due to gravity. Their direction was vertical in bcc phase and obliquely parallel to the c-facet in hcp phase. We also observed a slowing down of negative crystal in hcp phase caused by the appearance of the a-facet when temperature was lowered. Dynamics and morphology became successively anisotropic with cooling. The driving force by gravity for this motion was derived in the spherical case. Growth coefficient obtained by this model agreed well with the reported values.

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