# Transitions de Phase de l'Hélium dans les aérogels de silice

Abstract : This experimental work is a contribution to the study of two critical phenomena of helium confined in silica aerogels. With the aim to detect possible changes of the universality class of the liquid-gas critical point for helium adsorbed in aerogels, we have developed an original device, consisting of a simple pendulum, the mass of which is due to both the aerogel and the adsorbed helium. This set-up was validated by measuring the onset of superfluidity within seven different samples. We reproduce known results concerning the change of critical exponent, and give further information on the link between the fractal dimensionality of the sample and the $\zeta$ exponent of the superfluid density. The pendulum was then used to investigate the condensation of helium in aerogels, in the vicinity of the bulk critical point. Our results largely contradict previously published results on the same system : The system is not completely filled with liquid at the saturation pressure. At lower pressure, no well defined first order transition is observed. A sharp but gradual rise in the helium density is however observed . These results are very similar to those observed in more conventional porous media, and can be interpreted as capillary condensation. Finaly, very long time constants are observed in the region of capillary condensation. This type of slow dynamic is expected theoretically and is related to the displacement of a 2D interface in a disordered medium.
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https://tel.archives-ouvertes.fr/tel-00001788
Contributor : Pierre-Etienne Wolf <>
Submitted on : Tuesday, October 8, 2002 - 9:12:10 AM
Last modification on : Friday, December 18, 2020 - 1:34:03 PM
Long-term archiving on: : Friday, April 2, 2010 - 6:29:23 PM

### Identifiers

• HAL Id : tel-00001788, version 1

### Citation

Claude Gabay. Transitions de Phase de l'Hélium dans les aérogels de silice. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Joseph-Fourier - Grenoble I, 2001. Français. ⟨tel-00001788⟩

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