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Communication Dans Un Congrès Année : 2010

New experimental results on foam acoustics

Résumé

We report a set of new experimental results on the acoustic properties of aqueous foams. Many issues are still pending on foam acoustics; it is still not well understood how sound propagates and is attenuated inside foam, and how the acoustic properties depend on the bubble size and liquid fraction. Experimentally, problems often arise from the coupling between such acoustic measurements and the foam aging, which irreversibly modifies both the bubble size and the liquid fraction (also creating vertical gradients of these parameters). First, we present new measurements of sound velocity and sound attenuation (in the ultrasonic frequency range) on various types of controlled foams, and in particular on foams doped with clay particles in order to obtain a coarsening, but not draining, foam. This allows us to study accurately the dependence of the sound features with the bubble and sample sizes and the liquid fraction. In particular, we observe a non-monotonic behavior for the attenuation as foam ages, strikingly reminiscent of results found for bubbly liquids. Secondly, we have studied how a sound wave (emitted by an external speaker) induces bubble displacement. We show that it is possible to detect - by a light scattering technique (Diffusive Wave Spectroscopy) - the tiny acoustic-induced motion of the bubbles. Comparisons between theory and experiments allow us to elucidate the non-trivial acoustic displacement profile inside the foam; in particular, we find that the acoustic wave creates a localized shear in the vicinity of the solid walls holding the foam, in agreement with novel predictions on foam mechanical behaviour at high frequency.
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Dates et versions

hal-01003067 , version 1 (09-06-2014)

Identifiants

  • HAL Id : hal-01003067 , version 1

Citer

Reine-Marie Guillermic, Marion Erpelding, Imen Ben Salem, Benjamin Dollet, Jérôme Crassous, et al.. New experimental results on foam acoustics. International soft matter conference (ISMC2010), Jul 2010, grenade, Spain. ⟨hal-01003067⟩
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