EPL

DOI: 10.1209/epl/i1998-00193-6

Europhys. Lett, 41 (5), pp. 571-576 (1998)

Structural transitions in crystalline foams

P. Boltenhagen and N. Pittet

Laboratoire d'Ultrasons et de Dynamique des Fluides Complexes, URA 851 Université Louis Pasteur - 4 rue Blaise Pascal, F-67070 Strasbourg Cedex, France

(received 2 April 1997; accepted in final form 15 January 1998)

PACS. 82.70Rr - Aerosols and foams.
PACS. 68.90 ${\rm +g}$ - Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and whiskers.
PACS. 61.72 ${\rm -y}$ - Defects and impurities in crystals; microstructure.

Abstract:

In this letter, the structural stability of foam is investigated experimentally. We use crystalline foams (equi-sized gas bubbles confined in a cylindrical glass tube) under conditions of a steady-state drainage where soap solution is added onto the top of the foam at a constant rate. By varying this flow rate, we observe: 1) Reproducible structural transitions that are induced when drainage exceeds a critical liquid flow rate. The transition leads to a new ordered foam stable under the flow. A structural diagram is defined, showing the boundary between the two structures for the whole range of existence of the initial structure. 2) A deviation from the classical Poiseuille behavior of the draining liquid, exhibited at low flow rates, is observed. 3) We propose a simple model for the flow into the foam, explaining both the deviation from the Poiseuille behavior and the stability boundary shown in the structural diagram.

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