Structural transitions in crystalline foams
Laboratoire d'Ultrasons et de Dynamique des Fluides Complexes,
URA 851, Université Louis Pasteur, 4 rue Blaise Pascal,
F-67070 Strasbourg Cedex, France
Accepted: 15 January 1998
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.
PACS: 82.70.Rr – Aerosols and foams / 68.90.+g – Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and whiskers / 61.72.-y – Defects and impurities in crystals; microstructure
© EDP Sciences, 1998