Europhys. Lett, 48 (1), pp. 93-98 (1999)
Rheological memory effect in aqueous foam
R. Höhler, S. Cohen-Addad and A. Asnacios
Université de Marne-la-Vallée, Laboratoire de Physique des Matériaux Divisés
et Interfaces - 5 Boulevard Descartes, F-77454 Marne-la-Vallée Cedex, France
(received 13 April 1999; accepted in final form 26 July 1999)
PACS. 82.70Rr - Aerosols and foams.
PACS. 83.70Hq - Heterogeneous liquids: suspensions, dispersions, emulsions, pastes, slurries, foams, block copolymers, etc.
PACS. 83.50By - Transient deformation and flow, time-dependent properties: start-up, stress relaxation, creep, recovery, etc.
We have measured the complex shear modulus G* of aqueous foam before and after applying a strain of the order of the yield strain for a brief period of time. After such a mechanical perturbation we observe transient "strain softening'': the real part of G* is smaller than before and as the foam aging process goes on, it slowly relaxes towards the values obtained for quiescent foam. The characteristic time scale of this relaxation increases with the foam age at which the perturbation is applied, following a scaling law.
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