Viscosity effects in foam drainage:
Newtonian and non-newtonian foaming fluids |
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Authors: | M Safouane A Saint-Jalmes V Bergeron D Langevin |
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Institution: | (1) Laboratoire de Physique des Solides, Université Paris-Sud, 91405 Orsay, France;(2) Laboratoire de Physique, ENS Lyon, 69364 Lyon, France |
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Abstract: | We have studied the drainage of foams made from Newtonian and non-Newtonian
solutions of different viscosities. Forced-drainage experiments first show
that the behavior of Newtonian solutions and of shear-thinning ones (foaming
solutions containing either Carbopol or Xanthan) are identical, provided one
considers the actual viscosity corresponding to the shear rate found inside
the foam. Second, for these fluids, a drainage regime transition occurs as
the bulk viscosity is increased, illustrating a coupling between surface and
bulk flow in the channels between bubbles. The properties of this transition
appear different from the ones observed in previous works in which the
interfacial viscoelasticity was varied. Finally, we show that foams made of
solutions containing long flexible PolyEthylene Oxide (PEO) molecules
counter-intuitively drain faster than foams made with Newtonian solutions of
the same viscosity. Complementary experiments made with fluids having all
the same viscosity but different responses to elongational stresses
(PEO-based Boger fluids) suggest an important role of the elastic properties
of the PEO solutions on the faster drainage. |
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Keywords: | 82 70 Rr Aerosols and foams 47 60 +i Flows in ducts channels nozzles and conduits 47 56 +r Flows through porous media |
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