VISCOSITY OF SPONGE PHASE IN POROUS-MEDIUM

Sponge phases are phases of randomly connected membranes. We present an experimental investigation of their rheological properties. Both data on the <<bulk>> viscosity and the effective viscosity through pores are presented. When the bulk viscosity is of the order of a few times the solvent viscosity and is Newtonian in the accessible shear rates (10(-2)-10(2) s-1), the flow of the sponge through cylindrical pores leads to non-Newtonian behaviour. At low shear an enhanced viscosity as the sponge size approaches the pore diameter is observed, while at larger shear rates, the apparent viscosity saturates towards a smaller value close to that measured in the bulk. A simple model based on obstruction and deformation is introduced to describe these different regimes.