Flow of microemulsions through microscopic pores

The flow of the microemulsion dioctylsulfosuccinate (AOT)/decane/water through 0.1 and 1.0 μm diameter pores was studied for water droplet volume fractions ranging from 0 to 0.5. The viscosity of these microemulsions, as measured in a capillary viscometer with a bore of ≊1 mm diameter, exceeds by as much as a factor of 4 theoretical predictions of the viscosity of suspensions of hard or liquid spheres. If droplet clustering causes this viscosity enhancement, then flow of the microemulsions through pores with diameter small compared to the characteristic cluster size should display a large finite-size effect. The apparent viscosity of the microemulsions in pores differed from the viscosity measured in the capillary viscometer by less than 40% for 0.1 μm diameter pores and by less than 8% for 1.0 μm diameter pores. These differences are of the same scale as estimates of two effects: adsorption of droplets on the pore wall and the enhanced flow of suspensions near a wall. The absence of larger finite-size effects implies that clustering of droplets on length scales of 0.1 μm or larger does not contribute substantially to the microemulsion viscosity.