Effective viscosity measurement of interfacial bubble and particle layers at high volume fraction

• A new concept for measuring the viscosity of bubbly liquid that has a high void fraction, close to the packing limit has been suggested and applied.
• Effective viscosity of bubbly liquid in three different classes of bubble size from, microbubble to large bubbles has been obtained, which are much larger than those, measured in dilute situations.
• The viscosity of a thin layer consisted of solid particles has been also measured, which, has shown intrinsic flow curve that is provided by shear localization events.

An experimental method for measuring the effective viscosity of two dimensional dispersion systems is proposed. The method is based on interfacial rheology, which was originally developed to investigate surface active adsorption layers such as protein film formed at liquid–liquid interfaces. Bubbles or rigid particles at around 50% of volume fraction in liquid are positioned in the gap between a rotating disk and a stationary cylindrical container. With this configuration, shear-rate dependent effective viscosities of bubble and particle layers were investigated. Steep shear-thinning property is observed for spherical bubble systems in the shear rate regime from 10−1 to 102 s−1. This is explained by topological transition from regular to random arrangement of the bubbles at the interface. For rigid particle systems, the viscosity starts from high value due to solid contact friction, then decreases sharply due to fluidization process until inter-particle collision lead to an increase of the viscosity.