Catastrophic phase inversion in mayonnaise Taylor-Couette turbulence*

Emulsions are commonly found in nature and heavily used in industry. While the properties of the individual fluids are known, the mixture of the two immiscibles can show very non-intuitive properties, especially at high Reynolds numbers. In this experimental study, we vary the oil volume fraction of a oil-water emulsion in a Taylor-Couette geometry at typical Reynolds numbers of 10⁶ and measure the torque required to keep the inner cylinder rotating at a constant velocity. When an oil is used with a viscosity larger than water, the apparent viscosity of the emulsions can be described by a laminar model. For an oil which has a viscosity similar to that of water, we witness a catastrophic phase inversion: when the fluid changes from oil droplets in water to water droplets in oil (or vice- versa), the flow morphology changes dramatically, resulting in an almost instantaneous jump in drag.