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.