One-step generation and characterisation of aerated emulsions using laser diffraction

Dispersions of bubbles and drops in water are widely encountered in many fields, from food industry to cosmetics and oil recovery. Their generation typically requires two steps: either the emulsion is generated first and then aerated, or an emulsion and a foam are generated separately and then mixed. While a variety of techniques to characterise single dispersions of oil or gas exist, the characterisation of composite systems is usually more tricky. In this work, we show that aerated emulsions can be generated by mixing the oil, gas and aqueous phases all together in one step using the double-syringe technique, without the need of two separate processes. We show that such one-step generation ensures a good scale separation between bubbles and drops, with a size ratio in first approximation constant over a very wide range of oil and gas volume fractions. Furthermore, we show that laser diffraction granulometry, so far used to measure only bubbles or drops separately, can be used to rapidly assess the bubble size in these composite dispersions for bubbles up to 100 mu m in diameter. We show that the results are in excellent agreement with a well-established direct technique to measure bubble size in foams as optical microscopy, and we explore the main limits within which the light scattering measurements are robust.