Colloid fabrication by co-extrusion

We propose a novel technique that allows assembling composite particles by manipulating three (initially fluid) phases, e.g. gas bubbles or liquid droplets (phase 1) in one liquid (phase 3), coated by another one (phase 2). In this way, we can control (i) the type of disperse phase fluid and its flow rate, (ii) the type of the coating material, its composition, and its flow rate, and (iii) the type of the continuous phase and its composition. All this gives us numerous opportunities to prepare new disperse systems with interesting applications. We describe two sets of experiments. In the first one we produce gas bubbles coated with oil. In the second one we produce stable foam that is stabilized by a surfactant formed in situ on the surface of each separate bubble. The surfactant is formed by a chemical reaction between a fatty acid solution spread on the bubble surface and an aqueous solution of NaOH as a continuous phase. The foam grows linearly with time during the supply of the fatty acid solution. When we stop the supply of the fatty acid the foam growth stops. The simple examples show that with carefully chosen phases and precise control of the experimental conditions we can produce a whole range of different colloids: composite capsules, shell particles or fluid dispersions, etc.