Parameter tuning in microfluidic flow-focusing droplet generators for tailored ADN Emulsions

Microfluidic systems enable the formation of highly monodisperse droplets for numerous lab-on-a-chip and chemical synthesis applications while providing a wide range of customizable droplet sizes. This characteristic was used in this work to design the shape of ammonium dinitramide (ADN) droplets or crystals. ADN is a promising green oxidizer that can replace ammonium perchlorate in solid rocket propellants. To achieve high packing density, ADN must be used in the form of spherical crystalline particles with defined particle size. A microfluidic emulsion crystallization process was developed. Diverse droplet formation regimes were identified as a function of capillary number, flow rate ratio as well as geometric parameters, and described in terms of droplet size and droplet size distribution. The result is a guideline to produce desired emulsions with a specific droplet size and a narrow droplet size distribution for the ADN/paraffin system.