Droplet-based microfluidic devices are now more than ever used for the synthesis of nanoparticles with low polydispersity and well-defined properties suitable for various industrial applications. Very small reaction volumes (microlitre to femtolitre) and short diffusion lengths, provide superior mixing efficiency and heat transport. Both play the dominant role in case of ultra-fast chemical reactions triggered upon reactant mixing, e.g. preparation of colloidal silver by reduction of silver salt. The high sensitivity of these systems to process variables makes otherwise more straightforward batch-wise production prone to suffer from inconsistency and poor reproducibility, which has an adverse effect on the reliability of production and further particle utilisation. This work presents a rigorous description of microfluidic droplet formation, reactant mixing, and nanoparticle synthesis using CFD simulations and experimental methods. The reaction mixture inside of droplets was homogenized in less than 40 milliseconds, which has been confirmed by simulations. Silver nanoparticles produced by droplet-based microfluidic chip showed superior to batch-wise preparation in terms of both particle uniformity and polydispersity.
Keywords: CFD simulation; Droplets; Mixing efficiency; Nanoparticles; Two-phase flow.