Rational Design of Droplet Microfluidic Reactors for Controllable Non-Newton Viscous Production of Functional Chitosan Microspheres

The uniformity and monodispersity of the chitosan microsphere are essential requirements for its related applications, and the appearance of undesired satellite droplets needs to be avoided. However, preparing monodispersed, uniform, and size-controllable chitosan microspheres is still a significant challenge. In this paper, a droplet-based microfluidic strategy is developed for the chitosan and fluorescent chitosan microsphere synthesis with controllable size and monodispersity. A water-in-oil droplet microfluidic reaction system is formed, and the monodispersed viscous droplet generation one by one in a step T-junction microchannel and solidified microspheres is observed via a chemical cross-reaction. A side microchannel is designed to separate satellite droplets successfully and improve the quality of the product. The effects of flow rates of two phases, phase ratio, and reaction time are investigated experimentally. The stable operating range for viscous droplets is given. The size of the chitosan could be tuned from 50 to 200 μm, and the production rate could reach up to 1.2 mL·h^-1. This work not only provides valuable guidance for polymer microsphere synthesis but also helps to understand the microdispersion mechanism of the non-Newton viscous fluid in depth.