Microfluidic production of chitosan nanoparticles via Ouzo effect

In the present work, chitosan nanoparticles are produced through the Ouzo effect in an X-shaped microreactor configured with three inlets and one outlet. The solvent phase, i.e., an aqueous solution of acetic acid, sodium acetate, and chitosan, enters from the central inlet channel, whereas the antisolvent solution, i.e., an aqueous solution of sodium acetate, flows from the two lateral inlets. We investigate two different chitosan concentrations and the effect of flow rates on the fluid dynamics and particle size distribution. The hydrodynamic flow focusing regime occurs at low flow rates and is characterized by a confined central flow of the solvent phase. As flow rates increase, the flow field exhibits a transition from flow focusing to a vortex regime, marked by the emergence of two pairs of counter-rotating vortices. Notably, this transition tends to shift to higher flow rates with an increase in chitosan concentration. Experimental results, corroborated by numerical simulations, demonstrate that the flow focusing regime produces smaller and monodispersed nanoparticles, whereas the vortex regime yields larger and polydispersed particles, as dimensionally characterized through Dynamic Light Scattering and Field Emission Gun Scanning Electron Microscopy.