Mixing efficiency affects the morphology and compactness of chitosan/tripolyphosphate nanoparticles

Due to the rapid reaction kinetics, the morphology of chitosan/tripolyphosphate nanoparticles was difficult to control. We mixed chitosan and tripolyphosphate through a multi-inlet vortex mixer at different mixing efficiency and characteristic mixing time (τ_mix). Below a critical τ_mix, the aggregation of primary chitosan/TPP particles can be ceased. The corresponding aggregation time of primary particles (τ_agg) was dependent on the ionic strength, the degree of deacetylation and molecular weight of chitosan. Moreover, the particle compactness was estimated from the hydrodynamic diameter and the turbidity using a model based on the Mie theory. Slow and nonhomogeneous mixing led to more compact nanoparticles, while rapid and homogeneous mixing produced nanoparticles with a higher swelling ratio. Besides, the ionic strength and polymer concentration could affect the internal structure of nanoparticles. This study revealed the significance of mixing on the internal structure of chitosan/TPP nanoparticles, which could guide the preparation of other ionically-crosslinked polysaccharide colloids.