Kinetics of coacervation transition versus nanoparticle formation in chitosan–sodium tripolyphosphate solutions

Chitosan (deacetylation = 75–85%) and sodium tripolyphosphate (TPP) solutions were observed to undergo spontaneous coacervation transition or nanoparticle formation depending on the chitosan concentration and the volumetric mixing ratio [chitosan/TPP]. Three distinct conditions have been identified: (i) [chitosan] ≤ 0.5 mg/ml, 0.5 ≤ [chitosan/TPP] ≤ 2 and pH < 5.5, yields spontaneous coacervation, (ii) 0.5 ≤ [chitosan] ≤ 2.5 mg/ml, [chitosan/TPP] ≥ 2 and 3.5 < pH < 5.5, produces chitosan nanoparticles and (iii) 0.5 ≤ [chitosan] ≤3 mg/ml, 3 ≤ [chitosan/TPP] ≤ 6 and 5