Electrokinetic behavoir of chitosan adsorbed on o/w nanoemulsion droplets

Abstract

Chitosans with different molecular weight and degree of acetylation (DA) were adsorbed onto lecithin stabilized nanoemulsion droplets at pH ∼4.7. The electrokinetic properties of the nanoemulsion were investigated by using dynamic light scattering. According to the experimental data, the isoelectric point (IEP) of the droplets in the suspension at the presence of oppositely charged chitosan, does not depend on the polyelectrolyte molecular weight (when DA of chitosan is lower than 32%). Due to the high charge density of these polymer chains and low surface charge density of the lecithin stabilized droplets, the chitosan molecules retain part of the condensed counterions upon the adsorption process. Thus, the registered electrophoretic mobility corresponding to the “effective”, and not “real”, the electrokinetic charge of the droplets covered by a polymer layer. The stability behavior of the nanoemulsion in the presence of chitosan with lower charge density is different, and the IEP and stabilization of the system are achieved at higher polymer concentration. The coincidence in the polyelectrolyte concentration corresponding to IEP and minimum stability of the nanoemulsion against coagulation agrees with the notion that the electrostatic interactions are predominant in the coating layer formation. In spite of the similar electrokinetic behavior of the droplets covered with chitosan with low DA and different molecular weight, the polymers have different biological activity which might be results from different charge density of the molecules. In the present study, we show that the electrical polarizability is a complex parameter that can allow to more detailed characterization of the electrical properties of the chitosan.