CHITOSAN-BEHENIC ACID MONOLAYER INTERACTION AT THE AIR-WATER INTERFACE: CHARACTERIZATION OF THE ADSORBED POLYMER LAYERS BY X-RAY REFLECTIVITY

The aim of this research was to investigate the adsorption of chitosan, a pseudo-natural polyelectrolyte, with an oppositely charged surface consisting of a surfactant monolayer (behenic acid) at the air-water interface. The structure of the adsorbed layers and the effect of the net charge of the polymeric chains on the arrangement of the surfactant molecules in the monolayer were determined by a surface-sensitive technique: X-ray reflectivity (XRR). Our purpose was to study a model system in order to explain the adsorption mechanism and the conformation of the adsorbed polyelectrolyte on the oppositely charged surface of a lipidic vesicle. The interfacial complex layer stabilizes the particles and protects their integrity against different stresses (pH, ionic concentration, osmotic shock, etc.). These systems may be used in many applications, such as the fabrication of composite nanoparticles suitable for delivery and/or storage of drugs. Objects like micelles and nano-or microvesicles or capsules decorated with natural and biocompatible polyelectrolytes adsorbed at the interface may have a controlled net charge by tuning the physicochemical parameters, pH, and concentration and the structure of the polymer. The thickness of the adsorbed layers was characterized by XRR using synchrotron radiation at the European Synchrotron Radiation Facility (ESRF). The obtained results show that the polyelectrolyte adsorbs onto the surfactant monolayer as a thin film when favored by electrostatic interactions. Influence of polymer ionic charge, polymer concentration, and pH on the adsorption mechanism was also studied.