Intermolecular interactions and morphology of aqueous polymer/surfactant mixtures containing cationic chitosan and nonionic sorbitan esters

Abstract

In this study, the impact of surfactant molecular composition (saturated sorbitan monolaurate or unsaturated sorbitan monooleate) on polymer/surfactant assemblies was examined. Specifically, the associations between the cationic chitosan and the uncharged surfactants were monitored by surface tension, turbidity, and conductivity measurements. Bright field, confocal laser scanning, and transmission electron microscopy revealed that nanometer-sized chitosan/surfactant aggregates comprised of a chitosan-rich shell and a chitosan-poor core agglomerate at high surfactant concentrations to yield micrometer-scaled supramolecular structures with highly ordered internal structure. The size and architecture of these chitosan/surfactant assemblies were dependent on the structure and concentration of the surfactant employed. The association mechanism among chitosan, surfactant, and the chitosan/surfactant aggregates was discussed in terms of the semirigid polyelectrolyte character of chitosan and the hydrophobic character of sorbitan esters. This study provides important insight into the structural and physical parameters of surfactant that govern the formation of multicompartment polymer/surfactant assemblies.