The aqueous liquid/liquid interphases formed by chitosan-anionic surfactant complexes

Abstract

The solubility behavior of cationic chitosan complexes with two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl)sulfosuccinate (AOT), as well as the formation of gel-like membranes capable of separating two aqueous polymer and surfactant solutions has been investigated. The chitosan—surfactant complexes can exist either as homogenous clear solutions or precipitates or as membranes, depending on the molar ratio between the polymer structural units and the surfactant and the degree of protonation of the polymer. The transitions between the phases were determined and correlated with structural and compositional parameters. The conditions for the formation of new stable chitosan AOT microcapsules were observed and were compared with those of chitosan-SDS. The two surfactants with different structures behave very differently. SDS forms gel-like membrane with chitosan at a much lower concentrations than AOT, even though the former has a higher critical micellar concentration. It was postulated that in forming a gellike membrane from chitosan—surfactant complexes a certain role is played by the existence of micelles and their size and shape. The smaller, spherical, more abundant micelles in SDS solutions lead to the formation of mechanically resistant membranes at a lower concentration than AOT. The difference in behavior is more evident in the concentration domain where AOT forms lamellar self-assemblies. The added ethyl alcohol affects both the solubility curves and the membrane formation.