Characterization of association phenomena in aqueous systems of chitosan of different hydrophobicity

Rheological, dynamical and structural properties of aqueous systems of chitosan (UM-chitosan) and hydrophobically-modified chitosans (HM-chitosan) are briefly reviewed. The effects of pH, level of surfactant addition, polymer concentration, and temperature on the rheological behavior, both in the linear and non-linear viscoelastic regime, have been scrutinized. These variables have the strongest impact on the rheological properties of the hydrophobically-modified chitosans. We observe the formation of concentration-induced gels for systems of UM-chitosan and HM-chitosans. Incipient gels are evolved at lower concentrations as the hydrophobicity of the polymer increases. Non-linear shear thinning behavior is found in semidilute solutions of UM-chitosan and HM-chitosan at higher shear rates. The magnitude of this effect depends on factors, such as pH, amount of surfactant, polymer concentration, and hydrophobicity of the polymer. The dynamic light scattering results from semidilute solutions of UM-chitosan and HM-chitosan show that the intermolecular association phenomena in the polymer solutions are promoted by decreasing temperature and increasing polymer concentration and hydrophobicity. The intensity light scattering measurements on semidilute solutions of UM-chitosan and HM-chitosans suggest that the systems have a fractal structure and the fractal dimension is approx. 2.