VISCOSITY OF DILUTE AQUEOUS-SOLUTIONS OF HYDROPHOBICALLY-MODIFIED CHITOSAN AND ITS UNMODIFIED ANALOG AT DIFFERENT CONDITIONS OF SALT AND SURFACTANT CONCENTRATIONS

Viscosity measurements have been carried out on dilute acid aqueous so lutions of chitosan and of hydrophobically modified chitosan (HM-chito san) with three different degrees of C12-aldehyde substitution. The ex periments were performed in the presence of different amounts of the c ationic surfactant cetyltrimethylammonium bromide (CTAB) (0-30 mm) and with and without salt addition. By using Huggins equation, the intrin sic viscosity [eta], and Huggins constant (k') were evaluated at diffe rent conditions. The intrinsic viscosity was shown to decrease with in creasing salt concentration. Addition of CTAB to polymer solutions wit hout NaCl causes the values of the intrinsic viscosity to decline and the values of k' to rise. These observations are reminiscent of those reported fi om solutions of chitosan and HM-chitosans without surfacta nt but with increasing salinity. It was observed that [eta] and k' dep endency on the CTAB concentration is also influenced by the degree of hydrophobic substitution, In the presence of 10 mM NaCl, both [eta] an d k' seem to be independent of surfactant concentration for both the u nmodified chitosan and the HM-chitosan. The features can be rationaliz ed in terms of screening of electrostatic repulsion.