Characterization of Clusters and Unimers in Associating Solutions of Chitosan by Dynamic and Static Light Scattering

Association of two chitosans of different degrees of acetylation (DA) is studied in dilute water/acid/salt solutions by combined analysis of static and dynamic light scattering. The influence of sodium salt anions Cl-and CH3COO-on conformation of macromolecules and properties of clusters was studied. At DA = 15 mol%, the macromolecules exist either in rigid-rod (R-g/R-h = 2.7) or in coil (R-g/R-h = 1.8) conformations in the solvents containing NaCl and CH 3 COONa, respectively. Chitosans with higher DA = 28% dissolved in the solvent containing CH 3 COONa are in the collapsed state (R-g/R-h < 0.8), predicted by Dobrynin (Macromolecules, 2004). The clusters are of spherical form (0.8 < R-g/R-h < 1.2). CH3COONa promotes higher fractal dimensionality of clusters (2.2-2.4) than NaCl (1.9). Higher critical aggregation concentration is observed in NaCl. The other hydrodynamic methods (capillary viscometry, velocity sedimentation, and Tsvetkov diffusometry) do not detect the clusters, probably, because of their disruption during flow.