A dynamic laser light-scattering study of chitosan in aqueous solution

The solution behavior of four chitosans (91% deacetylated chitin) with different molecular weights in 0.2M CH₃COOH/0.1M CH₃COONa aqueous solution was investigated at 25°C by dynamic laser light scattering (LLS). The Laplace inversion of the precisely measured intensity-intensity lime correlation function leads us to an estimate of the line-width distribution G(Γ), which could be further reduced too translational diffusion coefficient distributions G(D). By using a combination of static and dynamic LLS results, i.e., M_w and G (D), we were able to establish a calibration of D = k_DM with k_D = (3.14 ± 0.20) × 10⁻⁴ and α_D = 0.655 ± 0.015. By using this calibration, we successfully converted G(D) into a molecular weight distribution f_w(M). The larger α_D value confirms that the chitosan chain is slightly extended in aqueous solution even in the presence of salts. This is mainly due to its backbone and polyelectrolytes nature. As a very sensitive technique, our dynamic LLS results also revealed that even in dilute solution chitosan still forms a small amount of larger sized aggregates that have been overlooked in previous studies. The calibration obtained in this study will provide another way to characterize the molecular weight distribution of chitosan in aqueous solution at room temperature. © 1995 John Wiley & Sons, Inc.