This paper presents the results of our study of the diffusion front progression of OH − ions in the bulk of a flat layer of the salt chitosan form during the course of the chemical reaction of the polymer-analogous salt → base transformation, accompanied by the formation of a water-insoluble polymeric phase as a gel film with its structure of concentric rings or tangential bands. Using scanning electron microscopy and polarization microscopy, structural and morphological features of these periodic formations were visualized. Physicochemical parameters and spatiotemporal mass transfer characteristics were obtained. The process under study is shown to obey the classical laws of ion-exchange reactions, and the formation kinetics and the ratio of the positions of periodic structures are described by the laws characteristic of the Liesegang phenomenon. The average diffusion coefficients of hydroxide ions in the periodic formations calculated, considering the protonation degree of amino groups, were found to be no more than a decimal order of magnitude lower than those in an aqueous solution. This confirms the fact of swelling of the formed chitosan base and the existence of a gel film, in whose liquid phase diffusion occurs.

Structural and morphological features of chitosan gel films with a radially periodic structure, obtained by neutralizing the salt form of the polymer with sodium hydroxide or triethanolamine, were visualized by scanning electron microscopy. The formation of such supramolecularly ordered layered structures was found to obey diffusion kinetics and the regularities of Liesegang periodic precipitation. The revealed dependence of the morphostructure of our chitosan gel films on the neutralizing reagent used is due to differences in the diffusion rate of inorganic and organic substance, as well as some spatio-temporal features of the mass transfer process.