Investigation of the Internal Chemical Composition of Chitosan-Based LbL Films by Depth-Profiling X‑ray Photoelectron Spectroscopy (XPS) Analysis

Chitosan-based thin films were assembled using the layer-by-layer technique, and the axial composition was accessed using X-ray photoelectron spectroscopy with depth profiling. Chitosan (CHI) samples possessing different degrees of acetylation (DA̅) and molecular weight (Mv̅) produced via the ultrasound-assisted deacetylation reaction were used in this study along with two different polyanions, namely, sodium poly­styrene­sulfonate (PSS) and carboxy­methyl­cellulose (CMC). When chitosan, a positively charged polymer in aqueous acid medium, was combined with a strong polyanion (PSS), the total positive charge of chitosan, directly related to its DA̅, was the key factor affecting the film formation. However, for CMC/CHI films, the pH of the medium and Mv̅ of chitosan strongly affected the film structure and composition. Consequently, the structure and the axial composition of chitosan-based films can be finely adjusted by choosing the polyanion and defining the chitosan to be used according to its DA and Mv̅ for the desired application, as demonstrated by the antibacterial tests