Polyelectrolyte layer interpenetration and swelling of alginate–chitosan multilayers studied by dual wavelength reflection interference contrast microscopy

Polyelectrolyte multilayers of alginate and either poly-l-lysine or chitosan have been studied with dual wavelength reflection interference contrast microscopy (DW-RICM). Alginates with different ratios of the two monomer residues, β-d-mannuronic acid (M) and α-l-guluronic acid (G) were included to study possible effects of specific divalent ions selected from their ability to influence gelation of alginate. Measurements of multilayer thickness revealed the importance of the preparation conditions. The multilayer thickness was reduced with increasing ionic strength following preparation, suggesting a dominance of an ordinary screening of the alginate component. The results indicate that the interaction between alginate and chitosan are different from that between alginate and poly-l-lysine, with the latter appearing to be more of a “hit-and-stick” reaction while rearrangements during the adsorption process is occurring to a larger extent in the preparation of the chitosan–alginate multilayers.