Layer-by-Layer Assembled Films Composed of “Charge Matched” and “Length Matched” Polysaccharides: Self-Patterning and Unexpected Effects of the Degree of Polymerization

The functionalization of chitosan with carboxymethyl groups allows zwitterionic or anionic chitosan derivatives to be obtained as a function of the degree of substitution. Here, we show that polyelectrolyte multilayers of chitosan and carboxymethylchitosan can be assembled by “dipping” or “spraying” to form strongly hydrated films in which both the polyanion and polycation possess the same polymer backbone (“matched chemistries”). Such films grow rapidly to fairly large thickness in very few assembly steps, especially in the case of “matched” charge densities, and atomic force microscopy reveals the formation of surface patterns that are dependent on the deposition conditions and on the number of layers. Interestingly, the influence of the molar masses of the polyelectrolyte pairs on the complex formation is somewhat counterintuitive, the stronger complexation occurring between polyanions and polycations of different (“non-matching”) lengths.