Surface reconstruction by a "grafting through" approach: polyacrylamide grafted onto chitosan film

Grafted polymers and polymer brushes in particular have attracted significant attention in the last 2 decades as a way to alter and control interfacial properties. In the case of polymer brushes on solid substrates, a high grafting density of polymer chains results in stretching of the polymer coils normal to the substrate surface due to the effect of excluded volume. In this study, polyacrylamide is grafted to the surface of relatively soft thin films of chitosan. The "grafting through" approach is used by introducing double C═C bonds to amino groups of chitosan. The acquired kinetic data of grafting along with AFM and ellipsometry characterization suggest that the chitosan substrate undergoes surface reconstruction during the grafting of PAAm and simultaneously induces PAAm growth inside the soft substrate. As a result, much higher amounts of grafted polymer are achieved in comparison to traditional hard substrates like silicon or glass. Additionally, selective plasma etching of PAAm reveals filament-like structures oriented normal to the surface.