Physical characterization of erodible multilayered polyelectrolyte thin films fabricated from plasmid DNA and synthetic polyamines

This thesis focuses on the physical characterization of morphological transformations that occur in erodible multilayered polyelectrolyte films fabricated by the layer-by-layer deposition of plasmid DNA and synthetic polyamines, using atomic force microscopy (AFM), scanning electron microscopy (SEM), and laser scanning confocal microscopy (LSCM). When incubated in aqueous media, these ultrathin (∼100 nm thick) films gradually erode and release DNA over periods of approximately 48 hours. Characterization by AFM and SEM revealed that these films transform from an initially smooth morphology to one that is characterized by interconnected ridges and valleys. Further incubation results in the decomposition of these features into nanoparticulate structures. The patterns and structures generated by this transformation are similar to those observed for the spinodal dewetting of thin films of conventional polymers. This behavior has not, however, been observed for this class of multilayered assemblies, for which long-range electrostatic interactions play significant roles in governing film structure and stability. The results of additional experiments demonstrate that it is possible to promote this behavior, prevent it, or control it by varying polymer structure, film composition, or the conditions to which these materials are exposed. The results of experiments using LSCM and AFM to characterize films fabricated using fluorescently labeled polyelectrolytes suggest a physical picture of the nanoparticulate morphology in which polyelectrolyte layers from the topmost portion of the film remain relatively undisturbed and are juxtaposed over an array of particulate structures formed by polyelectrolyte chains from the bottommost layers of the film. Investigations of the influence of film thickness on the characteristic length scales associated with this transformation revealed a complex relationship that did not follow trends derived from models developed to describe the spinodal dewetting of thin films of conventional materials. The results presented in this thesis suggest the basis of methods that could prove useful for the generation of nanostructure on complex surfaces and contribute to methods for the localized delivery of DNA from surfaces.