Chain Dynamics and Layering within Polyelectrolyte Multilayer Films

The current study is focused on understanding main factors affecting dynamics of polymer chains included within layer-by-layer (LbL) films and impact of chain dynamics on film structure. LbL films, or polyelectrolyte multilayers (PEMs), can be deposited on a variety of substrates such as silicon, glass, plastics, and metals via alternating adsorption of oppositely charged polymers. Modification of surfaces with LbL films impart the substrates with new properties and functionalities, such as controlled wettability and uptake of water or capability to retain and/or controllably release small molecules. For many applications of PEMs, specifically for constructing multifunctional films for sequential, multi-step delivery of bioactive compounds, it is critically important to understand and control film structure. There are two possible modes of the PEM growth: linear growth, with a small, constant increase in the film thickness at each dipping step (lPEMs), and non-linear growth, with per-cycle film mass increasing with the number of deposited layers (nlPEMs). PEMs can switch between linear and non-linear film growth as a function of pH, temperature, or number of deposited layers. My goal was to relate polyelectrolyte chain mobility to the mechanism of PEM film growth and to establish the origin of transitions between linear and non-linear growth regimes. This goal was accomplished in experiments which allowed direct observation of chain displacements and PEM structural evolution upon exposure of these films to solutions at varied pH and ionic strength. My findings widen the fundamental knowledge about the mechanism of LbL growth and can be used for developing theories and modeling of PEM films. Moreover, these results can be useful in designing polyelectrolyte nanoassemblies for \nbiomedical applications, such as drug delivery coatings for medical implants or tissue engineering matrices.