Polyelectrolyte multilayers: Simulations, experiments, and applications in biomineralization

Polyelectrolyte multilayer formation is achieved by alternate adsorption of oppositely charged polymers in a layer-by-layer (LbL) fashion from dilute polyelectrolyte solutions. This dissertation examines the formation, growth, structure, and morphology of polyelectrolyte multilayers by utilizing molecular dynamics (MD) simulations and polyelectrolyte spin assembly (PSA) experiments employing a spin-coating radial flow. Application of multilayers as substrates for biomineralization of hydroxyapatite (HA) and silica is also examined. MD simulations of assembly of flexible polyelectrolytes into multilayers were performed at a charged planar surface from dilute polyelectrolyte solutions. These simulations show that multilayer growth proceeds through surface overcharging, chain intermixing, and a linear increase in polymer surface coverage at each deposition step. The strong electrostatic attraction between oppositely charged polyelectrolytes at each deposition step is a driving force behind the multilayer growth. Polymer surface coverage and multilayer structure are each strongly influenced by the charge fraction of polyelectrolytes, as well as the strength of electrostatic and short-range interactions.; Experimental results from PSA elucidated the synergistic effect of the spin-speed and the solution ionic strength on the growth and morphology of multilayers. The growth rate and polymer surface coverage of multilayers shows a non-monotonic dependence on solution ionic strength, first increasing and then decreasing as the solution ionic strength is increased. This is a manifestation of two competing mechanisms responsible for multilayer formation in agreement with Flory-like theory of multilayer formation from polyelectrolyte solutions under flow. At low salt concentrations, the electrostatic interactions control the multilayer assembly process while, at high salt concentrations, the multilayer assembly it is dominated by shear flow.; For applications of multilayers in biomineralization, the possibility of forming HA and silica from simple synthetic macromolecules and polypeptides that have similar functionality as proteins found in nature was examined. Poly(glutamic acid) was studied for HA formation, while poly(lysine) and poly(ethylene imine) (PEI) were studied for silica formation. Such mineral formation was investigated on the surfaces of multilayers, in solutions, and on the polymer scaffolds formed using electrospinning or freeze-drying techniques.