Development of Polyelectrolyte Complex Thin Films for Polymer Surface Functionalization

Abstract

Polyelectrolyte complexes (PEC) are composites of two or more polyelectrolytes, that when processed appropriately, can create thin films. These films can have a wide array of properties and can serve to functionalize a wide variety of surfaces. This dissertation discusses the functionalization of polymeric surfaces with polyelectrolyte complexes. The layer-by-layer assembly method was used to sequentially build up the PEC on the substrate. This process generally requires several steps to manufacture a film of sufficient thickness and/or surface coverage. In an effort to reduce the number of processing steps to form PEC thin films, development of a single step deposition method was also developed. Halloysite-based multilayer composites were found to significantly reduce the flammability of polyurethane foam. There was a 60% reduction in the peak heat release rate and total smoke release, and coated foam self-extinguished in open flame testing. This coating worked by forming a physical barrier that reduces heat and mass transfer during combustion, eventually leading to the flame extinguishing. Because of the environmentally-benign nature of the ingredients used, this coating provides a safe alternative to traditional flame retardant materials. Polyelectrolyte complex multilayers were applied to polyester fabric and bacterial adhesion was significantly reduced after a simple water rinse. >99% of deposited bacteria was removed after rinsing. Bioluminescent Staphylococcus aureus was used to evaluate viable bacteria on the fabric surface. Electrostatic repulsion iii between the negatively charged surface and the negatively charged bacteria combined with increasing surface roughness is believed to be the reason for reduced bacterial adhesion. Polyelectrolyte complexes were deposited to polyester fabric and film in a single step. Film structure and morphology are dependent on how the film is cured (i.e. formation of electrostatic network). Rough aggregated films were found to form when the coating is cured while it is still wet on the substrate surface, and is ideal for coating complex substrates (e.g. fabric). This coating was found to reduce bacterial adhesion and >95% of deposited bacteria is removed after a simple rinse with water. When the PEC coatings are cured after the film is dried to the surface of the substrate, a conformal relatively smooth coating is formed, and when applied to PET film, reduces oxygen transmission by two orders of magnitude. The transparency of this coating was found to be dependent on the concentration and ionic strength of the buffer in which the films are cured. These processes significantly reduce processing steps required to deposit films with similar properties using layer-by-layer.