Surface modification of porous polymeric materials using low-temperature plasmas

The results presented in this dissertation establish the low-temperature plasma treatment developed in our laboratory as a permanent surface modification for polymeric membranes. H₂O plasma treatment renders commercial polysulfone, polyethersulfone, and polyethylene membranes hydrophilic, demonstrating that this treatment is general to variety of membrane materials. Furthermore, H₂O plasma treatment modifies the entire cross section of highly asymmetric membranes. We attribute the extensive membrane modification to the high porosity of these materials and the unique design of our membrane holder, which allows maximal penetration of the plasma through the membrane. In the broadest sense, this work has potential applications for membranes used in the biotechnology, pharmaceutical, and food and beverage industries as well as waste water treatment.; The unifying hypothesis of this work was that plasma surface modification would best be understood, and ultimately controlled, through independent study of all aspects of the plasma system. The results of this dissertation demonstrate that our multi-faceted approach affords better process control by considering the molecular-level chemistry as well as achieving the desired membrane modification. OH radicals in the H₂O plasma system were determined to be the primary reactive species involved in hydrophilic membrane modification. The role of OH radicals in the H₂O plasma surface modification system was directly determined with our non-intrusive radical-imaging experiments. Surface loss of OH radicals was observed under all experimental conditions. A moderate reactivity of ∼50% was measured for OH radicals with the membranes employed in this study, confirming H₂O plasma treatment is general to a variety of polymeric membranes. OH radicals produced in H₂O plasmas modify these materials by producing covalently-bound C=O, C-O, O-H, O-C=O, and sulfate groups at the surface, as evidenced by XPS analysis. These results support the concurrent oxidation pathways we predicted based on organic structural theory.