Defining the surface chemistry of ammonia-modified poly(tetrafluoroethylene-co-hexafluoropropylene) films

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film samples were su rface-modified by exposure to a UV-activated mercury/ammonia environment (c alled the "mercat reaction"), yielding a hydrophilic surface with a diversi ty of functional groups. We describe herein the functionality of mercat-mod ified FEP and ultimately hope to use these defined surfaces in biomedical a pplications, specifically to enhance the interaction of cells at the FEP in terface. Following the mercat reaction, advancing and receding water contac t angles decreased from 120 degrees/101 degrees for FEP to 71 degrees/27 de grees for mercat-modified FEP. By comparison to small molecule chemistry, w e had expected the film samples to have imine and nitrile functional groups ; however, XPS analysis of mercat-modified film samples indicated the prese nce of both nitrogen and oxygen functional groups. From a series of labelin g reactions, the surface functional groups were found to include nitrile, a mine, carboxylic acid, hydroxyl, and carbon-carbon double bonds. Hydrolysis of nitrile functional groups resulted in an increased carboxylic acid conc entration from 10% to 38% and decreased water contact angles from 71 degree s/27 degrees to 61 degrees/30 degrees. Bromination/amination of carbon-carb on double bonds resulted in an increased amine concentration from 8% to 10% and decreased water contact angles from 71 degrees/27 degrees to 54 degree s/24 degrees. Future studies will correlate surface chemistry of these defi ned mercat-modified FEP film samples with neuronal cellular response.