Surface energy modification and characterization of a plasma-polymerized fluoropolymer

This paper describes two methods of modifying the surface energy of a plasma-polymerized film. One method is to use diphenylamine (DPA) to stabilize the surface energy increase of the polymer caused on exposure to air or a polar liquid. Another method is to use heptafluorobutyric anhydride (HFBA) to reduce the surface energy of aged (oxidized) film. The HFBA-treated film displays the same surface energy (20 mJ/m2) as the freshly prepared film. It is, however, much more stable than the as-polymerized film in propylene glycol. Other silylation and fluorinated esterification reagents were found to be much less effective. The changes in surface energy were caused by changes in the chemical structure. The chemical changes were analyzed by infrared (IR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). These changes were either caused by oxidation of the film in air, water, and propylene glycol or were induced by fluorination of the oxidized film. The polymer used in this study is a copolymer of perfluoropropane (PFP) and 3,3,3-trifluoropropylmethyldimethoxysilane (TFPS). Other physical properties, such as solubility, thickness, coefficient of friction, adhesion, and thermal transitions of the polymer, have also been studied.