Influence of Polymerization Conditions and Postdeposition Oxidation on Polydopamine Film Characteristics

Polydopamine (PDA) is widely used as a universal surface modification layer due to its strong adhesion and chemical versatility. However, the properties of PDA films can vary significantly depending on polymerization conditions and postdeposition handling. In this study, we hypothesize that oxygen availability during deposition and subsequent exposure to air after film formation critically influence the physical structure and chemical reactivity of PDA coatings. PDA films were prepared under controlled variations in deposition time, substrate orientation, and stirring and characterized using contact angle measurements and atomic force microscopy (AFM). We show that stirring enhances oxygen transport, resulting in rougher PDA films, while horizontally placed, nonagitated samples yield smoother coatings. After deposition, water contact angles increased over time, consistent with surface oxidation. ATR-IR spectroscopy and electrochemical measurements confirmed that postdeposition oxidation leads to a loss of redox activity and reduced reactivity toward amine-containing polymers. These findings underscore the importance of both polymerization conditions and postdeposition handling in determining PDA film properties and demonstrate that the time elapsed after film formation is a critical factor for achieving reproducible surface functionalization.